Friday, 4 April 2014

CBSE Class 10th (X) Science | All Chapters Exercises Solutions

This post contains links to solutions of all chapters for NCERT textbook of Science for Class 10th under CBSE. Each link for the chapter provides solutions to questions given in its main exercises including multiple choice questions, numericals, activities and in-text questions given after a main section to check the under standing of  the topic by students .
Chapter 1. Chemical Reactions And Equations | CBSE Class 10th Science | Solved Exercises 
 
Chapter 2. Acids, Bases and Salts |CBSE Class 10th Science | Solved Exercises

Chapter 3. Metals and Non-metals | CBSE Class 10th Science | Solved Exercises

Chapter 4. Carbon and its Compounds | Science |CBSE Class 10th | Solved Exercises
 
Chapter 5. Periodic Classification of Elements | CBSE Class 10th Science | Solved Exercises
 
Chapter 6. Life Processes | CBSE Class 10th Science | Solved Exercises

Chapter 7 : Control and Coordination | CBSE Class 10th Science | Solved Exercises

Chapter 8 : How do Organisms Reproduce? | CBSE Class 10th Science | Solved Exercises

Chapter 9 : Heredity and Evolution | Science | Class 10th - CBSE | Solved Exercises

Chapter 10. Light – Reflection and Refraction | Science | CBSE Class 10th |Solved Exercises

Chapter 11. The Human Eye and the Colourful World | Science |CBSE Class 10th | Solved Exercises
Chapter 12. Electricity | CBSE Class 10th | Science | Solved Exercises

Chapter 13. Magnetic Effects of Electric Current | Science CBSE Class 10th | Solved Exercises 
 
Chapter 14. Sources of Energy | CBSE Class 10th Science | Solved Exercises

Chapter 15. Our Environment | CBSE Class 10th Science | Solved Exercises

Chapter 16. Management of Natural Resources | CBSE Class 10th Science | Solved Exercises

Monday, 31 March 2014

Chapter 16. Management of Natural Resources | CBSE Class 10th Science | Solved Exercises

Intext Questions | Page 269 |Chapter 16. Management of Natural Resources | CBSE Class 10th Science |  

Question 1. What changes can you make in your habits to become more environment-friendly?

Answer. We can make certain positive changes in our habits to become more environment-friendly. We can follow the simple policy of the three R's i.e., Reduce, Reuse and Recycle
 Which simply means that for our living, we should minimise the consumption of products, services. and other usable resources to the extent possible. We should avoid unproductive and unnecessary consumption of product and resources. After primary usage, instead of discarding them as waste, we should try to reuse these products or resources for other possible secondary usages. After reuse, residual waste should be sent to recycling so that the exploitation of natural resources to meet ever increasing demand for new products, can be mininised. So, by adopting ourselves to few changes in our habits, We can make a substantial contribution to become more environment-friendly.

A fundamental principle for Management of  Natural Resources


Question 2. What would be the advantages of exploiting resources with short-term aims?

Answer. The advantages of exploiting resources with short-term aims will be in the form of high concentration and fast accumulation of capital or wealth for handful of rich and powerful people, without any accountability to rest of community and future generations.

Question 3. How would these advantages differ from the advantages of using a long term perspective in managing our resources?

Answer. Exploiting resources with short-term aim is just to make quick and huge profit by small number of people without any concern for rest of community, future generation , environment and nature. Where as, using resources with a long-term perspective is to extract the resources for the befit in a sustainable manner so that these will last for the generations to come and will not merely be exploited to the hilt for short term gains. This management should also ensure equitable distribution of resources so that all, and not just a handful of rich and powerful people, benefit from the development of these resources.

Question 4. Why do you think there should be equitable distribution of resources? What forces would be working against an equitable distribution of our resources?

Answer. The nature has provided abundant resources at the disposal of mankind on this planet without any discrimination. Excessive exploitation of these resources by some people will result in deprivation of these resource for others. This will not only result in ecological imbalance but also result in class struggle with in community for acquiring the depleting resource.
Handful of rich and powerful individuals or industrialists who extract these resource in unmindful way for undue large personal gain in short time, would be the forces, working against an equitable distribution of our resources

Intext Questions |Page 273 |Chapter 16. Management of Natural Resources | CBSE Class 10th Science |

Question 1. Why should we conserve forests and wildlife?

Answer. Forests are 'biodiversity hotspots'. One measure of the biodiversity of an area is the number of species found there. However, the range of different life forms (bacteria, fungi, ferns, flowering plants, nematodes, insects, bird, reptiles and so on) is also important. One of the main aims of conservation is to try and preserve the biodiversity we have inherited. Experiments and field studies suggest that a loss of diversity may lead to a loss of ecological stability.

Question 2. Suggest some approaches towards the conservation of forests.

Answer. Forest resources ought to be used in a manner that is both environmentally and developmentally sound.
In other words, while the environment is preserved, the befits of the controlled exploitation go to the local people, a process in which decentralized economic growth and ecological conservation go hand in hand.

Intext Questions |Page 276 |Chapter 16. Management of Natural Resources | CBSE Class 10th Science

Question 1. Find out about the traditional systems of water harvesting/management in your region.

