PYQs
Practise questions grouped by chapter and source year.
Practice questions are organised using the years and labels in our source collection. Work through the solutions with your teacher; these are not a complete official examination paper.
Practice question 1
Source year: 20252 marksWhat is a good source of energy? Write two characteristics of a good source of energy. [CBSE 2025]
Practice question 2
Source year: 20243 marksCompare and contrast fossil fuels and renewable sources of energy. Write any four points. [CBSE 2024]
Practice question 3
Source year: 20233 marksExplain the principle of solar cooker. Write two advantages and two limitations of using solar cooker. [CBSE 2023]
Practice question 4
Source year: 20223 marksWhat is biogas? Write the composition of biogas. State two advantages of biogas over fossil fuels. [CBSE 2022]
Practice question 5
Source year: 20213 marksDescribe how energy from the sea can be harnessed. Write any two limitations of ocean thermal energy. [CBSE 2021]
Formulae
Revisit important relationships and quick revision formulae.
Energy from Various Sources
Fossil Fuels: Coal, Petroleum, Natural Gas Renewable: Solar, Wind, Hydro, Biomass, Geothermal Nuclear: Uranium-235, Plutonium-239
Solar Energy Efficiency
Solar cell efficiency: 15-25% Solar cooker temperature: 100-140°C Solar panel output: ~200W/m²
Wind Energy
Minimum wind speed: 15 km/h Kinetic energy: E = ½mv² Power ∝ v³ (wind speed)
Biogas Composition
Methane (CH₄): 50-75% Carbon dioxide: 25-50% Small amounts: H₂, N₂, H₂S
Derivations
Work through the reasoning behind key concepts.
Characteristics of Good Energy Source
- High calorific value (energy per unit mass)
- Easy availability and transport
- Economic (affordable)
- Less pollution
- Easy storage
Solar Cooker Working
Principle: Greenhouse effect
- Black surface absorbs heat
- Glass traps heat (prevents convection)
- Reflector concentrates sunlight
- Temperature rises to 100-140°C
Hydroelectric Power Plant
Potential energy of water → Kinetic energy Water falls from height h Turbine rotates → Generator produces electricity P = mgh/t (Power output)
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