Chapter 1 CROP PRODUCTION AND MANAGEMENT

1. Select the correct word from the following list and fill in the blanks. float, water, crop, nutrients, preparation

Answer:

(a) The same kind of plants grown and cultivated on a large scale at a place is called crop. 

(b) The first step before growing crops is preparation of the soil.

(c) Damaged seeds would float on top of water.

(d) For growing a crop, sufficient sunlight and nutrients and water from the soil are essential.

2. Match items in column A with those in column B.

column A….. column B

Answer:

(i) Kharif crops….. (e) Paddy and maize

(ii) Rabi crops….. (d) Wheat, gram, pea

(iii) Chemical fertilisers….. (b) Urea and super phosphate

(iv) Organic manure….. (c) Animal excreta, cow dung, urine and plant waste

3. Give two examples of each.

Answer:

(a) Kharif crop:
(a) Examples of Kharif crop are paddy, maize, soyabean, cotton, etc.  

(b) Rabi crop:
(b) Examples of Rabi crop are wheat, gram, pea, mustard, etc. 

4. Write a paragraph in your own words on each of the following.

(a) Preparation of soil  

(b) Sowing  

(c) Weeding

(d) Threshing

Answer:

(a) Preparation of soil: Soil preparation involves loosening and turning over the soil to facilitate root growth, water retention, and nutrient uptake. The soil is tilled to break up large clumps and to mix in organic matter like compost or manure. The process also involves leveling the soil to create a uniform surface for planting.  

(b) Sowing: Sowing refers to the process of planting seeds in the soil. This can be done manually or using machines like seed drills. The seeds are placed at the correct depth and spacing to ensure that they get the required nutrients and water to grow properly.  

(c) Weeding: Weeding is the process of removing unwanted plants or weeds from the field. Weeds compete with crops for resources like water, nutrients, and sunlight. They can be removed by hand or using tools like a hoe or a weed cutter.

(d) Threshing: Threshing is the process of separating grains from the harvested crop. This can be done manually by beating the crop with a stick or using a machine like a thresher. 

5. Explain how fertilisers are different from manure.

Answer:

Fertilizers are chemical compounds that are added to the soil to enhance the nutrient content, promote plant growth and increase yield. They are available in the form of solid or liquid and contain a specific ratio of essential nutrients. On the other hand, manure is organic matter like animal waste or decomposed plant material, which is added to the soil to improve its fertility. Manure releases nutrients slowly over time and also helps to improve soil structure, water-holding capacity, and aeration.

6. What is irrigation? Describe two methods of irrigation which conserve water.

Answer:

Irrigation refers to the process of providing water to crops artificially when there is not enough rainfall. Two methods of irrigation that conserve water are drip irrigation and sprinkler irrigation. In drip irrigation, water is delivered directly to the roots of the plants using a network of pipes and emitters. This method reduces water loss due to evaporation and seepage. In sprinkler irrigation, water is sprayed over the crop using sprinklers. This method uses less water than flood irrigation as it reduces water loss due to evaporation.

7. If wheat is sown in the kharif season, what would happen? Discuss.

Answer:

Wheat is a Rabi crop and requires a cool climate for its growth. If wheat is sown in the Kharif season, it will not get the required climate and sunlight for proper growth. The crop may suffer from diseases, pests, and poor growth due to high temperature and rainfall. The yield will be low, and the quality of the grains will also be poor.

8. Explain how soil gets affected by the continuous plantation of crops in a field.

Answer:

Continuous plantation of crops in a field leads to soil exhaustion and depletion of nutrients. The repeated cultivation of the same crop in a field decreases the level of essential nutrients, which affects the growth of crops. The soil becomes compacted, loses its structure, and reduces water-holding capacity. Continuous cropping also leads to an increase in pests and diseases, as the same organisms survive in the soil and infect the next crop.

9. What are weeds? How can we control them?

Answer:

Weeds are unwanted plants that grow along with crops and compete for nutrients, water, and sunlight. They can affect the growth and yield of crops. Weeds can be controlled by using cultural, physical, and chemical methods. Cultural methods include crop rotation, intercropping, and mulching. Physical methods involve removing weeds by hand or using tools like a hoe or a weed cutter. Chemical methods involve the use of herbicides, which kill or control the growth of weeds. However, care must be taken while using herbicides, as they can also harm crops and the environment if not used properly.

10. Arrange the following boxes in proper order to make a flow chart of sugarcane crop production.

1.Sending crop to sugar factory

2.Irrigation  

3.Harvesting  

4.Sowing

5.Preparation of soil

6.Ploughing the field  

7.Manuring

Answer:

(a) Preparation of soil - 5

(b) Sowing - 4

(c) Irrigation - 7

(d) Manuring - 6

(e) Harvesting - 3

(f) Ploughing the field - 2

(g) Sending crop to sugar factory – 1

11. Complete the following word puzzle with the help of clues given below.

Down 1. Providing water to the crops. 2. Keeping crop grains for a long time under proper conditions. 5. Certain plants of the same kind grown on a large scale.  

Across 3. A machine used for cutting the matured crop. 4. A rabi crop that is also one of the pulses. 6. A process of separating the grain from chaff.

Answer:  

Down:

     Irrigation

     Storage

     Crop

Across:

3. Harvester

    Gram

    Threshing

Extended Learning — Activities and Projects 1.  

Sow some seeds in the soil and arrange to water them by drip irrigation. Observe daily.

Answer:

Sowing seeds in the soil and arranging for drip irrigation is a great way to conserve water. Drip irrigation delivers water directly to the roots of the plants, which reduces evaporation and water loss due to run off.  

By using drip irrigation, the plants can receive the right amount of water they need without wasting any. Observing daily will help you see how the plants respond to the drip irrigation and how much water is being used. It's a great experiment to learn more about the importance of water conservation in crop production.

(i) Do you think it can save water?  

(i) Yes, drip irrigation can save water as it delivers water directly to the roots of the plants, which reduces evaporation and water loss due to run off.

ii) Note the changes in the seed.

(ii)We notice that the seeds germinate faster and grow stronger with drip irrigation than with other irrigation methods.

2. Collect different types of seeds and put them in small bags. Label them.

Answer:

We collected different types of seeds and labelled them as below:

Bhindi Seed: Labelled them as Okra.

Tori Seed: Labelled them as Snake guard.

Kerala Seed: Labelled it as Bitter guard.

Mirchi Seed: Labelled it as Chilli.

3. Collect pictures of some other agricultural machines and paste them in a file. Write their names and uses.

Answer:

Collecting pictures of different agricultural machines and writing their names Some examples of machines include tractors, harvesters, and, Shovel.

4. Project Work Visit a farm, nursery or a garden nearby. Gather information about

Answer:

(i) importance of seed selection.

Seed selection is important because it affects the quality and yield of the crop.

(ii) method of irrigation

Irrigation methods affect water usage and crop growth.  

Important Questions

1. Fill in the blanks.

Answer:

(a) Microorganisms can be seen with the help of a __Microscope__.

(b) Blue green algae fix ____Nitrogen___ directly from air and enhance fertility of soil.  

(c) Alcohol is produced with the help of ___Yeast_____.

(d) Cholera is caused by ___Vibrio cholerae___.

2. Tick the correct answer.

Answer:

(a) Yeast is used in the production of 

(i) sugar

(ii) alcohol

(iii) hydrochloric acid

(iv) oxygen

Answer…..(ii) alcohol    

(b) The following is an antibiotic 

(i) Sodium bicarbonate

(ii) Streptomycin

(iii) Alcohol

(iv) Yeast

Answer…..(ii) Streptomycin

(c) Carrier of malaria-causing protozoan is 

(i) female Anopheles mosquito

(ii) cockroach

(iii) housefly

(iv) butterfly

Answer…..(i) female Anopheles mosquito  

(d) The most common carrier of communicable diseases is 

(i) ant

(ii) housefly

(iii) dragonfly

(iv) spider

Answer…..(ii) housefly

(e) The bread or idli dough rises because of 

(i) heat

(ii) grinding

(iii) growth of yeast cells

(iv) kneading

Answer…..(iii) growth of yeast cells  

(f) The process of conversion of sugar into alcohol is called 

(i) nitrogen fixation

(ii) moulding

(iii) fermentation

(iv) infection

Answer…..(iii) fermentation

3. Match the organisms in Column A with their action in Column B.

Answer:

Column A….. Column B  

(i) Bacteria….. (a) Fixing nitrogen

(ii) Rhizobium….. (b) Forming nodules on roots of leguminous plants

(iii) Lactobacillus….. (c) Fermenting milk to form curd

(iv) Yeast….. (d) Fermenting sugar to form alcohol

(v) Plasmodium….. (e) Causing malaria

(vi) Vibrio cholerae….. (f) Causing cholera

(vii) HIV virus….. (g) Causing AIDS

4. Can microorganisms be seen with the naked eye? If not, how can they be seen

Answer:

Microorganisms cannot be seen with the naked eye as they are very small. They can be seen using a microscope, such as a compound microscope or an electron microscope, which can magnify their image and make them visible to the human eye.

5. What are the major groups of microorganisms?

Answer:

The major groups of microorganisms are bacteria, viruses, fungi, protozoa, and algae.

6. Name the microorganisms which can fix atmospheric nitrogen in the soil.

Answer:

Rhizobium and blue-green algae (cyanobacteria) are the microorganisms that can fix atmospheric nitrogen in the soil.

7. Write 10 lines on the usefulness of microorganisms in our lives.

Answer:

Microorganisms have numerous benefits in our lives. They are used to produce a variety of products such as antibiotics, vaccines, and enzymes for industrial and medical purposes. They are also used in food production, including fermentation of bread, cheese, and yogurt. Microorganisms play a crucial role in decomposing dead matter and returning nutrients to the soil, which is important for agriculture. They also help to clean up environmental pollutants and to treat wastewater. In addition, microorganisms are used in research to understand biological processes and to develop new treatments for diseases.

8. Write a short paragraph on the harmful effects of microorganisms.

Answer:

Microorganisms can cause many harmful effects, including disease and infections in humans, animals, and plants. Bacteria, viruses, and fungi can cause a variety of illnesses such as pneumonia, tuberculosis, and meningitis. Some microorganisms can also produce toxins that can harm humans and animals. Microorganisms can also spoil food and cause damage to crops, leading to economic losses. In addition, some microorganisms can degrade materials such as wood, paper, and textiles, causing damage to buildings and other structures.