Answer. Water harvesting is an age-old concept in India. Khadins, tanks and nadis in Rajasthan, bandharas and tals in Maharasthra, bundhis in Madhya Pradesh and Uttar Pardesh, ahars and pynes in Bihar, Kulhs in Himachal Pradesh, ponds in the Kandi belt of Jammu region, and eris (tanks) in Tamil Nadu, surangams in Kerela and kattas in Karnatka are some of the ancient water harvesting, including water conveyance, structures still in use.
In Rajasthan, khandis are more prevalent. First designed by the Paliwal Brahmins of jaisalmer, western Rajasthan in the 15the century, this system is still used in many parts of the state.
A khadin, also called a dhora is designed to harvest surface runoof water for agriculture. Its mains feature is a very long (100-300m) eastern embankment built across the lower hill slopes lying below gravely unplands.

The khadin system is based on the principal of harvesting rainwater on farmland and subsequent use of this water- saturated land for crop production. In largely level terrain, the water harvesting structures are mainly crescent shaped earthen embankments or low, straight concrete-andrubble “check dams” built across seasonally flooded gullies. Monsoon
rains fill ponds behind the structures. Only the largest structures hold water year round; most dry up six months or less after the monsoons. Their main purpose, however, is not to hold surface water but to recharge the ground water beneath. The advantages of water stored in the ground are many. It does not evaporate, but spreads out to recharge wells and provides moisture for vegetation over a wide area. In addition, it does not provide breeding grounds for mosquitoes like stagnant water collected in ponds or artificial lakes. The ground-water is also relatively protected from contamination by human and animal waste

Question 2. Compare the above system with the probable systems in hilly/mountainous areas or plains or plateau regions.

Answer. Water harvesting system in the hilly areas are quite different from those of plain areas. Like in Himachal Pradesh, parts of it had evolved local system of canal irrigation called kulhs over four hundred years ago. The water flowing in the streams was diverted into man-made channels which took this water to numerous villages down the hillside. The management of water flowing in this kulhs was done by a common agreement between all the villages. Interestingly, during the planting season, water was first used by the village farthest away from the source of the kulh, then by villages progressively higher up. These kulhs were managed by two or three people who were paid by the villagers. In addition to irrigation, water from these kulhs also percolated into the soil and fed springs at various points.

Question 3. Find out the source of water in your region/locality. Is water from this source available to all people living in that area?

Answer. The sources of water in my locality are ground water from tube wells which are managed by the municipal corporation. Sometimes. especially in summer season, when there is long power cut, tube wells which operate on electricity, stop supplying water. Then water is supplied through water tankers from other tube wells or water reservoir.

 Solved Exercises

Chapter 16. Management of Natural Resources | CBSE Class 10th Science  

Question 1. What changes would you suggest in your home in order to be environment-friendly?

Answer. By following the simple rule  of three R's i,e., Reduce, Reuse and Recycle, we can save the environment in an effective way.
Reduce means to use less. I would save electricity by switching off unnecessary lights and fans, perfer to walking and cycling than using a vehicle, turn off the engine at red lights, repair leaky taps, and would not waste food etc.
Reuse refers to use things again and again. For example, instead of throwing away used empty cans or plastic jars, they can be used for storage of groceries in kitchen.
And Recycle means collect used things like plastic, paper, glass or metal and send them for recycling.

Question 2. Can you suggest some changes in your school which would make it environment-friendly?

Answer. As discussed in the previous answer, always remembering three R's i,e., Reduce, Reuse and Recycle while using resources around, is the best way to become environment friendly.

Question 3. We saw in this chapter that there are four main stakeholders when it comes to forests and wildlife. Which among these should have the authority to decide the management of forest produce? Why do you think so?

Answer. Out of four stakeholders viz., the local people, the Forest Depatment, the industrialist, and the wildlife and nature enthusiasts, I think the best authority to decide the management of forest produce will be the local people i.e., the people who live nearby or in the forests. Because, the local people use of forest in a sustainable manner. For centuries, the local people had been using the forest but they had developed such practices that an optimum amount of produce is left for all generations to come. Besides, the traditional use of forest areas by shepherds etc. only ensure the balance in the forests ecology.
Further, management of forests by keeping te local people out only leads to damage of the forests. In fact, forest resources ought to be used in a manner that is both environmentally and develop-mentally sound, i.e.,, keeping the environment preserved, the befits of the controlled exploitation go to the local people.

Question 4. How can you as an individual contribute or make a difference to the management of (a) forests and wildlife, (b) water resources and (c) coal and petroleum?

Answer. (a) Forest and wildlife: Forests resources cannot be handled without an active participation of the local people. An example of it is of sal forests of Arabari which underwent a remarkable recovery. So, I will ensure people's active participation. I will also ensure an equitable distribution of resources in a sustainable manner so that all and not just a handful of rich and powerful people, benfit from the development of these resources.
(b) Water resources: During our day-to-day life knowingly we waste water which must be stopped. I will ensure that I would cultivate habits so that water can be saved. Further by adopting any water harvesting technique, we can also conserve water.
(c) Coal and Petroleum: These are the main source of energy today. We can save them in many ways. For example:
  1. Use of fluorescent tubes.
  2. Switching off unnecessary electric and electronic devices.
  3. Using solar devices.
  4. Prefer walking or cycling than using vehicle.
  5. Ignition of the vehicles should be turned off while waiting on red lights.
  6. Using of stairs instead of lift.
  7. Keeping the air pressure in the types right.


Question 5. What can you as an individual do to reduce your consumption of the various natural resources?

