NCERT Class 10 Science Chapter 14 - Sources of Energy

Chapter 14 Sources of Energy

Intext Question and Answers
Question 1: What is a good source of energy?
Answer: A good source of energy would be the one:
• which would do a large amount of work per unit volume or mass
• which is easily accessible
• which is easy to store and transport
• which is economical

Question 2: What is a good fuel?
Answer: A good fuel would be the one that produces large amount of a heat on burning, produces less smoke and is easily available.

Question 3: If you could use any source of energy for heating your food, which one would you use and why?
Answer: I would prefer using LPG for heating food or for cooking purpose as it fulfils many characteristics of a good fuel like ignition temperature, good calorific value etc.

Question 4: What are the disadvantages of fossil fuels?
Answer: Disadvantages of fossil fuels are:
• Burning fossil fuels produces a large amount of smoke which pollute the air.
• The oxides of carbon, nitrogen, and sulphur, that are released by burning of fossil fuels lead to acid rain. This acid rain affects our water and soil resources.
• The fossil fuels, once used up completely, takes millions of years to replenish or regenerate.

Question 5: Why are we looking at alternate source of energy?
Answer: We are looking at alternate sources of energy as the fossil fuels and nuclear fuel (nuclear energy) which we are using at present are limited and will not sustain for a long time. Second reason for looking at alternate source of energy is because of the pollution that both, fossil fuels and nuclear fuels, produce on burning.

Question 6: How has the traditional use of wind and water energy been modified for our convenience?
Answer: Wind mill farms are been constructed to produce energy in areas where wind's velocity is more than 15 km/h.
The traditional use of energy of flowing water has been modified by establishing hydro-power plants. At hydro-power plants, the energy of falling water or flowing water is tapped by using a water turbine and then made to drive generators.

Question 7: What kind of mirror - concave, convex or plain would be best suited for use in a solar cooker? Why?
Answer: A concave mirror would be best suited in a solar cooker as it focuses the sunlight in a very small area of the solar cooker and a high temperature is produced in it, which is sufficient to cook food.

Question 8: What are the limitations of the energy that can be obtained from the oceans?
Answer: The energy obtained from ocean is of three of forms:
• Tidal energy
• Wave energy
• Ocean thermal energy

→ Limitation of tidal energy: There are very few sites around the world which are suitable for building tidal dams. The rise and fall of sea-water during high and low tides is not enough to generate electricity on a large scale.
→ Limitations of wave energy: The movement of ocean waves is associated with kinetic energy. Such sites in the world are limited where the waves strike the shore lines with sufficient power.
→ Limitations of ocean thermal energy: To convert ocean thermal energy into electricity, a difference of 20°C [temperature] or more between the surface water of ocean and deeper water is needed for operating OTEC [ocean-thermal-energy conversion] plants. This involves high cost.

Question 9: What is geothermal energy?
Answer: Energy stored as heat in certain areas/regions of the Earth [called as hot spots] is called geothermal energy. Hot spots are the locations below Earth's crust where upward moving magma gets collected due to geological changes. When underground water comes in contact with the hot spots, steam is generated. This steam is utilized to generate electricity using pipes and turbines. Sometimes hot water from the hot spots find outlet at the surface. Such outlets are called hot springs.

Question 10: What are the advantages of nuclear energy?
Answer: Advantages of nuclear energy are:
• It produces a large amount of energy from a small amount of a nuclear fuel [like uranium - 235].
• Once the nuclear fuel [like uranium - 235] is loaded into the reactor, the nuclear power plant can go on producing electricity for 2 to 3 years at a stretch. There is no need for putting nuclear fuel again and again.
• It doesn't produce gases like CO₂, which contributes to greenhouse effect.

Question 11: Can any source of energy be pollution-free? Why are why not?
Answer: No, any source of energy can't be pollution-free. Though the solar energy, which seems to be pollution-free, does pollute the environment when making them indirectly. Thus any source of energy which may be pollution free can cause harm to environment because of its assembly.

Question 12: Hydrogen has been used as a rocket fuel? Would it a you consider cleaner fuel than CNG? Why or why not?
Answer: Hydrogen is cleaner fuel compared to CNG. This is because the burning of hydrogen produces only water, which is totally harmless. On the other hand, burning of CNG produces carbon-dioxide and water. The carbon dioxide can produce greenhouse effect in the atmosphere and lead to excessive heating of the environment in a long run.