9. What are antibiotics? What precautions must be taken while taking antibiotics?

Answer: 

Antibiotics are medicines used to treat bacterial infections. They work by killing or slowing the growth of bacteria. Precautions that should be taken while taking antibiotics include taking the full course of antibiotics as prescribed, even if symptoms improve before the medication is finished. This helps to prevent antibiotic resistance. Patients should also avoid sharing antibiotics with others and only take antibiotics prescribed by a healthcare professional. In addition, some antibiotics can have side effects, so patients should talk to their doctor if they experience any adverse reactions.

Important Questions

1. Explain why some fibres are called synthetic.

Answer:

Synthetic fibres are made from chemicals or petrochemicals, unlike natural fibres that are obtained from plants or animals. Hence, they are called synthetic.

2. Mark (V) the correct answer.

Rayon is different from synthetic fibres because

(a) it has a silk-like appearance.  

(b) it is obtained from wood pulp. 

(c) its fibres can also be woven like those of natural fibres.

Answer..... Explanation:

(b) Rayon is obtained from wood pulp, which is a natural source, unlike synthetic fibres that are made from chemicals or petrochemicals.

3. Fill in the blanks with appropriate words.

(a) Synthetic fibres are also called ___artificial__ or ___man-made___ fibres.  

(b) Synthetic fibres are synthesised from raw material called __petrochemicals__ . 

(c) Like synthetic fibres, plastic is also a ___synthetic material___ .

4. Give examples which indicate that nylon fibres are very strong.

Answer:

Nylon fibres are used to make ropes, fishing nets, and parachutes because of their high strength.

5. Explain why plastic containers are favoured for storing food.

Answer:

Plastic containers are favoured for storing food because they are lightweight, unbreakable, and provide a barrier against moisture and air, which helps to keep food fresh for a longer time.

6. Explain the difference between thermoplastic and thermosetting plastics.

Answer:

Thermoplastic plastics can be easily melted and re-molded into new shapes, whereas thermosetting plastics cannot be melted once they are formed into a shape and become hard and rigid.

7. Explain why the following are made of thermosetting plastics.

(a) Saucepan handles

Answer:

Saucepan handles are made of thermosetting plastics because they can withstand heat and do not melt easily.  

(b) Electric plugs/switches/plug boards  

Electric plugs/switches/plug boards are made of thermosetting plastics because they are strong and can withstand high temperatures and electrical shocks. 

8. Categorise the materials of the following products into ‘can be recycled’ and ‘cannot be recycled’.

Telephone instruments, plastic toys, cooker handles, carry bags, ball point pens, plastic bowls, plastic covering on electrical wires, plastic chairs, electrical switches.

Answer:

Can be recycled:

Plastic toys

Carry bags

Ball point pens

Plastic bowls

Plastic covering on electrical wires

Plastic chairs

Cannot be recycled:

Telephone instruments

Cooker handles

Electrical switches

9. Rana wants to buy shirts for summer. Should he buy cotton shirts or shirts made from synthetic material? Advise Rana, giving your reason.

Answer:

Rana should buy cotton shirts for summer because cotton is a natural fibre that allows air to pass through, keeping the body cool and comfortable in hot weather.

10. Give examples to show that plastics are non corrosive in nature.

Answer:

Plastics do not react with most substances and are not affected by moisture, making them non-corrosive. For example, plastic pipes used for carrying water do not corrode or rust over time.

11. Should the handle and bristles of a tooth brush be made of the same material? Explain your answer.

Answer:

The handle and bristles of a toothbrush should not be made of the same material. The handle should be made of a rigid material, whereas the bristles should be soft and flexible for effective cleaning of teeth.

12. ‘Avoid plastics as far as possible’. Comment on this advice.

Answer:

Plastics are widely used in various industries because of their versatile properties, but they are not biodegradable and can take hundreds of years to decompose, causing harm to the environment. Hence, we should avoid using plastics as far as possible and switch to eco-friendly alternatives.

13. Match the terms of column A correctly with the phrases given in column B:

Column A..... Column B

(i) Polyester….. (d) Fabrics do not wrinkle easily

(ii) Teflon….. (c) Used to make non-stick cookwares

(iii) Rayon….. (a) Prepared by using wood pulp

(iv) Nylon….. (b) Used for making parachutes and stockings

14. ‘Manufacturing synthetic fibres is actually helping conservation of forests’. Comment.  

Answer:

‘Manufacturing synthetic fibres is actually helping conservation of forests’. Comment:

The statement is partially true. Manufacturing synthetic fibres does help conserve forests as it reduces the need for natural fibres that require land and water resources for cultivation, such as cotton and silk. However, synthetic fibres are derived from non-renewable resources like petroleum, and the production process also involves the use of various chemicals that can have negative impacts on the environment. Therefore, the statement should be viewed in the context of a trade-off between the conservation of forests and the potential negative impacts of synthetic fibre production.

15. Describe an activity to show that thermoplastic is a poor conductor of electricity.

Answer:

Thermoplastic is a poor conductor of electricity, we can show this with a simple activity:

Ist take a thermoplastic object such as a plastic spoon and connect it to a battery with wires.  

Then, touch the wires to a bulb. It will not light up because the plastic is a poor conductor of electricity. This is because thermoplastic materials have high resistance to the flow of electric current, which means they cannot conduct electricity efficiently.

Important Questions

1. Which of the following can be beaten into thin sheets?

(a) Zinc 

(b) Phosphorus 

(c) Sulphur 

(d) Oxygen  

Answer:

(a) Zinc can be beaten into thin sheets.

2. Which of the following statements is correct?

(a) All metals are ductile.  

(b) All non-metals are ductile.  

(c) Generally, metals are ductile.

(d) Some non-metals are ductile.

Answer:

(c) Generally, metals are ductile.

3. Fill in the blanks.

(a) Phosphorus is a very __reactive___ non-metal.

(b) Metals are __conductors ____of heat and ___electricity___.

(c) Iron is ___more___ reactive than copper.

(d) Metals react with acids to produce ___hydrogen___ gas.

4. Mark ‘T’ if the statement is true and ‘F’ if it is false.

(a) Generally, non-metals react with acids. ...... (F)

(b) Sodium is a very reactive metal...... (T)

(c) Copper displaces zinc from zinc sulphate solution...... (F)

(d) Coal can be drawn into wires...... (F)

5. Some properties are listed in the following Table. Distinguish between metals and non-metals on the basis of these properties.

Properties…..Metals…..Non-metals

1. Appearance…..Shiny…..Dull

2. Hardness…..Hard…..Soft

3. Malleability…..Malleable…..Non-malleable

4. Ductility…..Ductile…..Non-ductile

5. Heat Conduction…..Good conductor…..Poor conductor

6. Conduction of Electricity…..Good conductor…..Poor conductor

6. Give reasons for the following.

Answer:

(a) Aluminium foils are used to wrap food items:  

Aluminium is a malleable metal that can be easily rolled into thin sheets. It does not react with food items and hence is used to wrap food items.

(b) Immersion rods for heating liquids are made up of metallic substances:  

Metals are good conductors of heat and electricity. Hence, they are used to make immersion rods that can heat liquids quickly and efficiently.

(c) Copper cannot displace zinc from its salt solution:

Copper is less reactive than zinc and hence cannot displace it from its salt solution.

(d) Sodium and potassium are stored in kerosene:

Sodium and potassium are highly reactive metals that react vigorously with air and water. Hence, they are stored in kerosene to prevent their reaction with air and moisture.

7. Can you store lemon pickle in an aluminium utensil? Explain.

Answer:

No, lemon pickle cannot be stored in an aluminium utensil because acids present in the pickle can react with aluminium to produce harmful compounds. This can also spoil the taste and quality of the pickle.

8. Match the substances given in Column A with their uses given in Column B.

Column A…... Column B

(i) Gold ….. Jewellery

(ii) Iron ….. Machinery

(iii) Aluminium ….. Wrapping food

(iv) Carbon ….. Fuel

(v) Copper ….. Electric wire

(vi) Mercury ….. Thermometers

9. What happens when

(a) Dilute sulphuric acid is poured on a copper plate?  

Answer:

When dilute sulphuric acid is poured on a copper plate, the copper reacts with the acid to form copper sulfate and hydrogen gas is evolved.

Word equation: Copper + Dilute sulphuric acid → Copper sulfate + Hydrogen gas Chemical Chemical equation: Cu + H2SO4 → CuSO4 + H2  

(b) Iron nails are placed in copper sulphate solution? Write word equations of the reactions involved.

Answer:

When iron nails are placed in copper sulphate solution, iron displaces copper from copper sulfate solution and forms iron sulfate. The blue colour of copper sulfate solution fades and reddish-brown coating of copper is deposited on the iron nails.  

Word equation: Iron + Copper sulfate solution → Iron sulfate solution + Copper Chemical equation: Chemical Equation: Fe + CuSO4 → FeSO4 + Cu

10. Saloni took a piece of burning charcoal and collected the gas evolved in a test tube.

(a) How will she find the nature of the gas?  

Answer:

Saloni can perform the following tests to find the nature of the gas:

Place a burning splint near the mouth of the test tube. If the gas is oxygen, the burning splint will rekindle. If the gas is hydrogen, it will produce a popping sound.

If the gas is carbon dioxide, it will turn lime water milky when passed through it.

(b) Write down word equations of all the reactions taking place in this process.

Answer:

When a piece of burning charcoal is collected in a test tube, carbon dioxide and other gases are evolved.

Word equation: Charcoal + Oxygen → Carbon dioxide + Water + Other gases

Chemical equation: C + O2 → CO2 + H2O + Other gases

11. One day Reeta went to a jeweller’s shop with her mother. Her mother gave an old gold jewellery to the goldsmith to polish. Next day when they brought the jewellery back, they found that there was a slight loss in its weight. Can you suggest a reason for the loss in weight?

Answer:

The reason for the slight loss in weight of the gold jewellery after polishing is that the goldsmith removes the thin layer of gold from the surface of the jewellery during the polishing process. This results in a slight loss in weight 

Important Questions

Q. Explain why fossil fuels are exhaustible natural resources. 

1. What are the advantages of using CNG and LPG as fuels?  

Answer:

The advantages of using CNG and LPG as fuels are:

They are cleaner fuels and emit less harmful pollutants compared to petrol and diesel.