Answer. The consumption of the various natural resources can be reduced in th following ways:
  1. Saving electricity by switching off unnecessary lights and fans.
  2. Use of fluorescent tubes.
  3. Using of stairs instead of lift.
  4. Turning off the engine of the vehicle while waiting on red lights
  5. Repairing leaky taps.
  6. By not wasting food etc.


Question 6. List five things you have done over the last one week to-
  1. conserve our natural resources.
  2. increase the pressure on our natural resources.


Answer.
(a)
  1. Saved electricity by turning off unnecessary lights.
  2. Used stairs instead of lift.
  3. Preferred to walk or use bicycle instead of using vehicle.
  4. Repaired leaky taps.
  5. Used empty glass jar of pickle for storing groceries.
  6. Used empty plastic bottles for carrying drinking water.
  7. Ate cooked food when it was hot served along with family, so no reheating

(b)
  1. Wasted water while cleaning house, washing car, watering lawn and bathing.
  2. TV remained on while I was doing home work.
  3. Turned water geyser on long before taking bath.
  4. Used bulbs instead of fluorescent tubs.
  5. Wasted cooked food.


Question 7. On the basis of the issues raised in this chapter, what changes would you incorporate in your life-style in a move towards a sustainable use of our resources?

Answer. I would incorporate the judicious use of three R's i.e., reduce, reuse and recycle in my life-style in a move towards a sustainable use of our resources. I would try to lead a simple life by avoiding all luxurious things, wasteful expenditure or over consumption of various products and services

Saturday, 29 March 2014

Chapter 15. Our Environment | CBSE Class 10th Science | Solved Exercises

Intext Questions | Page 257 |Chapter 15. Our Environment | CBSE Class 10th Science

Question 1. Why are some substances biodegradable and some non-biodegradable?

Answer. Some substances can be acted upon by the micro organisms and broken down into simple substances. Such substances are called biodegradable.
Some substances are inert and cannot be acted upon by the microorganisms and do not breakdown into simple substances. Such substances are called non- biodegradable.

Question 2. Give any two ways in which biodegradable substances would affect the environment.

Answer. Biodegradable substances affect the environment in the following ways:
  1. These substances are decomposed by the action of microorganisms. This causes fowl smell.
  2. During the process of decaying of biodegradable substances, various types of gases are released which cause air pollution.


Question 3. Give any two ways in which non-biodegradable substances would affect the environment

Answer. The non-biodegradable substances affect the environment in the following ways:
  1. They persist in the environment for a long time and thus damage the environment.
  2. Such substances cause land pollution and water pollution.


Intext Questions |Page 261 |Chapter 15. Our Environment | CBSE Class 10th Science |

Question 1. What are trophic levels? Give an example of a food chain and state the different trophic levels in it.

Answer. There are various series of organisms feeding on one another. These series of organisms taking part in various biotic levels form food chain. The steps or levels of the food chain are called trophic levels.
 There are various series of organisms feeding on one another. These series of organisms taking part in various biotic levels form food chain. The steps or levels of the food chain are called trophic levels.

The autotrophs or the producers are at the first trophic level. The herbivores or the primary consumers come at the second, small carnivores or the secondary consumers at the third and larger carnivores or the tertiary consumers form the fourth trophic level 

An example of food chain: Grass-->Deer-->Lion.
Various trophics levels:
  1. The grass , which is  autotroph or the producer, comes at the first trophic level . It fix up the solar energy and make it available for deer as primary consumer.
  2. Dear as a herbivore or  primary consumers of grass comes at  the second trophic level
  3. Lion, which is Top Carnivore, comes at Fourth trophic level. It consumes dear at second trophic level ( or others at  third trophic level).


Question 2. What is the role of decomposers in the ecosystem?.

Answer. Decomposers are called natural cleaning agent. They act on biodegradable substances and break them into simple substances. In this way, decomposers create a balance in the environment and play an important role in ecosystem.

Intext Questions | Page 264 |Chapter 15. Our Environment | CBSE Class 10th Science |

Question 1. What is ozone and how does it affect any ecosystem?

Answer. Ozone is a molecule formed by three atoms of oxygen. Ozone is formed by the reaction of three molecules of oxygen is presence of ultraviolet (UV) rays.
UV
3O2------>2O3

Ozone performs an essential function. It shields the surface of the earth from ultraviolet radiation of the sun If this radiation enters in the atmosphere, it could cause various disorders. So, ozone protects the ecosystem from damaging.

Question 2. How can you help in reducing the problem of waste disposal? Give any two methods.

Answer.
  1. There are two types of wastes; biodegradable and non-biodegradable. We should consume more and more substances that generate biodegradable wastes.
  2. Biodegradable wastes so generated, should be sent to solid waste management plants where it may be used either for compost production or making fuel bricks. Non-biodegradable waste should be segregated and then be sent to factories for recycling of products.


Solved Exercises  


Question 1. Which of the following groups contain only biodegradable items?
(a) Grass, flowers and leather
(b) Grass, wood and plastic
(c) Fruit-peels, cake and lime-juice
(d) Cake, wood and grass

Answer. (c) Fruit-peels, cake and lime-juice (d) Cake, wood and grass.

Question 2. Which of the following constitute a food-chain?
(a) Grass, wheat and mango
(b) Grass, goat and human
(c) Goat, cow and elephant
(d) Grass, fish and goat

Answer. (b) Grass, goat and human.

