A solar water heater cannot be used to get hot water on:
(a) A sunny day
(b) A cloudy day
(c) A hot day
(d) A windy day
Answer: (b) A cloudy day
Explanation: A solar water heater works by absorbing direct sunlight to heat water. On a cloudy day, the sun is blocked by clouds, reducing the solar radiation significantly, so it cannot heat water effectively.
[Image of solar water heater working diagram]
Q2
Which of the following is not an example of a biomass energy source?
(a) Wood
(b) Gobar-gas
(c) Nuclear energy
(d) Coal
Answer: (c) Nuclear energy
Explanation: • Wood, Gobar-gas, and Coal are all derived from living organisms (plants/animals), so they are biomass sources (Coal is fossilized biomass).
• Nuclear energy comes from the fission of heavy atoms like Uranium, not from biological matter.
Q3
Most of the sources of energy we use represent stored solar energy. Which of the following is not ultimately derived from the Sun?
(a) Geothermal energy
(b) Wind energy
(c) Nuclear energy
(d) Biomass
Answer: (c) Nuclear energy
Explanation: • Wind: Caused by uneven heating of Earth by the Sun.
• Biomass: Plants grow using sunlight (photosynthesis).
• Geothermal: Though largely internal heat, some definitions debate this, but strictly speaking, Nuclear Energy is the clearest outlier as it originates from the binding energy of atoms formed during the creation of the universe/stars, not current solar radiation.
Note: Geothermal energy is also not derived from the sun (it is from Earth’s core), but in NCERT options, Nuclear is usually the intended answer for “Not Solar”.
Q4
Compare and contrast fossil fuels and the Sun as direct sources of energy.
Fossil Fuels (Coal/Petroleum)
1. Non-renewable (Finite source).
2. Causes pollution (releases CO₂, SO₂).
3. Expensive to mine and transport.
4. Available on demand (can be used anytime).
The Sun (Solar Energy)
1. Renewable (Inexhaustible source).
2. Pollution-free (Clean energy).
3. Free source, but setup is costly.
4. Intermittent (only available during the day).
Q5
Compare and contrast biomass and hydroelectricity as sources of energy.
Similarities: Both are renewable sources of energy.
Differences:
Biomass (e.g., Biogas)
• Generates pollution if burnt directly (wood).
• Biogas is clean but small scale.
• Requires waste management.
Hydroelectricity
• Pollution-free operation.
• Large scale power generation.
• Dams cause ecological damage and displacement of people.
Q6
What are the limitations of extracting energy from: (a) the wind? (b) waves? (c) tides?
(a) Wind Energy: 1. Needs a minimum wind speed of 15 km/h.
2. Requires vast areas of land for wind farms.
3. High initial setup cost.
(b) Wave Energy: 1. Viable only where waves are very strong.
2. Technology is expensive and prone to corrosion from sea water.
(c) Tidal Energy: 1. Locations for building dams on narrow bays are very limited.
2. Power generation is not continuous (depends on tide timings).
Q7
On what basis would you classify energy sources as (a) Renewable and Non-renewable? (b) Exhaustible and Inexhaustible?
(a) Renewable vs Non-renewable: • Renewable: Replenished by nature continuously (e.g., Solar, Wind).
• Non-renewable: Cannot be replenished quickly once used (e.g., Coal, Petroleum).
(b) Exhaustible vs Inexhaustible: • Exhaustible: Finite stock, will finish one day (Coal).
• Inexhaustible: Unlimited supply, will never finish (Sunlight).
(Essentially, these two classifications overlap significantly).
Q8
What are the qualities of an ideal source of energy?
An ideal source of energy should be:
1. Efficient: Does a large amount of work per unit volume/mass (High calorific value).
2. Accessible: Easy to get.
3. Transportable: Easy to store and transport.
4. Economical: Low cost.
5. Clean: Causes minimal environmental pollution.
Q9
What are the advantages and disadvantages of using a solar cooker? Are there places where solar cookers would have limited utility?
Advantages: • Saves fuel.
• Pollution-free.
• Nutrients in food are not destroyed (slow cooking).
Disadvantages: • Slow cooking process.
• Cannot be used at night or cloudy days.
• Direction of reflector must be constantly adjusted towards the Sun.
Limited Utility: Places with frequent cloud cover, heavy rainfall, or very short days (poles) are not suitable.
[Image of box type solar cooker diagram]
Q10
What are the environmental consequences of the increasing demand for energy? What steps would you suggest to reduce energy consumption?
Consequences: 1. Increased burning of fossil fuels $\rightarrow$ Global Warming & Acid Rain.
2. Deforestation for firewood.
3. Destruction of ecosystems for dams and mines.
Steps to Reduce Consumption: 1. Use public transport or carpooling.
2. Switch to energy-efficient appliances (LEDs).
3. Use renewable sources like Solar Water Heaters.
4. Prevent wastage (Switch off lights when not in use).