Question 13: Name 2 energy resources that you would consider to be renewable. Give reason for your choice.
Answer:
• The energy which is produced from biomass is a renewable source of energy as the waste products are continuously produced.
• The energy produced from wind, flowing water, ocean, sun are renewable source of energy as these sources can be harnessed into energy as long as the present solar system exists.

Question 14: Give the names of 2 energy sources that you would consider to be exhaustible. Give reason for your choice.
Answer:
• Fossil fuels like coal and petroleum are exhaustible source of energy. They are limited in nature and it is said that these will last us for another 200 years. Once used up, it takes millions of years to form again.




Exercise Question and Answers
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: a) cloudy day

Question 2: Which of the following is not an example of a biomass energy source?
a) Wood
b) Gobar-gas
c) Nuclear energy
d) Coal
Answer: c) Nuclear energy

Question 3: Most 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: c) Nuclear energy

Question 4: Compare and contrast between fossil fuels and the Sun as direct source of energy.
Answer:

Fossil fuels	Sun
Non-renewable source of energy	Renewable source of energy
Causes a lot of air pollution when used (burnt)	Doesn’t cause pollution
It will exhaust in future	It will not exhaust in future
Energy can be trapped throughout the year	Energy can’t be trapped during nights, cloudy or rainy days.

Question 5: Compare and contrast bio-mass and hydro electricity as source of energy.
Answer:

Bio-mass	Hydro electricity
Renewable in nature	Renewable in nature
Bio mass plants can be installed at any place	Plants of hydro electricity can be installed in those areas where dames can be constructed
Burning biomass causes pollution	Hydro electricity doesn’t cause any pollution

Question 6: What are the limitations of extracting energy from
a) wind?
b) waves?
c) tides?
Answer:
→ Limitations of wind energy:
• Wind energy farms can’t be setup everywhere. They can be setup in areas where wind blows at velocity of 15 km/h.
• The wind required to generate electricity should be strong and steady to maintain.
• The wind energy farms require a large area of land to setup. The setup of wind energy farms is expensive.

→ Limitations of wave energy:
• The harnessing of sea-wave energy would be a viable proposition only at those places where sea waves are very strong. This has constraints of time & location.

→  Limitations tidal energy:
• There are very few sites around the world which are suitable for building tidal dams. The rise and fall of sea-water during high and low tides is not enough to generate electricity on a large scale.

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 source of energy: The sources of energy which are inexhaustible in nature and are being produced continuously in nature. Examples of renewable source of energy are energy derived from wind, flowing water, tides, ocean waves etc.

→ Non-renewable sources of energy: These sources of energy are limited in nature. Once consumed, it takes millions of years to replenish or regenerate again. Examples of non-renewable sources of energy are fossil fuels etc.

b)
→ Exhaustible sources of energy are the non-renewable sources energy.
→ Inexhaustible sources of energy are renewable sources of energy.

Yes, the options given in a) & b) are same.

Question 8: What are the qualities of an ideal source of energy?
Answer: The qualities of an ideal source of energy are:
• It must give an adequate amount net of energy.
• It must be convenient to use so as to produce energy at steady rate.
• It must be easy to store and transport.

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 solar cooker:
• The use of solar cooker for cooking food saves non-renewable resources like coal, kerosene etc.
• The use of solar cooker don't produce any smoke hence it doesn't pollute the air.

→ Disadvantages of using solar cooker:
• The solar cooker can't be used during nights or cloudy days or rainy days due to the unavailability of sunlight.
• The Solar cooker needs to change its position to keep it facing towards sun.

Yes there are some areas, where there is rainfall most of the time, where the solar cooker has 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: Some of the environmental consequences of the increasing demand for energy are:
• The incomplete combustion of fossil fuels are causing acid rain, thereby damaging crops, soil and aquatic life.
• The burning of fossil fuels is increasing the amount of greenhouse gases like carbon dioxide in the atmosphere.
• Fire-wood, which is obtained by cutting trees, is causing soil erosion and destroying wildlife there.
• The construction of hydro-power plant is disrupting the ecological balance.
• Nuclear power plants are increasing radioactivity in the environment.

Some steps can be that taken to reduce energy consumption:
• Switching off lights, fans and other electrical appliances when not needed.
• Bicycles should be used for short distances instead using a vehicle to save fuels like petrol.
• Use energy efficient electrical appliances to save energy. This can be done by using CFL (compact fluorescent lamps) and tube lights in place of conventional filament-type electric bulbs.