Question 3. Which of the following are environment-friendly practices?
(a) Carrying cloth-bags to put purchases in while shopping
(b) Switching off unnecessary lights and fans
(c) Walking to school instead of getting your mother to drop you on her scooter
(d) All of the above

Answer. (d) All of the above

Question 4. What will happen if we kill all the organisms in one trophic level?

Answer. Each and every trophic level depends for its energy needs on its previous trophic level. If all organisms of any of the trophic levels in a food chain are damaged, the organisms of other trophic levels will also be destroyed because energy flow is stopped from one trophic level to other trophic level.

The length and complexity of food chains vary greatly. Each organism at some irophic iLevel, is generally eaten by two or more other kinds of organisms of other tropic level. Which in turn are eaten by several other organisms. So instead of a straight line food chain, the relationship can be shown as a series of branching lines called a food web


Question 5. Will the impact of removing all the organisms in a trophic level be different for different trophic levels? Can the organisms of any trophic level be removed without causing any damage to the ecosystem?

Answer. No, the impact of removing all the organisms in a trophic level is same for different trophic levels. The removal of organisms of any trophic level is damaging and it causes various disorder in ecosystem.

Question 6. What is biological magnification? Will the levels of this magnification be different at different levels of the ecosystem?

Answer. When any harmful chemical like DDT enters in a food chain, its concen-tration increases gradually at each trophic level. This phenomenon is called biological magnification.
The levels of this magnification will be different at different levels of the ecosystem.

Question 7. What are the problems caused by the non-biodegradable wastes that we generate?

Answer. The non-biodegradable wastes persist in the environment for a long time and causes various problems.
Non-biodegradable wastes cause:
  1. Water pollution so that water becomes unfit for drinking.
  2. They cause land pollution and due to it land loses it beauty.
  3. They cause stoppage of flow of water in drains.
  4. They also cause air pollution and make the air poisonous.
Different compunds takes different time to biodegrade in a marine environment


Question 8. If all the waste we generate is biodegradable, will this have no impact on the environment?

Answer. The biodegradable wastes do not persist for a long time in the environment. However, they also cause harmful affects but these effects are only for sometime.These wastes can be converted into useful substances and broken into simple substances by the action of microorganism. So, there will be impact of biodegradable waste but for a short time.

Question 9. Why is damage to the ozone layer a cause for concern? What steps are being taken to limit this damage?

Answer. Enlargement of ozone hole will cause more ultraviolet rays to reach on the earth's surface. This is very harmful for us, animals and microorganisms in the following ways.
  1. Ultraviolet radiation may cause skin disease, especially skin cancer.
  2. plant life will be disturbed due to retarded growth and destruction of pigments.
  3. UV rays may kill microorganism, decomposers and other useful microbes. It may lead to ecological imbalance.

Steps to prevent damage of ozone layer:
  1. Judicious use of aerosol spray propellants such as fluorocarbon and chlorofluorocarbons which cause depletion or hole in ozone layer.
  2. Limited use of supersonic plains.
  3. Control over large scale nuclear explosions.


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Things to remember..
  • The various components of an ecosystem are interdependent.
  • Each step or level of the food chain forms a trophic level.
  • The producers make the energy from sunlight available to the rest of the ecosystem.
  • The autotrophs or the producers are at the first trophic level. They fix up the solar energy and make it available for heterotrophs or the consumers.
  • The herbivores or the primary consumers come at the second, small carnivores or the secondary consumers at the third and larger carnivores or the tertiary consumers form the fourth trophic level.
  • There is a loss of energy as we go from one trophic level to the next, this limits the number of trophic levels in a food-chain.
  • There are generally a greater number of individuals at the lower trophic levels of an ecosystem, the greatest number is of the producers.
  • Human activities have an impact on the environment.
  • The use of chemicals like CFCs has endangered the ozone layer. Since the ozone layer protects against the ultraviolet radiation from the Sun, this could damage the environment.
  • The waste we generate may be biodegradable or non-biodegradable.
  • The disposal of the waste we generate is causing serious environmental problems.
  • In nature, different materials biodegrade at different rates, and a number of factors are important in the rate of degradation of organic compounds. To be able to work effectively, most microorganisms that assist the biodegradation need light, water and oxygen. Temperature is also an important factor in determining the rate of biodegradation. This is because microorganisms tend to reproduce faster in warmer conditions. The rate of degradation of many soluble organic compounds is limited by bioavailability when the compounds have a strong affinity for surfaces in the environment
  • Different compounds takes different time to biodegrade in a marine environment.

Chapter 14. Sources of Energy | CBSE Class 10th Science | Solved Exercises

Question 1. A solar water heater cannot be used to get hot water on
(a) a sunny day.
(b) a cloudy day.
(c) a hot day.
(d) a windy day.

Answer. (b) a cloudy day.

Question 2. Which of the following is not an example of a bio-mass energy source?
(a) wood
(b) gobar-gas
(c) nuclear energy
(d) coal

Answer. (c) nuclear energy

Question 3. Most of the sources of energy we use represent stored solar energy. Which of the following is not ultimately derived from the Sun’s energy?
(a) geothermal energy
(b) wind energy
(c) nuclear energy
(d) bio-mass.

Answer. (a) geothermal energy

Question 4. Compare and contrast fossil fuels and the Sun as direct sources of energy.

