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General Science · Class 10 · Chapter 7: Energy

8 min

Key points

Energy is the ability to do work and is measured in Joules (J)
Kinetic Energy = ½mv² where m is mass and v is velocity
Potential Energy = mgh where m is mass, g is acceleration due to gravity, and h is height
Law of Conservation of Energy: Energy can neither be created nor destroyed, it can only be transformed from one form to another
Renewable energy sources include solar, wind, hydro, and biomass while non-renewable sources include coal, oil, and natural gas
Pakistan's major hydroelectric projects include Tarbela Dam, Mangla Dam, and Warsak Dam
Thermal energy is the internal energy of a substance due to random motion of its molecules
Nuclear energy is released during nuclear fission and fusion reactions
Efficiency = (Useful Energy Output / Total Energy Input) × 100%

Definitions

Energy: Energy is the capacity or ability to do work
Kinetic Energy: The energy possessed by a body due to its motion
Potential Energy: The energy possessed by a body due to its position or configuration
Renewable Energy: Energy sources that can be replenished naturally in a short period of time
Non-renewable Energy: Energy sources that cannot be replenished once they are exhausted

Worked example

Define energy and state the law of conservation of energy. Give two examples of energy transformation. (6 marks)

Energy is defined as the capacity or ability to do work. The law of conservation of energy states that energy can neither be created nor destroyed but can only be transformed from one form to another, and the total energy of an isolated system remains constant. Example 1: In a hydroelectric power plant, potential energy of water is converted to kinetic energy, then to electrical energy. Example 2: In photosynthesis, light energy is converted to chemical energy.

Common mistakes

Students confuse kinetic energy with potential energy - remember KE is due to motion, PE is due to position
Always write the complete formula before substituting values in numerical problems
Don't forget to convert units to SI system before calculation (kg, m, s)
Students mix up renewable and non-renewable energy sources
Always state the law of conservation of energy exactly as given in textbook

Quick recap

Energy is the capacity to do work and exists in various forms like kinetic, potential, heat, light, sound, chemical and electrical. The law of conservation of energy states energy cannot be created or destroyed, only transformed. Common transformations include potential to kinetic energy in falling objects, and chemical to electrical energy in batteries. Renewable sources like solar and wind are unlimited while non-renewable sources like fossil fuels are limited.

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