Energy

Energy: The ability to do work is called energy. It unit is Joule (J) Types of sources of energy:

1) Renewable source of energy: The source of energy which can be regenerated again and again in the nature after their use are called renewable source of energy. They never get depleted in the nature after their use Eg.hydroelectricity, wind tide, bio-gas etc.

2) Non-renewable source of energy: The sources of energy which cant be regenerated again in the nature of their use are called non-renewable source of еnergу. They get depleted in the nature after their use. Eg Fossil fuel

a) Write any two differences between renewable and non renewable sources of energy

b) What is the main source of energy on earth?

Sun is the main source of energy on earth.

c) What is the main source of energy on sun?

The main source of energy on sun is thermo-nuclear fusion reaction of Hydrogen into Helium.

d) What the surface temperature on sun?

The surface temperature is about 5700°C on sun.

e) What the core temperature on sun?

The core temperature on sun is about 15x 10⁷°C.

f) How much energy is radiated by sun?

Sun is radiating 4×10²⁶ joule energy per second.

g) How much solar energy is received on earth?

Solar energy of 1.4 KW is received per square meter on earth.

g) The sun is the ultimate source of energy on earth. Explain

The sun is the ultimate source of energy on earth because all the sources of energy here are directly or indirectly derived from solar energy. For eg, hydroelectricity is also derived from solar energy because the heat of the sun cause evaporation of water from water resources which later changes to the cloud and then rainfall and snowfall from which the river are originated. The hydroelectricity is generated from the flowing water in the river. Similarly, wind energy is also a derived form of solar energy because heat of the sun makes the different air pressure in different places so that air flows from region of high pressure to region of lower region from which wind energy is generated. Hence, the sun is the ultimate source of energy on earth.

Fossil fuel: The substances formed from fossils that con be used as a source energy is called fossil fuel. Types of fossil fuel: Coal, Mineral oil, Natural gas

Importance of fossil fuel

1. It is cheap and easily available.
2. It is easy to transport.
3. It is energy efficient
4. It has multipurpose

Q)  Fossil fuel is also called non renewable source of energy. Why?

Fossil fuel is called non-renewable source of energy because it takes millions of years to form and it goes on depleting ofter their use as it is limited in nature.

Coal: The hard black-brownish sedimentary rocks which mainly contains carbon is called coal.

Q) Coal is also called non-renewable source of energy. Why?

Coal is also called non renewable source energy because it takes millions of years to form and goes on depleting after its use as it is limited in nature.

Hydroelectricity: The electricity generated by using water is called hydroelectricity.

Importance of hydroelectricity:

1. Though establishment of hydroelectricity project is expensive in the beginning, it is very cheap in long run.
2. It is pollution free source and renewable source of energy.
3. It is easy to transmit.
4. It has multipurpose use.
5. The modern equipments run with hydroelectricity..

a)  Nepal has very high potentiality of generating hydro-electricity. Why?

Nepal has very high potentiality of generating hydro-electricity because it is very rich in water resources as it has more than 6000 fast flowing rivers and rivulets.

b) Nepal gives more priority in generation of hydroelectricity. Why?

Nepal gives more priority in generation of hydroelectricity because It is renewable source of energy and Nepal has more than 6000 fast flowing rivers and rivulets.

c) What is capacity of Nepal to generate hydroelectricity?

83,000 MW

Alternative sources of energy: The source of energy that can be used instead of fossil fuel are called alternative sources of energy. E.g, tidal energy, geothermal energy, biogas etc

Nuclear energy: The energy which is released due to nuclear reactions called nuclear energy.

Nuclear fuel: The chemical substance which is used to release nuclear energy is called nuclear fuel. Eg, Uranium, Plutonium

Write mass-energy relatian.

Law of conservation of energy: “Energy neither can be created nor destroyed; it only can be changed into one form of energy to the other form.”

The mass energy relation is,

E= MC²  Where,

E = Energy released

M = lost mass

C = Speed of light ( 3×10⁸ m/s)

Types of nuclear reaction

There are 2 types of nuclear reaction. They areL Nuclear fusion reaction and Nuclear fission reaction

a) Nuclear fusion reaction: The nuclear reaction in which nucleus of lighter atoms combine to form nucleus of heavier atom is called nuclear fusion reaction. Eg,

Hydrogen ———> Helium + Energy (Under high temperature and high pressure)

b) Nuclear fission reaction: The nuclear reaction in which nucleus of an atom breaks down to form nucleus of lighter atoms is called nuclear fission reaction. Eg,

Uranium (235) ————> Krypton + Barium + Energy (Neutron bombard)

Q) Though nuclear energy is non-renewable source of energy, it is alternative source of energy. Why?

Though nuclear energy is non renewable source of energy, it is alternative source of energy because very less amount of nuclear fuel also con produce very large amount of energy for long time.

Q) Write any 3 differences between nuclear fusion and fission reaction.

Bio-fuel: The excretories of animals and plants residue which are as source of energy is called bio-fuel.

Bio-mass: The dry mass of excretories of animals and plants reside which are used as bio-fuel is called bio-moss.

Bio-gas: The gas obtained by decomposing animals excretories and kitchen leftovers is called bio-gas.

Advantages of bio-gas:

1. It is clean source of energy as it doesn’t produce smoke.
2. It is cheap source of energy.
3. It is renewable source of energy.
4. Better quality manure is produced.

Q) Nepal government gives subsidy in the establishment of bio-gas plant. Why?

Nepal government gives subsidy to establishment of bio-gas plant because Nepal is agricultural country so that its raw materials are easily available and it is also the renewable source of energy.

Tidal energy: The energy obtained from tidal water of ocean is called tidal energy.

Q) Tidal energy is not the alternative source of energy in Nepal. why?