They are more efficient and economical fuels.

They can be easily transported and stored in compressed form.

2. Name the petroleum product used for surfacing of roads.  

Answer:

Bitumen is the petroleum product used for surfacing of roads.

3. Describe how coal is formed from dead vegetation. What is this process called?

Answer:  

Coal is formed from dead vegetation through a process called carbonisation. During this process, the dead vegetation gets buried under sediment and heat and pressure from the overlying layers gradually transform it into coal over millions of years.

4. Fill in the blanks.  

(a) Fossil fuels are __coal__, __petroleum___, and __natural gas__.

(b) Process of separation of different constituents from petroleum is called __refining__.

(c) Least polluting fuel for vehicle is__ C.N.G.__.

5. Tick True/False against the following statements.

(a) Fossil fuels can be made in the laboratory. (T/F)  

(a) False, fossil fuels cannot be made in the laboratory.

(b) C.N.G. is more polluting fuel than petrol. (T/F)  

(b) False, C.N.G. is a less polluting fuel compared to petrol.

(c) Coke is almost pure form of carbon. (T/F)

(c) True, coke is almost pure form of carbon.

(d) Coal tar is a mixture of various substances. (T/F)  

(d) True, coal tar is a mixture of various substances.

(e) Kerosene is not a fossil fuel. (T/F)  

(e) False, kerosene is a fossil fuel.

6. Explain why fossil fuels are exhaustible natural resources  

Answer:

Fossil fuels are exhaustible natural resources because they take millions of years to form under specific geological conditions and are being consumed at a much faster rate than they are being formed. It is estimated that the reserves of fossil fuels will deplete within a few decades, and there is a need for alternative and sustainable sources of energy.

7. Describe characteristics and uses of coke.  

Answer:

Characteristics and uses of Coke are as under:

Coke is a grey, hard, and porous substance that is made by heating coal in the absence of air. It is composed mainly of carbon and is a good fuel as it burns with a smokeless flame. Some of the characteristics and uses of coke are:

Characteristics:

Coke is a hard and porous substance.

It is composed mainly of carbon and has a high calorific value.

It burns with a smokeless flame.

It is a good reducing agent.

It is an excellent fuel for the production of iron and steel.

Uses:

Coke is used as a fuel in many industries, including iron and steel production, cement manufacturing, and electricity generation.

It is used as a reducing agent in the production of metals.

It is also used in the manufacture of chemicals, such as carbon black and calcium carbide.

8. Explain the process of formation of petroleum. 

Answer:

Process of Formation of Petroleum is as under:

Petroleum is a fossil fuel that is formed from the remains of dead marine organisms. The process of formation of petroleum can be explained as follows:

Dead marine organisms, such as plankton, algae, and bacteria, sink to the bottom of the ocean and are buried under sediment.

Over time, the sediment and organic matter are subjected to high pressure and temperature, which converts them into a waxy material called kerogen.

As the temperature and pressure increase further, the kerogen is transformed into liquid and gaseous hydrocarbons, which migrate upwards through porous rock formations until they are trapped by impermeable rocks or geological structures, forming reservoirs of petroleum.

The petroleum can then be extracted from the reservoirs using drilling techniques and refined into various products, such as gasoline, diesel, and jet fuel

9. The following Table shows the total power shortage in India from 1991–1997. Show the data in the form of a graph. Plot shortage percentage for the years on the Y-axis and the year on the X-axis. S. No…Year... Shortage (%)  

1 …...1991 ….. 7.9  

2 ….. 1992 ….. 7.8  

3  …..1993 ….. 8.3  

4 ….. 1994 ….. 7.4

5 ….. 1995 ….. 7.1

6 ….. 1996 ….. 9.2

7 ….. 1997 …...11.5  

Answer:

Sketch Graph.

Important Questions

1. List conditions under which combustion can take place.

Answer:

Conditions under which combustion can take place are presence of fuel, oxygen and heat.

2. Fill in the blanks.  

(a) Burning of wood and coal causes__pollution __of air.

(b) A liquid fuel, used in homes is __LPG__.

(c) Fuel must be heated to its __ignition temperature __before it starts burning.

(d) Fire produced by oil cannot be controlled by __water__.

3. Explain how the use of CNG in automobiles has reduced pollution in our cities.  

Answer:

The use of CNG in automobiles has reduced pollution in our cities as it produces less harmful gases like carbon monoxide, nitrogen oxides and particulate matter as compared to petrol or diesel.

4. Compare LPG and wood as fuels

Answer:

LPG is a better fuel than wood as it is more efficient, gives more energy.

LPG is a better fuel than wood as it is cleaner fuel, gives no smoke.

LPG is a better fuel than wood as it is easy to store, takes less space and does not get rotten.

LPG is a better fuel than wood as it is easier to transport.

5. Give reasons.

(a) Water is not used to control fires involving electrical equipment.  

Reason:

(a) Water is not used to control fires involving electrical equipment as it is a good conductor of electricity and can cause electrocution.

(b) LPG is a better domestic fuel than wood.  

Reason:

(b) LPG is a better domestic fuel than wood as it burns cleanly and efficiently, producing less smoke and soot.

(c) Paper by itself catches fire easily whereas a piece of paper wrapped around an aluminium pipe does not.

Reason:

(c) A piece of paper wrapped around an aluminium pipe does not catch fire easily because aluminium is a good conductor of heat and conducts heat away from the paper, preventing it from reaching its ignition temperature.

6. Make a labelled diagram of a candle flame.  

A labelled diagram of a candle flame:

Sketch

7. Name the unit in which the calorific value of a fuel is expressed.

Answer:

The unit in which the calorific value of a fuel is expressed is kilojoules per kilogram (kJ/kg).

8. Explain how CO2 is able to control fires.

Answer:

CO2 is able to control fires by displacing oxygen, which is necessary for combustion, from the  

surrounding area.

9. It is difficult to burn a heap of green leaves but dry leaves catch fire easily. Explain.

Answer:

Green leaves contain a lot of water and moisture, which makes it difficult to reach the ignition temperature required for combustion. Dry leaves, on the other hand, have less moisture and can easily reach the required ignition temperature.

10. Which zone of a flame does a goldsmith use for melting gold and silver and why?  

Answer:

A Goldsmith uses the outermost, Non luminous flame which is blue in colour for melting gold and silver. The reason is ,It is the hottest part of the flame and has the maximum heat energy.  

11. In an experiment 4.5 kg of a fuel was completely burnt. The heat produced

was measured to be 180,000 kJ. Calculate the calorific value of the fuel.

Answer:

Calorific value is =Amount of heat produced/Weight of fuel burnt

Substituting values in equation

Calorific value is = 180000 kJ / 4.5 Kg

Calorific value is = 180000 x 10/45

Calorific value is = 40000 Kj /kg

Answer: 40000 Kj /kg

12. Can the process of rusting be called combustion? Discuss.

Answer:

However both are chemical processes, but, we can not call rusting as combustion for the following reasons:

Rusting is a slow process and combustion is fast.

Rusting does not produce heat and light, but combustion does.

Rusting needs moisture to happen, but moisture is not required in combustion.

13. Abida and Ramesh were doing an experiment in which water was to be

heated in a beaker. Abida kept the beaker near the wick in the yellow part

of the candle flame. Ramesh kept the beaker in the outermost part of the

flame. Whose water will get heated in a shorter time?

Answer:

We know that, the outermost flame is the hottest one. Ramesh kept his beaker there.

Zone near the wick is not so hot. This is the middle zone and is of yellow colour. Abida kept her beaker there.

So, the Ramesh's beaker will get heated in a shorter time.

Important Questions

1. Fill in the blanks.

(a) A place where animals are protected in their natural habitat is called __wildlife sanctuary__.  

(b) Species found only in a particular area is known as ___endemic species__. 

(c) Migratory birds fly to far away places because __season __changes.

2. Differentiate between the following.

Answer:

(a) Wildlife sanctuary and biosphere reserve  

(a) Wildlife sanctuary is a protected area for the conservation of a particular species or group of species, while a biosphere reserve is a larger area of land that includes one or more protected areas, along with areas for sustainable use and human settlements.  

(b) Zoo and wildlife sanctuary  

(b) A zoo is a facility where animals are kept for public display and education, while a wildlife sanctuary is a protected area where animals are allowed to live in their natural habitat without human interference.

(c) Endangered and extinct species  

(c) Endangered species are those species that are at the risk of becoming extinct, while extinct species are those species that no longer exist on Earth.

(d) Flora and fauna  

(d) Flora refers to the plant species found in a particular region, while fauna refers to the animal species found in a particular region.

3. Discuss the effects of deforestation on the following.

Answer:

(a) Wild animals:  

(a) Deforestation can lead to loss of habitat and food sources for wild animals, which can cause a decline in their population.  

(b) Environment:  

(b) Deforestation can contribute to climate change, soil erosion, and loss of biodiversity, which can have long-term effects on the environment.  

(c) Villages (Rural areas):

(c) Villages located near deforested areas may face reduced water availability, soil degradation, and decreased crop yields.

(d) Cities (Urban areas):  

(d) Cities located near deforested areas may experience increased air pollution, reduced rainfall, and increased risk of natural disasters.

(e) Earth:  

(e) Deforestation can contribute to soil erosion, loss of biodiversity, and climate change, which can have negative impacts on the earth's ecosystems.  

(f) The next generation:

(f) Deforestation can have long-term effects on the next generation by reducing biodiversity and contributing to climate change.

4. What will happen if.

(a) we go on cutting trees.  

(a) If we go on cutting trees, it can lead to deforestation, loss of biodiversity, and climate change.  

(b) the habitat of an animal is disturbed.  

(b) If the habitat of an animal is disturbed, it can lead to a decline in its population and even extinction.  

(c) the top layer of soil is exposed.  

(c) If the top layer of soil is exposed, it can lead to soil erosion, loss of nutrients, and decreased soil fertility.

5. Answer in brief.

Answer:

(a) Why should we conserve biodiversity?  

(a) Biodiversity conservation is important for maintaining ecological balance, sustaining human life, and preserving cultural and economic values.  

(b) Protected forests are also not completely safe for wild animals. Why?   

(b) Protected forests may still face threats from human activities such as poaching, logging, and encroachment.  

