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  1. The different sources from which we can obtain various types of energy are meant by sources of energy. The 2 examples are:

    1. Sun --> Perpetual source
    2. Fossil fuel --> Non-renewable source

  2. The primary sources of energy are the sources of energy that are used in the same form as they are available in nature.

  3. The type of energy sources that get depleted and cannot be replaced quickly when exhausted are called non-renewable sources of energy. Any 2 examples are:

    1. Fossil fuel
    2. Natural gas

  4. The energy sources that are continuously produced in nature and are inexhaustible are called renewable sources of energy. Some examples are:

    1. Solar energy
    2. Tidal energy

  5. As we know that the sun provides both heat and light energy for all living beings. It is the main source of energy as it supplies energy for all organisms directly or indirectly. It is the storehouse of energy. It also supports the existence of other sources of energy like fossils, solar energy, hydroelectricity, bio-fuel, and so on. So, we can say that all the energy sources are the outcome of solar energy. So, the sun is the main source of energy.

  6. Any three conditions required for the thermonuclear fusion reaction in the sun are:

    1. In the sun, there is a sufficient amount of hydrogen gas.
    2. There is a very high temperature in the sun which is essential for the formation of free protons.
    3. There is necessary pressure for the combination of free protons.

  7. The fuel formed from the fossils of plants and animals buried under the earth's crust for a long time is called fossil fuel. Any two examples are:

    1. Coal
    2. Petroleum products

  8. The liquid formed of fossil fuels such as petrol, diesel, and so on is called mineral oil. Any three advantages are:

    1. It is cheaper for long-term production.
    2. It can be easily transported.
    3. It can be used to generate electricity.

  9. Any two reasons for the statement 'hydropower is better than fossil fuel.' are:

    1. Hydropower is a renewable source but fossil fuel is non-renewable.
    2. Hydropower is eco-friendly but fossil fuel pollutes the environment.

  10. Any three advantages of hydropower are:

    1. It is a renewable source of energy.
    2. It is eco-friendly.
    3. It is cheaper in the long-term.

  11. The source of energy that can be used to reduce the negative impact of non-renewable sources of energy replacing these sources is called an alternative source of energy. Its examples are:

    1. Biofuel
    2. Nuclear energy

  12. We all know, Nepal is an agricultural country. Natural wastes, sewage, etc. can be used to generate biofuel. The most practiced profession animal husbandry is also the source of different materials like decayed grasses, dung, etc which again can be used to get biofuel. On the other hand, a lot of dense forests are found in Nepal from where a high amount of biofuel can be taken. So, in the context of Nepal, biogas energy is the best source of alternative energy.

  13. The heat energy obtained from the hot rocks this is present inside the earth is called geothermal energy.

    In the place where earthquakes and volcanoes are active, the temperature increases highly in comparison to normal. The hot underground water can be brought to the surface, fill the hole, and covered by earth. Two holes are made in the upper surface. In one of them, cold water goes inside, and in another hot vapor comes out.

    This hot water vapor is used to run the steam engine rotating turbine to generate electricity.

  14. Scientists are busy making equipment based on solar energy because solar energy is taken as the most important and effective alternative source of energy as it is available in every part of the earth and doesn't have any negative effects on the environment. The light energy from the sun is converted into electrical energy with the help of photoelectric cells. The converted electric energy can be used again to get heat, light, etc. without having any deterioration to the environment.

    So, it is the best alternative source of energy pus the energy crisis further.

  15. The acute scarcity of energy sources due to overuse or exploitation by the growing population is called an energy crisis. Any 3 ways to solve it are:

    1. Adaption of alternative energy sources.
    2. Banning the use of non-renewable sources and encouraging the use of renewable sources.
    3. Using existing sources wisely and economically.

  16. The meaning of E = mc2 is when a body is moving at the speed of light, the energy produced would be equal to the product of mass that the body loses and the speed of light.