Tidal energy is not the alternative source of energy in Nepal because there is no sea/ocean in Nepal as it is landlocked country.

Q) How is tidal energy obtained? Explain.

The high dam constructed in coastal area in which water is collected during high tides. This water is allowed to flow in ocean which rotates turbine. The rotating turbine rotates armature of generator and electricity is produced. In this way, tidal energy is obtained.

Q) How is nuclear energy obtained?

Nuclear fission reaction to conduced in nuclear power plant which release enormous amount of heat. This heat boils the water. The steam of boiling water runs steam engine which now runs generator and thousands of megawatt electricity ie generated. In this way, nuclear energy is obtained.

Wind energy: The energy obtained from wind is called wind energy.

Q) Where due the wind blow?

Wind blows due to difference in air pressure at different places due to heat of the sun.

Q) How is wind energy obtained?

Some wind mills are kept in the place where continuous wind blow occurs. The blowing wind rotates the mills which relates the turbine. The rotating turbine rotate armature of generator and electricity is generated. In this way, wind energy is obtained.

Geothermal energy: The heat energy present beneath the earth surface is called geothermal energy.

Q) What is the difference in temperature beneath the earth surface?

The temperature goes an increasing by 30C per kilometer in volcanic region and by 80C per kilometer in volcanic region.

Q) How is geothermal energy obtained?

Two deep wells are made in the region where the surface of the earth is hotter and they are connected at bottom. The water is passed into a well so that it vaporises instantly and vapour comes out of another well. The turbine kept in the way of vapour is rotated which rotates generator and electricity is generated. In this way, geothermal energy is obtained.

Solar energy: The energy obtained from sunlight is called solar energy. It is used to heat water and get electricity.

Q) Scientists are busy in designing the solar equipment. Why?

Scientists are busy in designing the solar equipment because it is the best alternative source of energy and it is environmental friendly of energy.

Energy crisis: The scarcity of energy sources due to its over exploitation is called energy crisis.

Causes of energy crisis:

1. Dependence on non-renewable source of energy.
2. Excessive use of non-renewable sources of energy.
3. Limited source of energy on earth.
4. Unwise use of energy sources.
5. Population growth.
6. Urbanization and scientific development

Prevention measures of energy crisis:

1. Use of renewable sources of energy.
2. Development of alternative sources of energy.
3. Wise use of energy source.
4. Use of energy efficient devices.
5. Population control.

Present status of energy:

1. How much energy demand of the world is fulfilled from mineral oil? 35%
2. How much energy demand of the world’s fulfilled from coal? 27%
3. What is the increment of the demand of energy source in world? 2.3% per year
4. How much energy demand of the world is fulfilled from non-renewable source/fossil fuel? 75 %

Solved exercise:

A) Very short answer questions:

a) What is fuel?

A substance which produces energy on combustion is called fuel

b) What is the major component gas in bio-gas?

The major component gas in biogas is Methane gas (CH4).

c) What is the use of leftover slurry in bio-gas plant?

Leftover slurry in bio-gas plant is used as compost manure.

d) What are the major gases found in the sun? Mention their percent of abundance

Major gases found in the sun are: Hydrogen-70% and Helium-28%

e) What type of coal is considered as the best in terms of purity?

Anthracite is considered as the best in terms of purity.

f) What fraction of petroleum after extraction can’t be used as source of energy?

Asphalt can’t be used as source of energy.

g) What is the net hydroelectric potential of our country!

Hydroelectric potential of our country is 83,000 MW

h) Mention the places where the wind con be utilized in Nepal.

The places where the wind can be utilized in Nepal are Mustang, Dolpa, Mugu etc.

B) Short answer questions.

a) Why are coal and mineral oil called Fossil fuel?

Coal and mineral oil are called fossil fuel because they are formed from remains of plants and animals that lived many years ago in the interior of the earth due to geological cause.

b) Why are bio-fuel and hydropower energy considered more useful in our country?

Bio-fuel and hydro power energy are considered more useful in our country because both of them can be used as source of energy as Nepal is agricultural country. So that bio-fuel can easily be obtained and Nepal is rich in water resource as it has more than 6000 fast flowing rivers and rivulets.

c) Can solar energy be the best alternative source of energy in our country? Justify it.

Yes, solar energy can be the best alternative source of energy in our country because Nepal is facing towards the south direction so thot sufficient solar energy con be received.

d) Write difference between solar and bio-mass energy.

e) Write difference between nuclear fuel and bio-fuel energy.

f) Government should encourage the people to use solar energy in Nepal.

Government should encourage the people to use solar energy in Nepal because it is renewable clean and best alternative source of energy in the context of Nepal.

g) Use of geothermal energy isn’t possible to generate electricity Nepal.

Use of geothermal energy is not possible to generate electricity in Nepal because geothermal energy can be easily obtained in volcanic regions but there aren’t any volcanic regions in Nepal.

h) Human beings are going to face energy crisis in near future.

Human beings are going to face energy crisis in near future because we are dependent on non-renewable source of which is limited in nature.

i) In absence of energy a person is just like an inanimate matter. Justify it

The energy is required to do every activities by a person like walking, talking etc. It is also required for every important life process like respiration, heart beat etc which keeps the person alive. Therefore, in absence of energy a person is just like inanimate matter.

j) What conditions are required for the sun to favour nuclear fusion?

Conditions required for the sun to favour nuclear fusion are: sufficient amount of hydrogen and very high pressure and temperature.

k) List any 4 uses of hydropower energy.

Four uses of hydropower energy are:

1. Used to produce heat and light.
2. Used to run industries.
3. Used to run vehicles.
4. Used to run modern equipment and devices like TV, mobile, computer etc.