Answer.
Fossil fuelsSun
1.It is conventional source of energyIt is non-conventional source of energy
2.The fossil fuels are non-renewable sources of energySun is a renewable source of energy
3.The fossil fuels have limited reserves and are depleting very fast due to over useSun is a very large and long lasting source of energy
4.Fossil fuels can be used for our energy requirement anytimeThe energy from the Sun can be derived during day time only.
5.Use of Fossil fuels results in air pollution. The oxides of carbon, nitrogen and sulphur that are released on burning fossil fuels are acidic oxides. These lead to acid rain which affects our water and soil resourcesSolar energy is totally clean and Eco-friendly fuel. It can be produce without any pollution or ecological bad effects
6.Fossil fuels cost is initially low for short usage, but overall cost becomes high over a longer period The solar energy, initially cost high for small and limited usage but for longer period and large energy requirement its cost is minimum
7.Fossil fuels involves recurring expensesSolar energy requires no recurring expenses


Question 5. Compare and contrast bio-mass and hydro electricity as sources of energy.

Answer.
.BiomassHydroelectricity
1.Biomass is a renewable and conventional source of energy.Hydroelectricity is also a renewable and conventional source of energy.
2.Biomass as source of energy makes use of chemical reaction, hence exhibits a form of chemical energyHydro electricity makes use of kinetic energy of running or falling water from height
3.Application of biomass for energy requirement causes air pollutionHydro electricity is pollution free source of energy
4.Use of biomass does not cause ecological imbalance.Construction of hydle projects for hydro electricity causes ecological imbalances.
5.Biomass is relatively more economic source of energy than hydro electricity.Hydro Electricity is relatively costly source of energy.


Question 6. What are the limitations of extracting energy from—
(a) the wind? (b) waves?(c) tides?


Answer.
(a) Limitations of extracting energy from the wind -
  1. Wind energy farms can be established only at those places where wind blows for the greater part of a year
  2. The wind speed should also be higher than 15 km/h to maintain the required speed of the turbine
  3. There should be some back-up facilities (like storage cells) to take care of the energy needs during a period when there is no wind
  4. Establishment of wind energy farms requires large area of land. For a 1 MW generator, the farm needs about 2 hectares of land
  5. The initial cost of establishment of the farm is quite high
  6. the tower and blades are exposed to the vagaries of nature like rain, Sun, storm and cyclone, they need a high level of maintenance

(b) Limitations of extracting energy from the waves -
  1. Wave energy is a viable proposition only where waves are very strong
  2. Nature , pattern and occurrence of waves is not same for different sea shore locations over time.
  3. Cost of energy production is high as a wide variety of devices are required to trap wave energy for rotation of turbine and production of electricity
(c) Limitations of extracting energy from the tides -
  1. Tidal energy is harnessed by constructing a dam across a narrow opening to the sea. A turbine fixed at the opening of the dam converts tidal energy to electricity. The locations where such dams can be built are limited
  2. Cost of energy production is high as dam construction involves large capital cost
     Tidal energy is harnessed by constructing a dam across a narrow opening to the sea. A turbine fixed at the opening of the dam converts tidal energy to electricity. The locations where such dams can be built are limited     Cost of energy production is high as dam construction involves large capital cost


Question 7. On what basis would you classify energy sources as
(a) renewable and non-renewable?
(b) exhaustible and inexhaustible?
Are the options given in (a) and (b) the same?

Answer. (a) Renewable and non-renewable : Renewable energy sources are those energy sources, which can be restored back to their original form after harnessing energy for various purpose, e.g. Hydro Electricity. Non-renewable energy sources are those energy sources, which can not be restored back to their original form or simply replenished after making use of them for energy requirement, e.g. Coal, Gas, Petrol etc.
(b) Exhaustible and inexhaustible : Sources of energy, that will exhaust in near future, are called exhaustible source e.g. Gas, Petrol, Coal etc. Sources of energy, that will not end considerably over very long period of time are called inexhaustible sources, e.g. Sun, Water, Air etc.

Question 8. What are the qualities of an ideal source of energy?

Answer. The qualities of an ideal source of energy are :
  1. An ideal source of energy is less polluting and while in use have minimum contribution towards ecological imbalance such as 'the green-house effect'
  2. It is cost effective and economical to use
  3. Its procurement, processing, storage and distribution is easy and manageable
  4. It would do a large amount of work per unit volume or mass
  5. It can be employed for diverse energy need across different fields


Question 9. What are the advantages and disadvantages of using a solar cooker? Are there places where solar cookers would have limited utility?

Answer.
Advantages of using a solar cooker
  1. It is totally pollution free
  2. It is cost effective and economical to use as there is no recurring cost.
  3. It is quite user friendly and easy to handle.
  4. It provides safety against fire related accident and injuries
  5. It provides an ideal cooking environment with no loss food value
  Solar Cooker is totally pollution free . It is cost effective and economical to use as there is no recurring cost. It is quite user friendly and easy to handle. It provides safety against fire related accident and injuries     It provides an ideal cooking environment with no loss food value
Disadvantages of using a solar cooker
  1. It takes considerably long time for food cooking
  2. Solar cookers can not be used indoor, in night time or in cloudy weather
  3. During food processing, direction of solar cooker is required to be aligned with changing direction of the Sun
  4. It can not be used for all purpose cooking e.g. making chapaties , roasting , frying
  5. The availability and Intensity of Solar energy is not same for all the time at all the places.
Yes, there are places where solar cookers would have limited utility. For example, in polar region, there is no Sun shine for almost half of the year. So solar cookers would have limited utility. In hilly areas, shady places under foothills receives very less Sun shine. For others hilly areas, Sun shine may be available for shorter period of time. The intensity of Sun light is very less on Hilly slopes as they receive inclined sun rays. So in such places solar cookers would have limited utility.