(c) Some tribals depend on the jungle. How?

(c) Some tribals depend on the jungle for their livelihood, as they rely on forest products for food, shelter, and medicine.

(d) What are the causes and consequences of deforestation?

(d) Deforestation is caused by human activities such as logging, agriculture, and urbanization, and it can lead to loss of biodiversity, climate change, and soil erosion.

(e) What is Red Data Book?  

(e) Red Data Book is a document that lists and categorizes endangered and threatened species in a particular region.  

(f) What do you understand by the term migration?

(f) Migration refers to the seasonal movement of animals from one place to another in search of food, breeding opportunities, and favorable conditions.

6. In order to meet the ever-increasing demand in factories and for shelter, trees are being continually cut. Is it justified to cut trees for such projects? Discuss and prepare a brief report.  

Answer:

Cutting trees for industrial and urban development should be done with caution, as it can have negative impacts on the environment and local communities. Alternatives such as sustainable forestry, recycling, and using alternative materials should be explored. Efforts should also be made to promote reforestation and afforestation to compensate for the loss of trees.

7. How can you contribute to the maintenance of green wealth of your locality? Make a list of actions to be taken by you. 

Answer:

Actions that can contribute to the maintenance of green wealth of a locality include planting trees, reducing waste and pollution, conserving water, promoting sustainable practices, and supporting local conservation efforts.

8. Explain how deforestation leads to reduced rainfall. 

Answer:

Deforestation can lead to reduced rainfall because trees play an important role in the water cycle. Trees absorb water from the ground and release it into the atmosphere through a process called transpiration. This process contributes to the formation of clouds and ultimately leads to precipitation, including rainfall. When trees are cut down, the amount of water that is released into the atmosphere is reduced, which can lead to less rainfall in the area. Deforestation can also lead to soil erosion, which can further reduce the amount of water available for plant growth and precipitation.

9. Find out about national parks in your state. Identify and show their location on the outline map of India.

Answer:

The national parks in each state of India can vary. You can find information on the national parks in your state by visiting the website of the National Parks and Wildlife Sanctuaries of India. Once you have identified the national parks in your state, you can locate them on an outline map of India by using a map or atlas.

10. Why should paper be saved? Prepare a list of ways by which you can save paper

Answer:

Paper should be saved because it is made from trees, which are a valuable natural resource. Cutting down trees to make paper contributes to deforestation and the loss of important habitats for wildlife. Additionally, paper production consumes a significant amount of energy and contributes to greenhouse gas emissions.  

Here are some ways to save paper:

Use both sides of the paper when printing or writing.

Avoid printing unnecessary documents.

Use digital documents and emails instead of paper whenever possible.

Use reusable bags instead of paper bags.

Opt for electronic bills and statements instead of paper ones.

Use cloth napkins instead of paper napkins.

Buy recycled paper products.

11. Complete the word puzzle.

Down  

1. Species on the verge of extinction.

2. A book carrying information about endangered species.

5. Consequence of deforestation.  

Across  

1. Species which have vanished.

3. Species found only in a particular habitat.

4. Variety of plants, animals and microorganisms found in an area  

Answer:

Down

Endangered

Red Data Book

Soil erosion

Across

Extinct

Endemic

Biodiversity

Important Questions

1. Indicate whether the following statements are True (T) or False (F).

Answer:

(a) Unicellular organisms have one-celled body..... (T)

(b) Muscle cells are branched..... (T)

(c) The basic living unit of an organism is an organ..... (F)

(d) Amoeba has irregular shape..... (T)

2. Make a sketch of the human nerve cell. What function do nerve cells perform?.

Answer:

Here is a sketch of a human nerve cell:

Sketch

Nerve cells, also called neurons, are specialized cells that transmit nerve impulses, allowing us to communicate with the world around us.

3. Write short notes on the following.

(a) Cytoplasm  

(a) Cytoplasm: It is the jelly-like substance that fills the cell and contains various organelles. It plays an important role in the cellular metabolism.

(b) Nucleus of a cell  

(b) Nucleus of a cell: It is the control center of the cell that contains genetic material in the form of DNA. It regulates the functions of the cell.

4. Which part of the cell contains organelles?  

Answer:

Organelles are found in the cytoplasm of the cell.

5. Make sketches of animal and plant cells. State three differences between them.  

Answer:

Sketches of animal and plant cells

Three differences between animal and plant cells are:

Plant cells have a cell wall made of cellulose, while animal cells do not.

Plant cells have chloroplasts for photosynthesis, while animal cells do not.

Plant cells have a large central vacuole, while animal cells have small or no vacuoles.

6. State the difference between eukaryotes and prokaryotes.

Answer:

Eukaryotes are cells that have a nucleus and membrane-bound organelles, while prokaryotes are cells that do not have a nucleus or membrane-bound organelles.

7. Where are chromosomes found in a cell? State their function.  

Answer:

Chromosomes are found in the nucleus of a cell. Their function is to carry genetic information in the form of DNA.

8. ‘Cells are the basic structural units of living organisms’. Explain.  

Answer:

Cells are the basic structural units of living organisms because they are the smallest entities that can carry out all the functions of life, including metabolism, growth, and reproduction. All living organisms are made up of one or more cells.

9. Explain why chloroplasts are found only in plant cells?  

Chloroplasts are found only in plant cells because they are involved in the process of photosynthesis, which is a unique feature of plants. Chloroplasts contain chlorophyll, a pigment that absorbs light energy and converts it into chemical energy, which is used to produce glucose from carbon dioxide and water.

10. Complete the crossword with the help of clues given below.

Across  

1. This is necessary for photosynthesis.  

3. Term for component present in the cytoplasm.

6. The living substance in the cell.

8. Units of inheritance present on the chromosomes.

Down  

1. Green plastids.

2. Formed by collection of tissues.

4. It separates the contents of the cell from the surrounding medium.

5. Empty structure in the cytoplasm.

7. A group of cells 

Answer:

Across

Chlorophyll

Organelle

Protoplasm

Genes

Down

Chloroplasts

Organ

Cell membrane

Vacuole

Tissue

Important Questions

1. Explain the importance of reproduction in organisms.

Answer:

Reproduction is important for the continuation of a species and to maintain genetic diversity. It ensures the survival and adaptation of organisms in changing environments.

2. Describe the process of fertilisation in human beings.

Answer:

In human beings, fertilisation occurs when the sperm from the male fuses with the egg released from the ovary of the female. This typically happens in the fallopian tube. The sperm penetrates the outer layer of the egg and fuses with the nucleus, forming a zygote.

3. Choose the most appropriate answer.

(a) Internal fertilisation occurs  

(i) in female body.

(ii) outside female body.

(iii) in male body.

(iv) outside male body.

Answer:

(a) Internal fertilisation occurs in female body.  

(b) A tadpole develops into an adult frog by the process of  

(i) fertilisation

(ii) metamorphosis

(iii) embedding

(iv) budding

Answer:

(b) A tadpole develops into an adult frog by the process of metamorphosis.  

(c) The number of nuclei present in a zygote is

(i) none

(ii) one

(iii) two

(iv) four

Answer:

(c) The number of nuclei present in a zygote is one.

4. Indicate whether the following statements are True (T) or False (F).

Answer:

(a) Oviparous animals give birth to young ones..... (False) 

(b) Each sperm is a single cell..... (True) 

(c) External fertilisation takes place in frog..... (False)

(d) A new human individual develops from a cell called gamete..... (False)

(e) Egg laid after fertilisation is made up of a single cell..... (True) 

(f) Amoeba reproduces by budding...... (False) 

(g) Fertilisation is necessary even in asexual reproduction..... (False) 

(h) Binary fission is a method of asexual reproduction..... (True) 

(i) A zygote is formed as a result of fertilisation..... (True)

(j) An embryo is made up of a single cell.....  (False) 

5. Give two differences between a zygote and a foetus.  

Answer:

A zygote is a single cell formed by the fusion of a sperm and an egg, while a foetus is a developing organism after the embryonic stage.  

A foetus is more complex and undergoes further development before birth.

6. Define asexual reproduction. Describe two methods of asexual reproduction in animals

Answer:

Asexual reproduction is the process of producing offspring without the involvement of gametes. Two methods of asexual reproduction in animals are budding, where a new individual grows from the body of the parent, and binary fission, where a single organism divides into two identical offspring.

7. In which female reproductive organ does the embryo get embedded?

Answer:

The embryo gets embedded in the uterus lining of the female reproductive organ.

8. What is metamorphosis? Give examples.  

Answer:

Metamorphosis is the process of transformation from an immature form to an adult form in insects and amphibians. Examples include the transformation of a caterpillar into a butterfly and the transformation of a tadpole into a frog.

9. Differentiate between internal fertilisation and external fertilisation

Answer:

Internal fertilisation occurs within the body of the female, while external fertilisation occurs outside the body of the female. Internal fertilisation is more common in terrestrial animals, while external fertilisation is more common in aquatic animals.

10. Complete the crossword puzzle using the hints given below.

Across  

1. The process of the fusion of the gametes.

6. The type of fertilisation in hen.

7. The term used for bulges observed on the sides of the body of hydra.

8. Eggs are produced here.

Down  

2. Sperms are produced in these male reproductive organs.

3. Another term for in vitro fertilisation.

4. These animals lay eggs.

5. A type of fission in amoeba.

Answer:

Across

The process of the fusion of the gametes - Fertilisation

The type of fertilisation in hen - Internal fertilisation

The term used for bulges observed on the sides of the body of hydra - Buds

Eggs are produced here - Ovaries

Down

2. Sperms are produced in these male reproductive organs - Testes

Another term for in vitro fertilisation - Test tube baby

These animals lay eggs - Oviparous

A type of fission in amoeba - Binary fission

Important Questions

1. What is the term used for chemical secretions of endocrine glands responsible for changes taking place in the body?

Answer:

The term used for chemical secretions of endocrine glands responsible for changes taking place in the body is- Hormones.

2. Define adolescence.

Answer:

Adolescence is the transitional period between childhood and adulthood, during which the body undergoes various physical, physiological and psychological changes.

3. What is menstruation? Explain.

Answer:

Menstruation is the shedding of the lining of the uterus along with blood and other materials from the female reproductive system that occurs approximately once a month in females who have reached puberty and have not become pregnant.

