Saturday, 29 March 2014

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

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