Energy
Grade 9 Science Resource
What is Energy?
Energy is defined as the capacity of doing work.
Units of Energy
The SI unit of Energy is Joule and CGS Unit is Ergs.
Sources of Energy
There are two different types of energy sources:
- Primary Source of energy
- Secondary Source of energy
Primary Sources
These are the sources of energy that can be used in the same form that they exist in nature. For example firewood.
Secondary Sources
These are the sources of energy that are derived from primary sources of energy. For example mineral oil.
Renewable vs Non-Renewable Energy
Renewable Energy
Those sources of energy which will be exhausted after their continuous use but can be renewed by natural ways. For example: Biomass, Water, Forest etc.
Non-Renewable Energy
Those sources of energy which will be exhausted after their continuous use and can't be renewed by natural ways. For example: fossils, fuels, natural gas etc.
Perpetual Sources of Energy
Those sources of energy, which neither decrease nor increase but remain unaffected despite of their continuous use. For Example: solar energy, wind energy etc.
The Sun: Ultimate Source of Energy
The Sun is the main source of energy. It provides tremendous amount of energy for Earth every second at the rate of 1.4kW per square meter.
Most forms of energy that we use on the Earth surface are forms of solar energy. Wind energy, fossil energy, hydroelectricity, tidal energy, geothermal energy etc. are all direct or indirect forms of solar energy.
How is hydroelectricity a form of solar energy?
The solar heat evaporates water from oceans, seas and other water sources. This water vapor forms clouds which result in rainfall. This water can be used to generate hydroelectricity.
How is wind energy a form of solar energy?
The Sun heats the air near the Earth's surface. Hot air rises, creating a partial vacuum. Air from neighboring areas moves toward this space, causing wind.
Nuclear Energy
The energy produced during the breakdown (called fission) and building up (called fusion) of nucleus is called nuclear energy.
Nuclear Fission
The process of breaking down of heavy nucleus into lighter nuclei with release of tremendous energy.
Example: Uranium nucleus splitting
Nuclear Fusion
The process of fusion of two or more lighter nuclei to form heavier nuclei with release of tremendous energy.
Example: Fusion of hydrogen atoms in the Sun
Einstein's Mass-Energy Relation
E = mc²
Where 'E' is energy, 'm' is mass, and 'c' is the speed of light. This equation shows that mass can be converted into energy.
Fossil Fuels
Fossil fuels are obtained from the dead remains of plants and animals over millions of years. Examples: coal, mineral oil, natural gas.
Advantages
- Cheaper and available everywhere
- Portable
- Easy to store and convenient to use
Disadvantages
- Produces smoke and harmful gases causing air pollution
- Non-renewable resource that will be exhausted soon
Hydroelectric Energy
The energy of water flowing in rivers or stored in dams is called hydroelectric energy.
Advantages
- Cheaper in the long term
- Supplies energy without pollution
- Renewable source of energy
- Essential for computers and modern electronics
Disadvantages
- Affects aquatic life
- May submerge fertile land
- Risk of fatal electric shock
- Not convenient for running vehicles
Nepal's Hydroelectric Potential
Nepal has an estimated electricity generation capacity of 83,000 megawatts. Nepal is rich in water resources and has high potential for hydroelectricity, but development is challenging due to lack of skilled manpower and financial resources.
Energy Crisis
The shortage or scarcity of fuels in the near future due to the exhaustion of their stock is called energy crisis.
Causes
- Excessive use of fuels due to overpopulation
- Use of non-renewable natural resources
- Lack of development of alternative energy sources
Solutions
- Use conventional energy sources wisely
- Develop and use alternative energy sources
- Develop modern technology for alternative energy
- Control population growth and raise awareness
Alternative Energy Sources
Biomass Energy
Energy from agricultural residue, animal waste, wood etc. Used in rural areas as straw, stalks, husk, firewood, animal dung.
Biogas
Mixture of methane, CO₂, hydrogen and hydrogen sulfide produced by anaerobic decomposition of animal or plant waste.
Wind Energy
Energy from blowing wind. In Nepal, it can be obtained in the Mahabharat region.
Geothermal Energy
Heat energy from the Earth's interior. Hot rocks heat underground water turning it into steam that can generate electricity.
1 Comments
Nepali S. Hub 09 Dec 2025 at 01:12 PM
Understanding and classified
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