4. List changes in the body that take place at puberty.

Answer:

Changes that take place at puberty include growth spurt, development of secondary sexual characteristics, increased activity of sweat and sebaceous glands, development of sex organs, and changes in the voice.

5. Prepare a Table having two columns depicting names of endocrine glands and hormones secreted by them.

Answer:

Endocrine gland ……. Hormone

Pituitary gland ……. Growth hormone, follicle-stimulating hormone, luteinizing hormone

Thyroid gland ……. Thyroxine

Parathyroid gland ……. Parathyroid hormone

Pancreas ……. Insulin, glucagon

Adrenal gland ……. Adrenaline, cortisol

Testes (male) ……. Testosterone

Ovaries (female) ……. Estrogen, progesterone

6. What are sex hormones? Why are they named so? State their function

Answer:

Sex hormones are hormones that are produced by the gonads (testes in males and ovaries in females) and are responsible for the development of secondary sexual characteristics and the regulation of reproductive functions. They are named so because they play a crucial role in determining the sex of an individual. Their functions include the development of sex organs, regulation of menstrual cycle, and the development of secondary sexual characteristics such as facial hair, breast development, and deepening of the voice.

7. Choose the correct option.

(a) Adolescents should be careful about what they eat, because  

(i) proper diet develops their brains.

(ii) proper diet is needed for the rapid growth taking place in their body.

(iii) adolescents feel hungry all the time.

(iv) taste buds are well developed in teenagers 

Answer:

(a) (ii) proper diet is needed for the rapid growth taking place in their body.

(b) Reproductive age in women starts when their  

(i) menstruation starts.

(ii) breasts start developing.

(iii) body weight increases.

(iv) height increases.  

Answer:

(b) (i) menstruation starts.

(c) The right meal for adolescents consists of

(i) chips, noodles, coke.

(ii) chapati, dal, vegetables.

(iii) rice, noodles and burger.

(iv) vegetable cutlets, chips and lemon drink.

Answer:

(c) (ii) chapati, dal, vegetables.

8. Write notes on—

(a) Adam’s apple.  

Answer:

(a) Adam's apple is a prominent lump in the front of the throat that is formed by the thyroid cartilage during puberty in boys. It is more prominent in boys because their larynx grows larger, causing the cartilage to protrude outward, creating a visible bulge in the throat.

(b) Secondary sexual characters.  

(b) Secondary sexual characters are physical changes that occur during puberty, distinguishing males and females from each other. In boys, secondary sexual characteristics include the deepening of voice, facial hair growth, broadening of shoulders, and development of Adam's apple. In girls, secondary sexual characteristics include breast development, widening of hips, and the onset of menstruation.

(c) Sex determination in the unborn baby.  

(c) Sex determination in the unborn baby is determined by the presence or absence of the Y chromosome. If the baby has a Y chromosome, they will develop into a male. If the baby does not have a Y chromosome, they will develop into a female. This is determined at fertilization when the sperm containing either an X or Y chromosome fuses with the egg, which always carries an X chromosome.

9. Word game :

Use the clues to work out the words.  

Across  

3. Protruding voice box in boys

4. Glands without ducts

7. Endocrine gland attached to brain

8. Secretion of endocrine glands

9. Pancreatic hormone

10. Female hormone

Down  

1. Male hormone

2. Secretes thyroxine

3. Another term for teenage

5. Hormone reaches here through blood stream

6. Voice box

7. Term for changes at adolescence  

Answer:

Across

3. Adam's apple

Endocrine glands

Pituitary gland

Hormones

Insulin

Estrogen

Down

Testosterone

Thyroid gland

Adolescence

Target organs

Larynx

Puberty

Important Questions

1. Give two examples each of situations in which you push or pull to change the state of motion of objects.

Answer:

Two examples each of situations in which you push or pull to change the state of motion of objects are:

Pushing a swing to make it move forward or pulling it back to slow down or stop it.

Pushing a football to make it move forward or pulling it back to change its direction.

2. Give two examples of situations in which applied force causes a change in the shape of an object.

Answer:

Two examples of situations in which applied force causes a change in the shape of an object are:

Compressing a spring by pushing on it or stretching it by pulling on it.

Squeezing a rubber ball to change its shape or pulling on a piece of clay to make it longer.

3. Fill in the blanks in the following statements.

(a) To draw water from a well we have to __pull__ at the rope.

(b) A charged body __attracts__ an uncharged body towards it.

(c) To move a loaded trolley we have to __push__ it.

(d) The north pole of a magnet __repels__ the north pole of another magnet.

4. An archer stretches her bow while taking aim at the target. She then releases the arrow, which begins to move towards the target. Based on this information fill up the gaps in the following statements using the following terms.

muscular, contact, non-contact, gravity, friction, shape, attraction  

Answer:

(a) To stretch the bow, the archer applies a force that causes a change in its __shape__.

(b) The force applied by the archer to stretch the bow is an example of __muscular__ force.

(c) The type of force responsible for a change in the state of motion of the arrow is an example of a __ non-contact___ force.

(d) While the arrow moves towards its target, the forces acting on it are due to ___gravity__ and that due to ___friction__ of air.

5. In the following situations identify the agent exerting the force and the object on which it acts.

State the effect of the force in each case.  

Answers:

(a) Squeezing a piece of lemon between the fingers to extract its juice.  

(a) Agent exerting the force: Fingers

Object on which it acts: Lemon

Effect of the force: Extracts juice from the lemon.

(b) Taking out paste from a toothpaste tube.  

(b) Agent exerting the force: Hand

Object on which it acts: Toothpaste tube

Effect of the force: Causes toothpaste to come out of the tube.

(c) A load suspended from a spring while its other end is on a hook fixed to a wall.

(c) Agent exerting the force: Load

Object on which it acts: Spring

Effect of the force: Stretches the spring.

(d) An athlete making a high jump to clear the bar at a certain height  

(d) Agent exerting the force: Athlete's body

Object on which it acts: Bar

Effect of the force: Overcomes the force of gravity to clear the bar.

6. A blacksmith hammers a hot piece of iron while making a tool. How does the force due to hammering affect the piece of iron?

Answer:

The force due to hammering causes the piece of iron to change its shape and become flat or thinner. This is an example of a contact force.

7. An inflated balloon was pressed against a wall after it has been rubbed with a piece of synthetic cloth. It was found that the balloon sticks to the wall. What force might be responsible for the attraction between the balloon and the wall?

Answer:

The force responsible for the attraction between the balloon and the wall is an electrostatic force. When the balloon is rubbed with a piece of synthetic cloth, it becomes charged and attracts the opposite charges present on the wall, causing it to stick to the wall.

8. Name the forces acting on a plastic bucket containing water held above ground level in your hand. Discuss why the forces acting on the bucket do not bring a change in its state of motion.

Answer:

The forces acting on a plastic bucket containing water held above ground level in your hand are the force of gravity pulling the bucket downwards, and the force exerted by your hand upwards to counteract the force of gravity. The net force on the bucket is zero, as the forces acting on it are balanced. This is why the forces acting on the bucket do not bring a change in its state of motion.

9. A rocket has been fired upwards to launch a satellite in its orbit. Name the two forces acting on the rocket immediately after leaving the launching pad.  

Answer:

The two forces acting on the rocket immediately after leaving the launching pad are the force of gravity pulling the rocket downwards, and the force of thrust acting upwards from the rocket engines. The force of thrust is greater than the force of gravity, causing the rocket to move upwards and accelerate.

10. When we press the bulb of a dropper with its nozzle kept in water, air in the dropper is seen to escape in the form of bubbles. Once we release the pressure on the bulb, water gets filled in the dropper.

The rise of water in the dropper is due to  

(a) pressure of water.  

(b) gravity of the earth.  

(c) shape of rubber bulb.

(d) atmospheric pressure.  

Answer:

The rise of water in the dropper is due to atmospheric pressure. When the bulb of the dropper is pressed, the air inside is compressed, increasing its pressure. This increased pressure pushes the water out of the dropper. When the pressure on the bulb is released, the pressure inside the dropper decreases, causing the atmospheric pressure to push the water back into the dropper.

Important Questions

1. Fill in the blanks.

(a) Friction opposes the __motion___ between the surfaces in contact

with each other.

(b) Friction depends on the__ nature___ of surfaces.

(c) Friction produces __heat__.

(d) Sprinkling of powder on the carrom board __reduces___ friction.

(e) Sliding friction is ___less___ than the static friction.

2. Four children were asked to arrange forces due to rolling, static and sliding frictions in a decreasing order. Their arrangements are given below. Choose the correct arrangement.

(a) rolling, static, sliding  

(b) rolling, sliding, static  

(c) static, sliding, rolling

(d) sliding, static, rolling

Answer:

The correct arrangement is  

(b) rolling, sliding, static

3. Alida runs her toy car on dry marble floor, wet marble floor, newspaper and towel spread on the floor. The force of friction acting on the car on different surfaces in increasing order will be

(a) wet marble floor, dry marble floor, newspaper and towel.  

(b) newspaper, towel, dry marble floor, wet marble floor.  

(c) towel, newspaper, dry marble floor, wet marble floor.

(d) wet marble floor, dry marble floor, towel, newspaper

Answer:

Alida runs her toy car on dry marble floor, wet marble floor, newspaper and towel spread on the floor. The force of friction acting on the car on different surfaces in increasing order will be

(d) wet marble floor, dry marble floor, towel, newspaper

4. Suppose your writing desk is tilted a little. A book kept on it starts sliding down. Show the direction of frictional force acting on it.

Answer:

The direction of frictional force acting on the book is opposite to the direction of motion, i.e. upwards along the plane of the desk.

5. You spill a bucket of soapy water on a marble floor accidentally. Would it make it easier or more difficult for you to walk on the floor? Why?

Answer:

It would make it more difficult to walk on the floor because the soap reduces the friction between the floor and the sole of the shoe, making it slippery.

6. Explain why sportsmen use shoes with spikes.

Answer:

Sportsmen use shoes with spikes to increase the friction between their shoes and the ground, which helps them to run faster and have better control over their movements.

7. Iqbal has to push a lighter box and Seema has to push a similar heavier box on the same floor. Who will have to apply a larger force and why?  

Answer:

Iqbal has to push a lighter box and Seema has to push a similar heavier box on the same floor. Who will have to apply a larger force and why?

