What is a good source of energy?
A good source of energy is one that
1. does a large amount of work per unit volume or mass
2. can be easily accessible
3. is easy to store and transport, and
4. is economical.
What is a good fuel ?
Write any three characteristics of a good fuel.
A good fuel is one which has the following properties :
1. It should be fairly cheap.
2. It should be easily available.
3. Its ignition temperature should be well above normal temperature.
4. It should be conveniently handled and transported.
5. It should not produce any poisonous material during burning.
6. Its combustion rate should be steady and controllable.
7. It should not leave any residue or ash after burning.
8. A good fuel should have high calorific value so that higher amount of heat may be obtained by burning a little fuel.
If you could use any source of energy for heating your food, which one should you use and why ?
I would prefer to use cooking gas like LPG. It fulfils many of the criteria of a good fuel like its ignition temperature, good calorific value and non-polluting characteristics.
What are the disadvantages of fossil fuels ?
(i) The burning of fossil fuels produces large amount of carbon dioxide that causes increased greenhouse effect.
(ii) The burning of fossil fuels (such as coal) produces smoke which pollutes the air.
(iii) The burning of fossil fuels produces acidic gases such as sulphur dioxide and nitrogen oxide. These acidic gases cause acid rain that affects our water and soil resources.
(iv) Fossil fuels cannot be replenished in short time because it takes millions of years to form them.
Why are we looking at alternate sources of energy ?
We are looking at alternate sources of energy because of the following reasons.
The fossil fuels and nuclear fuels on the earth are limited which may not last for long.
The undesirable effects of pollution, both from the burning of fossil fuels and from the radioactive nuclear wastes of nuclear power plants are creating threat to our environment.
How has the traditional use of wind and water energy been modified for convenience ?
(i) Wind mill farms are constructed to produce electricity.
(ii) 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.
What kind of mirror-concave, convex or plane – would be the best suited for use in a solar cooker ? Why ?
A concave mirror would be best suited in a solar cooker because 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 the food.
What are the limitations of the energy that can be obtained from the oceans?
The energy from the oceans can be obtained mainly in three forms. These are
(i) tidal energy
(ii) wave energy and
(iii) ocean thermal energy
Limitations of Tidal Energy :
(i) There are very few sites around the world which are suitable for building tidal dams.
(ii) 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 : NCERT Solutions for Class 10 Science Chapter 14 Sources of EnergyTo convert ocean thermal energy into electricity, a temperature difference of 20°C (or more) between the surface water of ocean and deeper water is needed for operating OTEC power plants. This involves high cost.
What is geothermal energy ?
Energy stored as heat in certain regions of the earth (called 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 utilised to generate electricity using pipes and turbines. Sometimes hot water from the hot spot finds outlet at the surface. Such outlets are called hot springs.
What are the advantages of nuclear energy ?
The advantages of nuclear energy are that :
1. It produces a large amount of useful energy from a very small amount of a nuclear fuel (like uranium-235).
2. Once the nuclear fuel (like uranium-235) is loaded into the reactor, the nuclear power plant can go on producing electricity for two to three years at a stretch. There is no need for putting in nuclear fuel again and again.
3. It does not produce gases like carbon dioxide which contributes to greenhouse effect or sulphur dioxide which causes acid rain.
Can any source of energy be pollution free ? Why or why not ?
No source of energy can be pollution free because even if it is clean, its assembly could have caused some environmental damage.
Hydrogen has been used as rocket fuel. Would you consider it a cleaner fuel than CNG ? Why or why not ?
Hydrogen is cleaner fuel than 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 gas and water. The carbon dioxide can produce greenhouse effect in the atmosphere and lead to the excessive heating of the environment in long run.
Name two energy sources that you would consider to be renewable. Give reasons for your choices.
(i) Energy derived from biomass is a renewable source of energy because waste products are continuously produced. Plants and trees are also grown at reasonable intervals.
(ii) The energy derived from flowing water, wind, sun and ocean are renewable sources because these sources can be harnessed into energy so long as the present solar system exists.
Give the names of two energy sources that you would consider to be exhaustible. Give reasons for your choices.
Fossil fuels like coal and petroleum are exhaustible sources of energy. The estimated reserves of these fuels are said to last us for about another 200 years, while it takes millions of years for these to be formed.
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 ?
(b) Gobar gas
(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
(c) Nuclear energy
(a) Geothermal energy.
Compare and contrast fossil fuels and the sun as direct sources of energy Ans
|(i) Non-renewable source of energy.||(i) Renewable source of energy.|
|(ii) Cause a lot of air pollution.||(ii) Pollution-free, doesn’t cause any pollution.|
|(iii) They will exhaust in future.||(iii) It is a non-exhaustible source.|
|(iv) Energy can be tapped throughout the year.||(iv) Energy cannot be tapped during night and cloudy and rainy days.|
Compare and contrast biomass and hydro-electricity as sources of energy. Ans.
|(i) Renewable source of energy.||(i) Renewable source of energy.|
|(ii) Biomass plants can be installed at any place to produce biomass as energy source.||(ii) Plants can be installed only at the places where dams can be constructed.|
|(iii) To collect waste materials is a tough and costly process.||(iii) Once the plants start to work, it is not difficult to collect water.|