    Here,    E = Energy produced,
                 m = mass defect, and
                 c = velocity (speed) of light.

    The scientist who profounded the equation was Albert Einstein.

  17. The power generated by rotating turbines using water is called hydropower. It is the main source of energy which is a pollution-free and renewable source of energy. Energy trapped in the flowing river is used to generate power on large scale in power stations which a cheaper for the long term & widely cued in electric devices. But petroleum products are temporary. They are only for a short period of time. These products are formed from the dead remains of plants and animals that include mineral oil, coal, and natural. These resources are limited in nature. Hence, the use of hydropower should be increased rather than that of petroleum products to get energy.

  18. We all know, coal and petrol are obtained from the earth's crust that is deposited under the earth's crust from millions of years ago. These resources are limited in nature and get depleted after a single-use. It cannot be produced time and often. So, it is called a non-renewable energy source.

  19. We all know, biofuel is the organic source of energy that can be obtained from biomass, wood, hay, straw, etc. It is more eco-friendly than other sources. It also can be produced continuously and effectively even in rural areas. So, it is called a renewable energy source.

  20. We all know, fossil fuel formed from the fossils of the plants and animals that are buried under the earth's crust. It is cheaper as it is found in a huge amount. It is easier to transport this fuel It is used for various purposes like to run automobiles, factories, and even to generate electricity. So, fossil fuel is used more than other fuels in the world.

  21. We all know the sun is the main source of energy. It is an extremely large mass of hot gasses. It provides energy for all living beings on the earth directly or indirectly. It is the storehouse of energy. It produces energy called solar energy. Hence, the sun is the ultimate some of energy.

  22. a. Renewable and son sewable source of energy.

    The energy sources which can be obtained continiously are called renewable sources.The energy sources which can't be obtained continuously are called non-renewable sources.
    It is formed in a short period of time.It takes a long time to be formed.
    They never get exhausted from nature.They get exhausted from nature.

    b. Nuclear fission and nuclear fusion.

    Nuclear fissionNuclear fusion
    It is the process of splitting a single nucleus into many nuclei.It is the process of combining many nuclei into a nucleus.
    It can be controlled.It cannot be controlled.
    Atom bombs are made on this principle.Nuclear bombs are made on this principle.
    Comparatively, less energy is produced.Comparatively, more energy is produced.

    c. Biomass and biogas.

    Biomass is the source of biogas.Biogas is the product of biomass.
    It is an energy source.It is energy.
    Cattle dung, sewage, etc. are biomass.Electricity or heat are biogas results.

    d. Wind energy and tidal energy.

    Wind energyTidal energy
    The energy generated using the currents of wind.The energy generated using the currents of tides on the sea.
    The wind rotates the turbine here.The water rotates the turbine here.
    It is used for pumping, sailing, etc.It is used for electricity generation.

    e. Solar energy and fuel energy.

    Solar energyFuel energy
    The energy produced by using the heat and light energy of the sun is solar energy.The energy produced by using fuels formed from fossils is fuel energy.
    It is the main source of energy.It is an alternative source of energy.
    It is formed on the sun.It is formed under the earth's crust.

  23. We all know, Nepal is a country that is rich enough in water resources. Hundreds of fast-flowing rivers are found in our country. And water is the main agent to produce hydroelectricity. Due to the presence of many large and small rivers & rivulets, we have the high potentiality of generating electricity. But it is very difficult to construct hydropower stations in the various parts of the country because of the difficult topography. The absence of infrastructural facilities is the major cause of it. Not only we are lacking transportation, communication, and other facilities but also there is a shortage of skill human resources and advanced technology. Therefore, we are unable to generate the electricity meeting our potential limit. Hence, Nepal has a high potential for producing hydroelectricity but it is difficult to produce.

  24. The energy present in the body of a dead person doesn't escape instantly but stays in the body.

    Later when the body is buried, it decays and the energy is released to the soil. If the body is burnt instead, the energy is released to atmosphere. This is a part of carbon cycle.