Seema will have to apply a larger force because the force of friction between the heavier box and the floor will be greater than that between the lighter box and the floor.

8. Explain why sliding friction is less than static friction.

Answer:

Sliding friction is less than static friction because the irregularities on the surface of two objects in contact interlock more firmly when they are at rest relative to each other, creating a larger force of friction.

9. Give examples to show that friction is both a friend and a foe.

Answer:

Friction is a friend because it helps us to walk, write, and hold things. It also enables us to stop vehicles and control their speed.  

Friction is a foe because it causes wear and tear of moving parts, reduces efficiency, and generates heat in machines.

10. Explain why objects moving in fluids must have special shapes.

Answer:  

Objects moving in fluids must have special shapes to reduce the frictional force acting on them. Streamlined shapes, like those of fish or airplanes, help to reduce drag and increase speed.

Important Questions

1. Choose the correct answer. Sound can travel through.

(a) gases only  

(b) solids only  

(c) liquids only

(d) solids, liquids and gases

Answer:

(d) solids, liquids and gases

2. Voice of which of the following is likely to have minimum frequency?

(a) Baby girl  

(b) Baby boy  

(c) A man

(d) A woman

Answer:

(c) A man

3. In the following statements, tick ‘T’ against those which are true, and ‘F’ against those which are false.

(a) Sound cannot travel in vacuum..... (True) 

(b) The number of oscillations per second of a vibrating object is called its time period..... (True) 

(c) If the amplitude of vibration is large, sound is feeble..... (False) 

(d) For human ears, the audible range is 20 Hz to 20,000 Hz..... (True)

(e) The lower the frequency of vibration, the higher is the pitch..... (False) 

(f) Unwanted or unpleasant sound is termed as music..... (False) 

(g) Noise pollution may cause partial hearing impairment..... (True)  

4. Fill in the blanks with suitable words.

(a) Time taken by an object to complete one oscillation is called __Time period___.

(b) Loudness is determined by the __Amplitude____ of vibration.

(c) The unit of frequency is __Hertz (Hz)____.

(d) Unwanted sound is called ___Noise___.

(e) Shrillness of a sound is determined by the __Frequency__ of vibration  

5. A pendulum oscillates 40 times in 4 seconds. Find its time period and frequency. 

Answer:

Time period = 0.1 seconds, Frequency = 10 Hz

6. The sound from a mosquito is produced when it vibrates its wings at an average rate of 500 vibrations per second. What is the time period of the vibration?

Answer:

Time period = 0.002 seconds

7. Identify the part which vibrates to produce sound in the following instruments.

(a) Dholak  

(b) Sitar  

(c) Flute

Answer:  

(a) Dholak…...(a) Membrane

(b) Sitar…….. (b) String   

(c) Flute ……. (c) Air column

8. What is the difference between noise and music? Can music become noise sometimes?  

Answer:

Noise is an unwanted, unpleasant or disturbing sound, whereas music is a pleasing arrangement of sounds. Music can become noise if it is too loud or unpleasant to the listener.

9. List sources of noise pollution in your surroundings.

Answer:

Sources of noise pollution can include traffic, construction sites, factories, loud music, barking dogs, and aircraft noise.

10. Explain in what way noise pollution is harmful to human

Answer:

Noise pollution can lead to hearing impairment, high blood pressure, sleep disturbance, stress, and other health issues.

11. Your parents are going to buy a house. They have been offered one on the roadside and another three lanes away from the roadside. Which house would you suggest your parents should buy? Explain your answer.

Answer:

It is recommended to buy a house three lanes away from the roadside as it will be less exposed to noise pollution, which can be harmful to health.

12. Sketch larynx and explain its function in your own words.

Answer:

Sketch

Larynx is a part of the throat that contains the vocal cords. It helps in producing sound by vibrating the vocal cords when air passes through them.

13. Lightning and thunder take place in the sky at the same time and at the same distance from us. Lightning is seen earlier and thunder is heard later. Can you explain why?  

Answer:

Light travels faster than sound, so lightning is seen earlier than thunder is heard. The distance between the lightning and thunder can be calculated by counting the seconds between seeing the lightning and hearing the thunder and dividing by five.

Important Questions

1. Fill in the blanks.

(a) Most liquids that conduct electricity are solutions of ___acids___, _bases__, and __salts__.

(b) The passage of an electric current through a solution causes __chemical effects__.

(c) If you pass current through copper sulphate solution, copper gets deposited on the plate connected to the __positive__ terminal of the battery.

(d) The process of depositing a layer of any desired metal on another material by means of electricity is called __electroplating__.

2. When the free ends of a tester are dipped into a solution, the magnetic needle shows deflection. Can you explain the reason?

Answer:  

The reason behind the deflection of the magnetic needle of a tester when its free ends are dipped into a solution is that the solution conducts electricity due to the presence of ions. When the tester is dipped into the solution, it completes an electric circuit, and an electric current starts flowing through the solution. This causes a chemical reaction at the electrodes, leading to the generation of ions. The movement of these ions towards the electrodes causes a magnetic field, which deflects the magnetic needle of the tester. The direction of deflection depends on the type of ions present in the solution.

3. Name three liquids, which when tested in the manner shown in Fig.14.9, may cause the magnetic needle to deflect.

Answer:

The method shown in Fig. 14.9 involves dipping the free ends of a tester into a liquid to test its conductivity. If a liquid contains ions and is able to conduct electricity, it may cause the magnetic needle to deflect.  

Here are three examples of liquids that may cause the magnetic needle to deflect:

Saltwater:Saltwater contains ions of sodium and chloride, which can conduct electricity and cause the magnetic needle to deflect.

Vinegar:Vinegar is a solution of acetic acid, which contains ions and can conduct electricity. Hence, it can cause the magnetic needle to deflect.

Lemon juice: Lemon juice is acidic and contains ions of hydrogen and citrate, which can conduct electricity and cause the magnetic needle to deflect.

4. The bulb does not glow in the setup shown in Fig.14.10. List the possible reasons. Explain your answer.  

Answer:

The solution is not conductive

5. A tester is used to check the conduction of electricity through two liquids, labelled A and B. It is found that the bulb of the tester glows brightly for liquid A while it glows very dimly for liquid B. You would conclude that

(i) liquid A is a better conductor than liquid B.

(ii) liquid B is a better conductor than liquid A.

(iii) both liquids are equally conducting.

(iv) conducting properties of liquid cannot be compared in this manner.  

Answer:

(i) liquid A is a better conductor than liquid B.

6. Does pure water conduct electricity? If not, what can we do to make it conducting?  

Answer:

Pure water is a poor conductor of electricity because it does not contain any free ions that can carry the electric charge. To make it conducting, we can add some soluble salts or acids to the water, which will dissociate into ions and increase the conductivity of the solution.

7. In case of a fire, before the firemen use the water hoses, they shut off the main electrical supply for the area. Explain why they do this.

Answer:

Water is a good conductor of electricity, and if it comes into contact with live electrical wires or equipment, it can create a dangerous situation for the firemen and everyone else around. By shutting off the main electrical supply for the area, the firemen eliminate the risk of electrocution and can use the water hoses safely to put out the fire.

8. A child staying in a coastal region tests the drinking water and also the seawater with his tester. He finds that the compass needle deflects more in the case of seawater. Can you explain the reason? 

Answer:

Seawater contains a higher concentration of dissolved salts and ions than drinking water, which makes it a better conductor of electricity. When the child tests the seawater and drinking water with the tester, the higher conductivity of the seawater causes a greater deflection of the compass needle.

9. Is it safe for the electrician to carry out electrical repairs outdoors during heavy downpour? Explain.

Answer:

It is not safe for an electrician to carry out electrical repairs outdoors during heavy downpour because water is a good conductor of electricity, and the risk of electrocution is high when working with live electrical wires or equipment in wet conditions.

10. Paheli had heard that rainwater is as good as distilled water. So she collected some rainwater in a clean glass tumbler and tested it using a tester. To her surprise she found that the compass needle showed deflection. What could be the reasons?

Answer:

Rainwater is not completely pure and contains dissolved gases and ions picked up from the atmosphere. These impurities increase the conductivity of the rainwater, causing the deflection of the compass needle when tested with a tester.

11. Prepare a list of objects around you that are electroplated.

Answer:  

Objects around us that are electroplated include jewelry (e.g., gold-plated or silver-plated), chrome-plated car parts, plated kitchen and bathroom fixtures, and plated hardware and tools.

12. The process that you saw in Activity 14.7 is used for purification of copper. A thin plate of pure copper and a thick rod of impure copper are used as electrodes. Copper from impure rod is sought to be transferred to the thin copper plate. Which electrode should be attached to the positive terminal of the battery and why?  

Answer:

The pure copper plate should be attached to the negative terminal of the battery, and the impure copper rod should be attached to the positive terminal. This is because during electrolysis, positive ions are attracted to the negative electrode (cathode), where they gain electrons and are reduced to form a metal deposit. In this case, the copper ions from the impure rod will be attracted to the pure copper plate and deposited on it, while the impurities will remain on the impure rod.

Important Questions

1. Which of the following cannot be charged easily by friction?

(a) A plastic scale  

(b) A copper rod  

(c) An inflated balloon

(d) A woollen cloth.  

Answer:

(b) A copper rod

2. When a glass rod is rubbed with a piece of silk cloth the rod

(a) and the cloth both acquire positive charge.  

(b) becomes positively charged while the cloth has a negative charge.  

(c) and the cloth both acquire negative charge.

(d) becomes negatively charged while the cloth has a positive charge

Answer

(b) becomes positively charged while the cloth has a negative charge.

3. Write T against true and F against false in the following statements.

Answer:

(a) Like charges attract each other (F)

(b) A charged glass rod attract a charged plastic straw (T)

(c) Lightning conductor cannot protect a building from lightning (F)

(d) Earthquakes can be predicted in advance (F)

4. Sometimes, a crackling sound is heard while taking off a sweater during winters. Explain.

Answer:

The crackling sound heard while taking off a sweater during winters is due to the friction between the sweater and the body. This friction causes the transfer of electrons from one object to another, leading to the buildup of static electricity. When we remove the sweater, the accumulated charge on it gets discharged in the form of a spark, producing the crackling sound.