Question 10. What are the environmental consequences of the increasing demand for energy? What steps would you suggest to reduce energy consumption?

Answer. The unprecedented and ever increasing scale of urban development together with rapid pace of industrialization has fueled the demand for energy many folds. This ever increasing demand of energy has resulted in adverse environmental consequences, which are as given below :
  1. To keep the pace of modern development, ever increasing demand for energy has resulted in indiscriminate usage and exploitation of energy resources, which is causing a great damage to environment and creating ecological-imbalances in the form of man made disasters such as green house effect or global warming
  2. The available reserves of energy resources are limited. To meet the increasing demand for energy, these reserves are being depleted very fast, which may lead to theirs scarcity or energy crisis in near future.
To reduce energy consumption, following steps can be suggested :
  1. We should make best use of public transport system such as Rails, Buses and should try to avoid private transport whenever and where ever possible
  2. We should adopt new life style of living with minimum waste of energy in Cooking, Home lighting, Cooling or heating
  3. The use of alternative or non-conventional sources of energy such as Solar energy, wind energy, hydro energy, Tidal energy, wave energy and Ocean Thermal Energy should be optimised to supplement the demand for energy from non-renewable source of energy.
  4. We should impose a ceiling on per capita energy consumption through limited availability or price linked with energy consumptions to discourage its misuse


Things to remember

  • Our energy requirements increase with our standard of living.
  • In order to fulfill our energy requirements, we try to improve the efficiency of energy usage and also try and exploit new sources of energy.
  • We also need to look for new sources of energy because the conventional sources of energy like fossil fuels are in danger of getting exhausted soon.
  • The energy source we select would depend on factors like the ease and cost of extracting energy from the source, the efficiency of the technology available for using that source of energy and the environmental impact of using that source.
  • Many of the sources ultimately derive their energy from the Sun.

Monday, 24 March 2014

Chapter 13. Magnetic Effects of Electric Current | Science - CBSE Class 10th | Solved Exercises

Question 1. Which of the following correctly describes the magnetic field near a long straight wire?
(a) The field consists of straight lines perpendicular to the wire.
(b) The field consists of straight lines parallel to the wire.
(c) The field consists of radial lines originating from the wire.
(d) The field consists of concentric circles centred on the wire.

Answer. (d) The field consists of concentric circles centred on the wire.

Question 2. The phenomenon of electromagnetic induction is
(a) the process of charging a body.
(b) the process of generating magnetic field due to a current passing through a coil.
(c) producing induced current in a coil due to relative motion between a magnet and the coil.
(d) the process of rotating a coil of an electric motor.

Answer. (c) producing induced current in a coil due to relative motion between a magnet and the coil.

Question 3. The device used for producing electric current is called a
(a) generator.
(b) galvanometer.
(c) ammeter.
(d) motor.

Answer. (a) generator.

Question 4. The essential difference between an AC generator and a DC generator is that
(a) AC generator has an electromagnet while a DC generator has permanent magnet.
(b) DC generator will generate a higher voltage.
(c) AC generator will generate a higher voltage.
(d) AC generator has slip rings while the DC generator has a commutator.

Answer. (d) AC generator has slip rings while the DC generator has a commutator.

Question 5. At the time of short circuit, the current in the circuit
(a) reduces substantially.
(b) does not change.
(c) increases heavily.
(d) vary continuously.

Answer. (c) increases heavily.

Question 6. State whether the following statements are true or false.
(a) An electric motor converts mechanical energy into electrical energy.
(b) An electric generator works on the principle of electromagnetic induction.
(c) The field at the centre of a long circular coil carrying current will be parallel straight lines.
(d) A wire with a green insulation is usually the live wire of an electric supply.

Answer. (a) False (b) True (c) True (d) False

Chapter 13. Magnetic Effects of Electric Current | Science - CBSE Class 10th  | Solved Exercises
Question 7. List three methods of producing magnetic fields.

Answer. Three methods of producing magnetic fields are as follows
(i) A natural magnet or bar magnet produces magnetic fields around it.
(ii) A current carrying conductor, which may be a straigt or circular, produces magnetic fields around it
(iii) Current passing through A a solenoid, generates uniform and strong magnetic fields inside the solenoid.


Question 8. How does a solenoid behave like a magnet? Can you determine the north and south poles of a current–carrying solenoid with the help of a bar magnet? Explain.

Answer. A coil of many circular turns of insulated copper wire wrapped closely in the shape of a cylinder is called a solenoid.In fact, one end of the solenoid behaves as a magnetic north pole, while the other behaves as the south pole. The field lines inside the solenoid are in the form of parallel straight lines. This indicates that the magnetic field is the same at all points inside the solenoid. That is, the field is uniform inside the solenoid.
Yes, We Can determine the north and south poles of a current–carrying solenoid with the help of a bar magnet. As we know, the magnetic field so produced by the solenoid, exerts a force on a magnet placed in the vicinity of the conductor.The magnet must also exert an equal and opposite force on the current-carrying conductor. When the Magnetic poles of solenoid and bar magnet are same, they will repell each other and when they are unlike, they will attract each other. There fore, on bringing bar magnet towards one end of solenoid, if the north pole of the bar magnet is repelled, then the end of solenoid under consideration is the south pole and vice-versa

Question 9. When is the force experienced by a current–carrying conductor placed in a magnetic field largest?

