Energy:
- Energy is the capacity to do work.
- The object which releases energy is called the source of energy.
- The primary source of energy is divided into two parts
- Non renewable source of energy: The source of energy which cannot be reproduced in short period of time is called non renewable source of energy. Example: Coal, Oil, natural gases, petrol, diesel, kerosene etc
- Renewable source of energy: The source of energy which can be reproduced easily in short time is called renewable source of energy. Example: Solar energy, wind energy, Bio mass, sun etc
SUN : main source of energy
All the sources of energy have stored solar energy. So, the Sun is called the major source of energy.
Physical data of the sun
Mass : 
Kg. It is about 
times that of the earth.
Kg. It is about times that of the earth.
Diameter : 
kilometre. It is about 109 times that of the earth.
kilometre. It is about 109 times that of the earth.
Density : 
Temperature : about 
Pressure : In the core of the sun there are tremendously high pressure due to the mass outside the core
Conditions for chemical reaction on the Sun’s surface:
- There is sufficient hydrogen and Helium gas on the Sun surface.
- There is spontaneous temperature and pressure on the Sun surface.
The sun is the ultimate source of energy because all the other energy that we use on earth are derived from sun. some of the examples are:
- Solar heat changes sea water into vapour and rises up in the atmosphere. Clouds are formed from vapour. When the cloud is condensed due to cooling water drop down in the form of rain, snow, hail stone, etc and river is formed in the mountain. Such river flowing down a mountain has enormous energy, from which hydroelectricity is produced. Hence, hydroelectricity is the product of solar energy.
- In the process of photosynthesis a green plant transforms solar energy into chemical energy and is stored primarily in the molecule of glucose. When plant products like wood, straw etc burn the chemical energy is released in the form of heat. So, the energy found in the food we eat and other biomass is the energy of the sun.
- Fossil fuels like coal, natural gas, mineral oils are produced from plant remains millions of years ago. So energy produced from burning fossil fuels is derived from solar energy.
- Because of solar heat air gets heated in certain parts of atmosphere where the sun is direct. The hot air rises up as it is lighter than cold air and the pressure becomes low there. Air from the surrounding flows towards the area with low pressure of air and wind is produced. So, wind energy is also the product of solar heat.
- All the living being including human beings get heat from the sun to keep their bodies warm and alive.
Nuclear reaction: When a nucleus splits up into two or more than two nuclei or when two or more than two nuclei fuse together to form a single nucleus then it is called nuclear reaction. Nuclear reaction occurs on the surface of the Sun.
Nuclear fusion reaction: When two or more than two nuclei fuse together to form a single nucleus then it is called nuclear fusion reaction. example Hydrogen nuclei fuse together to form Helium nucleus.
Nuclear fission reaction:When a bigger nucleus splits up into two or more than two nuclei then it is called nuclear fission reaction. Example: Uranium nucleus splits up to form thorium and Helium nuclei.
Fossil fuel : The source of energy which is obtained from the remains of the living things is called fossil fuel. Example: Coal, mineral oil etc
Coal: A black rock found in the mines and mainly composed of carbon is called coal. It is called fossil fuel because it is made from fossilization of plant buried under ground.
Mineral Oil : The oil extracted from mines is called mineral oil. Petrol, diesel, kerosene, mobil, paraffin, etc are the examples of mineral oil.
Advantages of coal, fossil fuel and Mineral oil
- It is comparatively cheaper and more abundant.
- It is a versatile fuel that can be used to propel vehicles.
- It is also used to produce electricity in thermal power plant.
- It is easy to store fossil fuel
- It is multipurpose fuel.
HYDROELECTRICITY
Water collected in the reservoir at great height possesses potential energy. When it flows down its potential energy changes into kinetic energy. This kinetic energy drives turbine and ultimately runs generator to produce electricity. In this way the electricity produced by running water is called hydroelectricity.
ADVANTAGES OF HYDROELECTRICITY
- It is a renewable source of energy.
- It is pollution free.
- Although production cost is high the running cost is low. So it becomes cheap source in the long run
- Transmission of electricity is cheaper and easier.
- It is easy to use.
- It operates the modern devices.
- It is cheaper, easy and non exhaustible.
ENERGY CRISIS:
The critical situation produced by the shortage of fossil fuel due to exhaustion of natural reserve is called energy crisis.
The reasons behind energy crisis are following:
a. Rapid use of fossil fuel due to increasing population and increasing trend of spending oil to live comfortable life.
b. fossil fuel is non-renewable and it takes millions of years to produce it in nature.
c. limited reserve of fossil fuel in nature will be exhausted one day in future.
Ways to solve energy crisis
1. The fuel should be used wisely and economically.
2. The existing fuel should be conserved.
3. The alternative source of energy should be developed.
4. Latest and modern technologies should be used to minimize the consumption of fossil fuel in the vehicles
Alternative energy sources
Energy sources, which can be used to preserve the non-renewable energy sources for the future, are called alternative energy sources. All the perpetual and renewable energy sources come in this category. Nuclear fission is non-renewable energy source but it is used by some countries only. Thus it is also considered as alternative energy source.
1. What are the disadvantages of fossil fuels?
- They releases toxic gases like, CO (carbon monoxide),
(Sulphur dioxide) which can change the global climate.
- They also comes in contact with water and forms acid which cause environmental hazards.
2. Write 1 advantage and disadvantage of nuclear energy?
Advantage: It is used to make nuclear weapons and a nuclear fuel during nuclear fission.Disadvantage: Harmful nuclear waste is produced during nuclear reaction which destroy aquatic life.
3. What causes nuclear fusion reaction in the sun?
Presence of plenty of hydrogen, sufficient temperature and high pressure on the inner core of the sun cause nuclear fusion reaction in the sun.
4. State mass energy relation.
“When a part of mass is lost during nuclear reaction, the lost mass gets converted into energy” This relation is known as mass — energy relation.
5. Geothermal energy can be used as alternative source of energy. Why?
Geothermal energy can be used as alternative source of energy because this energy is originated from the certain geological part of the earth’s crust.
6. Nepal has high potentiality for producing hydroelectricity however difficult to produce it. Why?
Nepal has high potentiality for producing hydroelectricity however difficult to produce it because of lack of manpower and money.
7. The development of hydro-power helps to reduce energy crisis further.
The development of hydropower helps to reduce energy crisis further because of the following reasons:* It is a renewable source of energy which is never depleted.* It does not cause any environmental pollution.
8. Renewable source can be an alternative to non-renewable sources.
If non renewable sources of energy are exhausted, they can not be brought back to their original state and can cause energy crisis but not by renewable source of energy so renewable source of energy can be an alternative to non-renewable sources.
9. Energy of fossil is also derived from the solar energy.
Energy of fossil is also derived from the solar energy because the fossil fuel is formed by the decomposition of the dead bodies of plants and animals occurs which is caused due to solar energy.
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