5. Explain why a charged body loses its charge if we touch it with our hand.  

Answer:

A charged body loses its charge when we touch it with our hand because our body is a good conductor of electricity. When we touch a charged body, the charge flows through our body to the ground, neutralizing the charge on the body.

6. Name the scale on which the destructive energy of an earthquake is measured. An earthquake measures 3 on this scale. Would it be recorded by a seismograph? Is it likely to cause much damage?

Answer:

The destructive energy of an earthquake is measured on the Richter scale. An earthquake measuring 3 on the Richter scale would be recorded by a seismograph but is not likely to cause much damage.

7. Suggest three measures to protect ourselves from lightning.

Answer:

Three measures to protect ourselves from lightning are:

Stay indoors during a thunderstorm.

Avoid taking shelter under trees or standing near metal objects like poles, fences, or wires.

If caught outside during a thunderstorm, crouch down with your feet together and your head tucked in.

8. Explain why a charged balloon is repelled by another charged balloon whereas an uncharged balloon is attracted by another charged balloon?  

Answer:

A charged balloon is repelled by another charged balloon because both have the same type of charge, either positive or negative. An uncharged balloon is attracted by a charged balloon because the charged balloon polarizes the atoms in the uncharged balloon, creating an attractive force between them.

9. Describe with the help of a diagram an instrument which can be used to detect a charged body.  

Answer:

An electroscope is an instrument that can be used to detect a charged body. It consists of a metal rod with two thin metal leaves attached to the bottom. When a charged object is brought near the metal rod, the leaves acquire the same charge and repel each other, indicating the presence of a charged body.

10. List three states in India where earthquakes are more likely to strike.  

Answer:

Three states in India where earthquakes are more likely to strike are:

Uttarakhand

Himachal Pradesh

Jammu and Kashmir

11. Suppose you are outside your home and an earthquake strikes. What precaution would you take to protect yourself?  

Answer:

If an earthquake strikes while outside, some precautions that can be taken to protect oneself are:

Move away from buildings, trees, and other tall objects.

Drop to the ground and stay there until the shaking stops.

Cover your head with your arms to protect yourself from falling debris.

12. The weather department has predicted that a thunderstorm is likely to occur on a certain day. Suppose you have to go out on that day. Would you carry an umbrella? Explain  

Answer:

It is not advisable to carry an umbrella during a thunderstorm because umbrellas are made of metal, which can attract lightning. If struck by lightning, carrying an umbrella can lead to serious injury or even death.

Important Questions

1. Suppose you are in a dark room. Can you see objects in the room? Can you see objects outside the room. Explain.

Answer:  

No, we cannot see objects in a dark room because there is no source of light to reflect off the objects and enter our eyes. We can see objects outside the room if there is a source of light outside the room and it enters the room through a window or an open door.

2. Differentiate between regular and diffused reflection. Does diffused reflection mean the failure of the laws of reflection?

Answer:  

Regular reflection occurs when parallel rays of light fall on a smooth and shiny surface and the reflected rays remain parallel to each other. Diffused reflection occurs when parallel rays of light fall on an uneven or rough surface and the reflected rays scatter in different directions.

No, diffused reflection does not mean the failure of the laws of reflection. The laws of reflection are still obeyed in diffused reflection, but the surface is uneven, so the reflected rays scatter in different directions.

3. Mention against each of the following whether regular or diffused reflection will take place when a beam of light strikes. Justify your answer in each case.

(a) Polished wooden table  

(b) Chalk powder  

(c) Cardboard surface

(d) Marble floor with water spread over it

(e) Mirror  

(f) Piece of paper  

Answer:

(a) Polished wooden table - Regular reflection will take place because the surface is smooth and shiny.

(b) Chalk powder- Diffused reflection will take place because the surface is uneven.

(c) Cardboard surface - Diffused reflection will take place because the surface is uneven.

(d) Marble floor with water spread over it - Diffused reflection will take place because the surface is uneven due to the presence of water.

(e) Mirror - Regular reflection will take place because the surface is smooth and shiny.

(f) Piece of paper - Diffused reflection will take place because the surface is uneven.

4. State the laws of reflection.

Answer:  

The laws of reflection are:

(i) The angle of incidence is equal to the angle of reflection.

(ii) The incident ray, the reflected ray and the normal to the reflecting surface at the point of incidence, all lie in the same plane.

5. Describe an activity to show that the incident ray, the reflected ray and the normal at the point of incidence lie in the same plane.

Answer:

Take a drawing board, fix a white paper on it and draw a straight line XY on it. Fix a plane mirror along the line XY. Take a protractor and draw a perpendicular line at the midpoint of line XY. This line will be the normal to the mirror. Take a ray box and direct a ray of light at the mirror at an angle of incidence, say 30 degrees, with the normal. Mark the incident ray as IO. The ray after reflection will be marked as OR. Draw a line at the back of the mirror along OR. Remove the mirror and measure the angle POR. It will be found to be 60 degrees, which is equal to the angle of incidence. This proves that the incident ray, the reflected ray and the normal at the point of incidence lie in the same plane.

6. Fill in the blanks in the following.

(a) A person 1 m in front of a plane mirror seems to be __2 m__ away from his image.

(b) If you touch your __left__ ear with right hand in front of a plane mirror it will be seen in the mirror that your right ear is touched with __left hand___.  

(c) The size of the pupil becomes ___larger___ when you see in dim light.

(d) Night birds have __more___ cones than rods in their eyes.

7. Angle of incidence is equal to the angle of reflection.

(a) Always  

(b) Sometimes  

(c) Under special conditions

(d) Never 

Answer:  

(a) Always

8. Image formed by a plane mirror is

(a) virtual, behind the mirror and enlarged.  

(b) virtual, behind the mirror and of the same size as the object.  

(c) real at the surface of the mirror and enlarged.

(d) real, behind the mirror and of the same size as the object.

Answer:

(b) virtual, behind the mirror and of the same size as the object.

9. Describe the construction of a kaleidoscope.

Answer:

Sketch

A kaleidoscope consists of three rectangular mirrors, arranged in the form of a prism, with the reflecting surfaces inclined to each other at an angle of 60 degrees.  

At one end of the mirrors, there is a hole for the viewer to look through. At the other end, there is a chamber containing small pieces of coloured glass or other objects.  

When the chamber is rotated, the objects tumble around, producing a constantly changing symmetrical pattern of reflections which can be observed through the viewing hole.

10. Draw a labelled sketch of the human eye.

Answer:

Sketch of Human Eye

Labelled diagram of the human eye:

Cornea

Iris

Pupil

Lens

Ciliary muscles

Suspensory ligaments

Retina

Optic nerve

Vitreous humor

Aqueous humor

Sclera

11. Gurmit wanted to perform Activity 16.8 using a laser torch. Her teacher advised her not to do so. Can you explain the basis of the teacher’s advise?  

Answer:  

Activity 16.8 involves passing a narrow beam of light through a rectangular glass slab and observing the path of the beam of light. If a laser torch is used instead of a light source, the beam of light will be highly concentrated and powerful.  

If not handled properly, it can cause damage to the eyes, which is why Gurmit's teacher advised her not to use a laser torch for this activity.

12. Explain how you can take care of your eyes.

Answer:  

We can take care of our eyes by following ways:

By eating a balanced diet rich in vitamins and minerals, especially those that promote eye health like Vitamin A, C, and E.

By avoiding looking directly at the sun or bright lights.

By taking regular breaks when doing activities that require prolonged focus such as reading, using the computer or mobile phone.

By practising good hygiene by washing your hands regularly and not touching your eyes with dirty hands.

By wearing sunglasses when going outside to protect your eyes from harmful UV rays.

We should get regular eye checkups to detect any eye problems early and treat them promptly.

13. What is the angle of incidence of a ray if the reflected ray is at an angle of 90° to the incident ray?

Answer:  

If the reflected ray is at an angle of 90° to the incident ray, then the angle of incidence is 45°. This is because according to the law of reflection, the angle of incidence is equal to the angle of reflection, and when the reflected ray is at 90°, the incident ray and reflected ray make a 90° angle together. Since the sum of the angles in a triangle is 180°, the incident angle must be half of the remaining 90°, which is 45°.

14. How many images of a candle will be formed if it is placed between two parallel plane mirrors separated by 40 cm?

Answer:

If a candle is placed between two parallel plane mirrors separated by 40 cm, an infinite number of images of the candle will be formed. However, only a finite number of images will be visible to an observer as the intensity of light decreases with each reflection.

15. Two mirrors meet at right angles. A ray of light is incident on one at an angle of 30° as shown in Fig. 16.19. Draw the reflected ray from the second mirror  

Answer:

The reflected ray from the second mirror can be drawn by using the law of reflection. The angle of incidence is equal to the angle of reflection, and the reflected ray is on the opposite side of the normal as the incident ray. The final image will depend on the exact angle of incidence and the orientation of the mirrors.

16. Boojho stands at A just on the side of a plane mirror as shown in Fig. 16.20. Can he see himself in the mirror? Also can he see the image of objects situated at P, Q and R? 

Answer:

Boojho can see his image in the mirror as long as he is within the field of view of the mirror. The image of objects at P and Q can also be seen in the mirror, but the image of R will be obstructed by the mirror itself.

17. (a) Find out the position of the image of an object situated at A in the plane mirror (Fig. 16.21).

Answer:

(a) The position of the image of an object situated at A in the plane mirror can be found by extending the imaginary line from the object to the mirror and then reflecting it back along the same path. The image will be located behind the mirror, at the same distance as the object in front of the mirror.

(b) Can Paheli at B see this image?  

(b) Paheli at B cannot see this image as she is not in the line of sight between the object and the mirror.

(c) Can Boojho at C see this image?  

(c) Boojho at C can see this image as he is in the line of sight between the object and the mirror.

(d) When Paheli moves from B to C, where does the image of A move?  

(d) When Paheli moves from B to C, the image of A remains in the same position as it is behind the mirror and does not move. However, the observer's perspective changes, causing the image to appear in a different location.

Important Questions

Choose the correct answer in Questions 1-3.  

1. Which of the following is NOT a member of the solar system?

(a) An asteroid  

(b) A satellite  

(c) A constellation

(d) A comet

Answer:

(c) A constellation is not a member of the solar system. It is a group of stars that form a recognizable pattern or shape.