Answer. The force experienced by a current–carrying conductor placed in a magnetic field largest, when the direction of current is at right angles to the direction of the magnetic field
Explanation:We know that the force experienced by a current–carrying conductor placed in a magnetic field is given as :
F = BIL sin Θ
B = Magnetic Field
I = Current strength
L = Length of conductor
F = Force
Θ = Angle between direction of magnetic field and current-carrying conductor
So, F, the force will be maximum if Θ = 900 as sin 900 = 1 is the maximum value of sin Θ.

Question 10. Imagine that you are sitting in a chamber with your back to one wall. An electron beam, moving horizontally from back wall towards the front wall, is deflected by a strong magnetic field to your right side. What is the direction of magnetic field?

Answer. The direction of magnetic field will be at right angles to the direction of plain of moving beam and direction of force acting on it.

CBSE Class 10th Science  |Chapter 13. Magnetic Effects of Electric Current |  Solved Exercises

Question 11. Draw a labelled diagram of an electric motor. Explain its principle and working. What is the function of a split ring in an electric motor?

Answer.

Labelled diagram of an electric motor. Its principle and working

Principle : An electric motor is a rotating device that converts electrical energy to mechanical energy. In principle, an electric current flowing through a conductor produces a magnetic field. When such current-carrying conductor is placed in a magnetic field of an external magnet, depending upon the polarities of magnetic fields in interaction, it either experiences electromagnetic force of attraction or repulsion. The direction of this force, according to Fleming’s left-hand rule, is perpendicular to both direction of magnetic field and the direction of current

Working : An electric motor, as shown in Fig., consists of a rectangular coil ABCD of insulated copper wire. The coil is placed between the two poles of a magnetic field such that the arm AB and CD are perpendicular to the direction of the magnetic field. The ends of the coil are connected to the two halves P and Q of a split ring. The inner sides of these halves are insulated and attached to an axle. The external conducting edges of P and Q touch two conducting stationary brushes X and Y, respectively, as shown in the Fig.
Current in the coil ABCD enters from the source battery through conducting brush X and flows back to the battery through brush Y. Notice that the current in arm AB of the coil flows from A to B. In arm CD it flows from C to D, that is, opposite to the direction of current through arm AB.


On applying Fleming’s left hand rule for the direction of force on a current-carrying conductor in a magnetic field (see Fig.). We find that the force acting on arm AB pushes it downwards while the force acting on arm CD pushes it upwards. Thus the coil and the axle O, mounted free to turn about an axis, rotate anti-clockwise. At half rotation, Q makes contact with the brush X and P with brush Y. Therefore the current in the coil gets reversed and flows along the path DCBA.

Function of a Split ring
 A device that reverses the direction of flow of current through a circuit is called a commutator. In electric motors, the split ring acts as a commutator. The reversal of current also reverses the direction of force acting on the two arms AB and CD. Thus the arm AB of the coil that was earlier pushed down is now pushed up and the arm CD previously pushed up is now pushed down. Therefore the coil and the axle rotate half a turn more in the same direction. The reversing of the current is repeated at each half rotation, giving rise to a continuous rotation of the coil and to the axle.

Question 12. Name some devices in which electric motors are used

Answer. The name of some devices which make use of electric motors are as given below :
(i) Electric Fans & Cooler
(ii) Mixer Juicer & Grinder
(iii) Washing Machines
(iv) A.C. and Refrigerator
(v) Escalators and Lifts
(vi) Tube Wells and Water Pumps
(vii) Lathe Machine, Saw Mill, Drilling Machine etc

Question 13. A coil of insulated copper wire is connected to a galvanometer. What will happen if a bar magnet is (i) pushed into the coil, (ii) withdrawn from inside the coil, (iii) held stationary inside the coil?

Answer. When a coil of insulated copper wire is connected to a galvanometer, its needle may undergo deflection showing presence of current, only if there is an induced current in the coil.
(i) When a bar magnet is pushed into the coil, due to gradual and relative change in the strength of magnetic field, a current will be induced in the coil, which will cause the deflection in the galvanometer.
(ii) When a bar magnet is withdrawn from inside the coil, agin, due to gradual and relative change in the strength of magnetic field, a current will be induced in the coil, which will cause the deflection in the galvanometer but now in opposite direction.
(iii) When a bar magnet is held stationary inside the coil, there will be no gradual and relative change in the strength of magnetic field, hence no current will be induced in the coil. We will observe no deflection in galvanometer.

Question 14. Two circular coils A and B are placed closed to each other. If the current in the coil A is changed, will some current be induced in the coil B? Give reason.

Answer. We know, when a coil is placed in a region where the magnetic field changes with time, there is the production of induced current in the coil due to phenomenon of electromagnetic induction. If the coil is placed near to a current-carrying conductor, the magnetic field may change either due to a change in the current through the conductor or due to the relative motion between the coil and conductor. Here, when the the current in the coil A is changed, its corresponding magnetic field will also undergo change in its strength. As coil B is placed closed to coil A, an induced current will be produced in the coil B also.

