Sources of Energy
What is a good source of energy? [2010,2013]
A good source of energy has the following characteristics:
- It should be capable of delivering desired quantity of energy at a steady rate over a long period of time.
- It must be convenient to use.
- It must be easy to transport and store.
- It doesmot cause environmental pollution.
What is a good fuel?
List any four characteristics of a good fuel. 
For a fuel to be good, it should:
- have a high calorific value.
- not produce any harmful product on burning.
- cause minimum pollution of air.
- be easy to handle and store.
If you could use any source of energy for heating your food, which one would you use and why?
We would use a gas stove or microwave oven for heating food because it does not produce any pollution.
What are disadvantages of fossil fuels? 
Fossil fuels have the following disadvantages:
- They release atmospheric pollutants which
- increase the greenhouse effect
- produce acid rain
- cause health problems.
- Being a non-renewable source, they will eventually run out
Why are we looking at alternate sources – of energy?
State one reason that has necessitated to look for alternate sources of energy? 
Fossil fuels are sources of energy that were formed millions of years ago. Fossil fuels are non-renewable natural sources. This means that they cannot be replaced. Once they are gone, they are gone forever. If we continue to use these sources at present rate, we should not conserve them. Therefore, we are looking at alternate sources of energy.
How has the traditional use of wind and water energy been modified for our convenience? 
The traditional use of wind and water energy has been modified by using windmills and hydroelectric power plants respectively,
What kind of mirror—concave, convex or plane would be best suited for use in a solar cooker? Why?
A concave mirror is best for a solar cooker because it reflects and concentrates the solar radiation.
What are limitations of the energy that can be obtained from the oceans? [2010,2012]
Limitations of ocean energy are:
- High cost is needed to build.
- Can damage natural habitats.
- May restrict movement of ships.
- Maintenance is difficult.
What is geothepnal energy? [2010-2012]
The energy of the earth due to its internal heat which can be used as source of energy under some suitable conditions caused by natural action is called geothermal energy.
What are the advantages of nuclear energy?
- Nuclear energy produces lots of energy from small amounts of fuel.
- It has a little maintenance.
- It has a little atmospheric pollution, providing strict precautions are taken. .
Hydrogen has been used as a rocket fuel. Would you consider it a cleaner fuel than CNG? Why or why not?
Yes, hydrogen is a cleaner fuel than CNG.This is because hydrogen on burning produces water, while CNG produces carbon dioxide in a small quantity.
Name two energy sources that you would consider to be renewable. Give reasons for your choices.
- Biomass is a renewable source of energy because waste materials such as wood shavings, dry leaves, dry stem bagasse, sewage, cattle dung, etc. are produced continuously.
- Wind is an another renewable source of energy because it is available in abundant in our natural environment.
Give the names of two energy sources that you would consider to be exhaustible. Give reasons for your choices.
Coal and petroleum.
Reasons: These sources are formed over millions of years ago, so they are present in limited amount.
Chapter End Questions
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
(b) a cloudy day
Which of the following is not an example of a biomass energy source?
(c) Nuclear energy
(c) Nuclear energy
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
(a) Geothermal energy
Compare and contrast biomass and hydro-electricity as sources of energy.
|1. It is renewable source of energy.||1. It is also a renewable source of energy.|
|2. It is clean and does not produce smoke.||2. It is also clean source of energy.|
|3. For obtaining energy, we use chulhas and gobar gas.||3. For obtaining energy, we construct dams on rivers.|
Compare and contrast fossil fuels and the sun as direct source of energy.
Differentiate between energy obtained by burning fossil fuels and that obtained as solar energy. 
|1. These are non-renewable sources of energy.||1. It is a renewable source of energy.|
|2. These fuels cause pollution.||2. It is a clean and non-polluting source of energy.|
|3. Fossil fuels are formed by dead plants and animals which had trapped sun’s energy and get converted into chemical energy.||3. It is the most important source of energy on the earth.|
What are the limitations of extracting energy from
(a) the wind?
- Wind energy cannot be harnessed at places where wind does not blow regularly.
- The cost of construction of wind energy farms is high because they need & large area to set up.
- As air is sometimes still and the other times there are storms, so wind is not a dependable source of energy.
- The power output is of variable nature.
- The cost of manufacturing with modem available technologies is high.
- Wave energy structures can affect marine animals.
- The power output is of variable nature because of variation in tide range.
- It is difficult to construct barrage in areas of high tidal flow.
- The production of power is not very large. It is irregular.
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?
(a) Renewable sources of energy are continually replenished through a number of natural processes and will never run out. These are available free of cost and are ecofriendly. Whereas non-renewable sources of energy are those which once used up cannot be replaced over millions of years. Moreover burning of fossil fuels limit their source.
(b) Coal, petroleum, natural gas, etc. are exhaustible sources of energy as their quantity is limited and they get exhausted on their continuous usage for which eventually take long period to get renewed up.
Solar energy, wind energy, etc. are inexhaustible sources of energy. These sources of energy can be used endlessly and never get exhausted.
The options given in (a) and (b) are the same in the way of availability, but some are not available always.
What are the advantages and disadvantages of using a solar cooker? Are there places where solar cookers would have limited utility? 
Advantages of a solar cooker:
- As heating is done using solar radiations there is a saving in fuels, consumed such as coal, kerosene, LPG, etc. It also saves electricity.
- A solar cooker produces no smoke and hence causes no pollution.
- The nutritional value of the food is preserved as food gets cooked very slowly.
- There are no hazards such as fire, electric shock or bursting of gas cylinder.
Disadvantages of solar cooker:
- It cannot work in a closed room.
- It cannot work in cloudy and rainy days.
- The reflector has to be adjusted each time to the sun.
- Baking and frying take a lot of heat energy which cannot be done on the solar cooker.
Places where weather always remains cloudy would have limited utility of a solar cooker.
What are the environmental consequences of the increasing demand for energy? What steps would you suggest to reduce energy consumption?
Some consequences of the increasing demand for energy are:
- Air pollution, acid rain and health problems are caused by the burning of fossil fuels.
- Large ecosystem is destroyed by dams which are built on rivers to generate electricity.
- Living things are affected by radioactive emission of nuclear fuels which are used to generate electricity in nuclear power plant.
Steps to reduce energy consumption:
- Non-renewable sources like fossil fuels should be used judiciously.
- Renewable sources of energy should be used more.
- Devices which take less energy like a . pressure coqker should be used.