2. Which of the following is NOT a planet of the sun?

(a) Sirius  

(b) Mercury  

(c) Saturn

(d) Earth

Answer:

(a) Sirius is not a planet of the sun. It is a star located in the Canis Major constellation.

3. Phases of the moon occur because

(a) we can see only that part of the moon which reflects light towards us.  

(b) our distance from the moon keeps changing.  

(c) the shadow of the Earth covers only a part of the moon’s surface.

(d) the thickness of the moon’s atmosphere is not constant.

Answer:

(a) we can see only that part of the moon which reflects light towards us.

4. Fill in the blanks.

(a) The planet which is farthest from the Sun is _Neptune____ .  

(b) The planet which appears reddish in colour is ___Mars____ .  

(c) A group of stars that appear to form a pattern in the sky is known as a ___constellation___ .

(d) A celestial body that revolves around a planet is known as __satellite___.

(e) Shooting stars are actually not ____stars____.  

(f) Asteroids are found between the orbits of ___Mars___ and __Jupiter__ .   

5. Mark the following statements as true (T) or false (F).

(a) Pole star is a member of the solar system. (False)  

(b) Mercury is the smallest planet of the solar system. (True)  

(c) Uranus is the farthest planet in the solar system. (False)

(d) INSAT is an artificial satellite. (True)

(e) There are nine planets in the solar system. (False )  

(f) Constellation Orion can be seen only with a telescope. (False)  

6. Match items in column A with one or more items in column B.

Column A….. Column B  

(i) Inner planets ….. (a) Saturn

(ii) Outer planets ….. (b) Pole star

(iii) Constellation ….. (c) Great Bear

(iv) Satellite of the Earth ….. (d) Moon (e) Earth (f) Orion (g) Mars.

Answer:

Column A …..  Column B

(i) Inner planets - (e) Earth, (g) Mars

(ii) Outer planets - (a) Saturn

(iii) Constellation - (c) Great Bear, (f) Orion

(iv) Satellite of the Earth - (d) Moon

7. In which part of the sky can you find Venus if it is visible as an evening star?

Answer:

Venus, when visible as an evening star, can be found in the western part of the sky after sunset.

8. Name the largest planet of the solar system.

Answer:

Jupiter is the largest planet of the solar system.

9. What is a constellation? Name any two constellations.

Answer:

A constellation is a group of stars that form a recognizable pattern or shape as seen from the Earth. Two constellations are:

• Ursa Major (also known as the Great Bear or Big Dipper)
• Orion (also known as hunter constellation)

10. Draw sketches to show the relative positions of prominent stars in (a) Ursa Major and (b) Orion

Answer:

Sketch

11. Name two objects other than planets which are members of the solar system.

Answer:

Two objects other than planets which are members of the solar system are comets and asteroids.

12. Explain how you can locate the Pole Star with the help of Ursa Major.

Answer:

The two end stars of the bowl of the Ursa Major constellation are called the pointer stars. An imaginary line joining these two stars and extending towards the north leads to the Pole Star. Thus, by locating the Ursa Major and using the pointer stars, we can locate the Pole Star.

13. Do all the stars in the sky move? Explain.

Answer:

Yes, all the stars in the sky move. This movement is due to the rotation of the Earth on its axis. However, the movement of the stars is not noticeable to us because of the vast distances involved.

14. Why is the distance between stars expressed in light years? What do you understand by the statement that a star is eight light years away from the Earth?

Answer:

The distance between stars is expressed in light years because it is an extremely large distance and expressing it in kilometers or miles would result in very large numbers. A light year is the distance traveled by light in one year (about 9.46 trillion kilometers or 5.88 trillion miles).

When we say that a star is eight light years away from the Earth, it means that the light from that star takes eight years to reach the Earth. This also means that the information we receive from that star, such as its brightness, temperature, and composition, is eight years old.

15. The radius of Jupiter is 11 times the radius of the Earth. Calculate the ratio of the volumes of Jupiter and the Earth. How many Earths can Jupiter accomodate?  

Answer:

The ratio of the volumes of Jupiter and the Earth can be calculated using the formula for the volume of a sphere, which is given by V = 4/3 πr³, where r is the radius of the sphere.

The radius of Jupiter = 11 times the radius of the Earth

Therefore, the volume of Jupiter = (4/3)π(11r)³ = (4/3)π(1331r³) = 523.6 times the volume of the Earth = 523.6 : 1

Since Jupiter's volume is 523.6 times that of the Earth, it can accommodate 523.6 Earths.

16. Boojho made the following sketch (Fig. 17.29) of the solar system. Is the sketch correct? If not, correct it.

Answer:

The sketch made by Boojho is not correct. The correct sketch of the solar system is given below:

Sun → Mercury → Venus → Earth → Mars → Asteroid Belt → Jupiter → Saturn → Uranus → Neptune → Kuiper Belt → Oort Cloud.

In the correct sketch, the planets are arranged in the order of their distance from the Sun.

Important Questions

1. What are the different ways in which water gets contaminated?

Answer:

Water can get contaminated by various ways such as:

Industrial waste and chemicals being disposed of in water bodies

Domestic waste, sewage, and garbage being dumped into water bodies

Use of pesticides and fertilizers in agricultural fields contaminating water sources

Leakage and seepage of underground tanks, landfills, and waste disposal sites into groundwater

Natural pollutants such as arsenic and fluoride in the groundwater in some areas

2. At an individual level, how can you help reduce air pollution?

Answer:

At an individual level, one can help reduce air pollution by:

Reducing the usage of private vehicles and choosing public transport or carpooling instead

Using energy-efficient appliances and bulbs to reduce the consumption of electricity

Avoiding the burning of garbage and leaves, and instead disposing of them properly

Planting trees and supporting afforestation drives

Using eco-friendly products and avoiding the use of plastic

3. Clear, transparent water is always fit for drinking. Comment.

Answer:

Clear, transparent water is not always fit for drinking as it may contain harmful pollutants such as bacteria, viruses, and chemicals which are not visible to the naked eye. Water needs to be treated properly before consumption to remove these contaminants.

4. You are a member of the municipal body of your town. Make a list of measures that would help your town to ensure the supply of clean water to all its residents.

Answer:

Measures that can be taken to ensure the supply of clean water to all residents include:

Regular cleaning and maintenance of water storage tanks and supply lines

Treating water before supply to remove harmful contaminants

Regular testing of water quality and making the results publicly available

Encouraging and promoting rainwater harvesting

Creating awareness among citizens about the importance of water conservation and proper disposal of waste

5. Explain the differences between pure air and polluted air.

Answer:

Pure air refers to the air that is free from any harmful pollutants and is safe for breathing. Polluted air, on the other hand, contains various harmful pollutants such as particulate matter, nitrogen oxides, sulfur dioxide, and carbon monoxide which can have negative effects on human health and the environment

6. Explain circumstances leading to acid rain. How does acid rain affect us?

Answer:

Acid rain is formed due to the presence of pollutants like sulphur dioxide (SO2) and nitrogen oxides (NOx) in the atmosphere. These pollutants are released from burning fossil fuels like coal and oil, industrial processes, and vehicular emissions. When these pollutants react with water, oxygen, and other chemicals in the atmosphere, they form acidic compounds like sulphuric acid (H2SO4) and nitric acid (HNO3). These acidic compounds then fall on the earth’s surface as acid rain. Acid rain can affect aquatic life, damage crops, forests, and buildings, and also cause respiratory problems in humans.

7. Which of the following is __not__a greenhouse gas?

(a) Carbon dioxide  

(b) Sulphur dioxide  

(c) Methane

(d) Nitrogen

Answer:

(d) Nitrogenis not a greenhouse gas. The most common greenhouse gases include carbon dioxide (CO2), methane (CH4), and water vapor (H2O), which trap heat in the Earth's atmosphere and contribute to global warming. Nitrogen (N2) is a gas that makes up 78% of the Earth's atmosphere, but it does not have the ability to trap heat and thus is not considered a greenhouse gas.

8. Describe the ‘Green House Effect’ in your own words.  

Answer:

The Greenhouse Effect is a natural process that occurs when certain gases in the Earth's atmosphere, such as carbon dioxide, water vapour, and methane, trap heat from the sun's radiation, which warms the planet's surface. These gases act like a blanket, trapping heat and preventing it from escaping back into space. Without the Greenhouse Effect, the Earth would be too cold to support life as we know it. However, human activities, such as burning fossil fuels and deforestation, are increasing the levels of these greenhouse gases in the atmosphere, causing the Earth's temperature to rise, and leading to global warming.

9. Prepare a brief speech on global warming. You have to deliver the speech in your class.

Answer:

(My speech goes like this, also you may check the creative writing section for more details )

My Dear classmates, 

Today I want to talk to you about global warming. As we all know, the Earth's temperature is increasing at an alarming rate, and this is primarily due to human activities. Our dependence on fossil fuels like coal, oil, and gas, and our deforestation practices, are releasing enormous amounts of greenhouse gases like carbon dioxide and methane into the atmosphere, causing the planet to warm up. This warming is causing a range of problems, including melting ice caps, rising sea levels, increased frequency and intensity of extreme weather events, and the loss of biodiversity. It is crucial that we all take action to reduce our carbon footprint by making simple changes in our daily lives, such as reducing energy consumption, using public transport, and planting more trees. Let's all do our part to protect our planet for ourselves and future generations.

10. Describe the threat to the beauty of the Taj Mahal.

Answer:

The Taj Mahal, one of the world's most iconic and beautiful buildings, the threat to the beauty of the Taj Mahal is due to air pollution caused by the burning of fossil fuels and industries in the nearby areas. These activities release pollutants like sulphur dioxide and nitrogen oxides, which combine with moisture in the air to form acid rain. Acid rain corrodes the marble surface of the Taj Mahal and causes dis-colouration and degradation of the intricate carvings and inlay work.

11. Why does the increased level of nutrients in the water affect the survival of aquatic organisms?

Answer:

Increased levels of nutrients in the water, such as nitrogen and phosphorus from agricultural run-off and sewage discharge, lead to an excessive growth of algae and other aquatic plants. This is known as eutrophication and can lead to a decrease in the oxygen content of the water as the plants die and decompose. This creates an unfavourable environment for aquatic organisms, as they require oxygen to survive. Additionally, the excessive growth of plants can also block sunlight from reaching the bottom of the water body, affecting the survival of plants and animals that live there.

Important Questions