Question 15. State the rule to determine the direction of a (i) magnetic field produced around a straight conductor-carrying current, (ii) force experienced by a current-carrying straight conductor placed in a magnetic field which is perpendicular to it, and (iii) current induced in a coil due to its rotation in a magnetic field.

Answer. For the given cases above, the rules to be observed are as given below :
Case 1 : The direction of a magnetic field produced around a straight conductor-carrying current is given by the right-hand thumb rule.

Right-hand Thumb rule.- Direction of a magnetic field

According to this rule, when we hold a current-carrying straight conductor in our right hand such that the thumb points towards the direction of current. Then direction of our fingers wrapped around the conductor points to direction of the field lines of the magnetic field.
Case II : The direction of a force experienced by a current-carrying straight conductor placed in a magnetic field which is perpendicular to it, is given by Fleming’s left-hand rule.

The direction of a force experienced by a current-carrying straight conductor  - Fleming’s left-hand rule.

According to this rule, stretch the thumb, forefinger and middle finger of your left hand such that they are mutually perpendicular. If the first finger points in the direction of magnetic field and the second finger in the direction of current, then the thumb will point in the direction of motion or the force acting on the conductor.

Case III : The direction of current induced in a coil due to its rotation in a magnetic field is given by Fleming’s right-hand rule


According to this rule, Stretch the thumb, forefinger and middle finger of right hand so that they are perpendicular to each other, as shown in Fig. If the forefinger indicates the direction of the magnetic field and the thumb shows the direction of motion of conductor, then the middle finger will show the direction of induced current.

CBSE Class 10th Science| Solved Exercises  |Chapter 13. Magnetic Effects of Electric Current | 
Question 16. Explain the underlying principle and working of an electric generator by drawing a labelled diagram. What is the function of brushes?

Answer. Principle : An electric generator converts mechanical energy into electrical energy. The working principle of electric generator is based on the phenomenon of electromagnetic induction. According to which, when a coil or conductor is placed in a changing magnetic field, a induced current is produced in the coil. In an electric generator, mechanical energy is used to rotate a coil or conductor in magnetic field. Due to the relative motion of the coil inside a magnetic field of magnet, the coil or conductor is subjected to continuous changing magnetic field, hence there is a production of induced current in the coil. The direction of the induced current is given by the Fleming’s right-hand rule.
Electric Generator Labelled diagram

Construction : An electric generator, as shown in Fig., consists of a rotating rectangular coil ABCD as an armature placed between the two poles of a permanent magnet. The two ends of this coil are connected to the two metallic slip rings R1 and R2, which are mounted seperately on one end of the axle of rotating coil. The inner side of these rings, are made insulated, so that these are not in contact with either the axle or with each other. The two brushes B1 and B2, which are made of soft conducting material such as carbon, are kept pressed separately on the outer surface of rings R1 and R2, respectively. Outer ends of the two brushes are connected to galvanometer through connecting wires to show the flow of current in the given external circuit. We can also connect an electric load in the external circuit.
Working : In an electric generator, the armature coil ABCD is mechanically rotated from outside through its axle, inside the magnetic field to produce electricity. The slip rings R1 and R2, which are mounted separately on the axle of armature coil, are connected to two ends of armature coil ABCD and while in rotation, these rings are also in contact with outer stationary brushes B1 and B2.
As the armature coil rotate clockwise in the arrangement shown in Fig, the arm AB moves up and the arm CD moves down sweeping across the magnetic field produced by the permanent magnet. The induced currents are set up in these arms along the directions AB and CD, according Fleming’s right-hand rule. Thus an induced current flows in the direction ABCD. As there are larger numbers of turns in the coil, the current generated in each turn adds up to give a large current through the coil. This means that the current in the external circuit flows from B2 to B1. After half a rotation, arm CD starts moving up and AB moving down. As a result, the directions of the induced currents in both the arms change, giving rise to the net induced current in the direction DCBA. The current in the external circuit now flows from B1 to B2.
Thus after every half rotation the polarity of the current in the respective arms changes. Such a current, which changes direction after equal intervals of time, is called an alternating current (abbreviated as AC). And electric generator producing an alternating current is called an AC generator.
Function of Brushes : The two fixed brushes B1 and B2, which are made of soft conducting material such as carbon, are in contact separately with the outer surface of rotating rings R1 and R2, respectively. These brushes dynamically connect the electric load in the external circuit with induced current in armature coil through its ends for output power.

Question 17. When does an electric short circuit occur?

Answer. An electric circuit consist of live wire (or positive) usually with red insulation cover and neutral wire (or negative) with black insulation. In some situation, when the wire insulation is either damaged or there is some fault in the appliance, the live wire and the neutral wire may come into direct contact. This results in a very large amount of current passing through the circuit resulting in occurrence of a short circuit.

Question 18. What is the function of an earth wire? Why is it necessary to earth metallic appliances?

Answer. Connecting the metal case of an electric appliance to a metal plate deep in the earth near the building by means of a metal wire is called earthing. It is used as a safety measure specially for those appliances which have a metallic body. The metallic body is connected to the earth wire which provides a low resistance conducting path for the current. Thus, if there is any leakage of the current to the metallic body of the appliance, the user is protected from any severe shock.