Conventional Sources: Fossil Fuels & Thermal Power - UNSOLVED PRACTICE SET
Chapter: Sources of Energy | Topic: Conventional Sources Fossil Fuels Thermal Power
CONVENTIONAL SOURCES: FOSSIL FUELS & THERMAL POWER - UNSOLVED PRACTICE SET
Topic: Conventional Sources Fossil Fuels Thermal Power
Multiple Choice Questions
Q1. Fossil fuels (coal, petroleum, natural gas) are formed from:
- Volcanic rock cooling over centuries
- The decomposition of dead plants and animals buried under the Earth's crust over millions of years
- Ocean water evaporation
- Chemical reactions in factories
Q2. Fossil fuels are classified as non-renewable resources because:
- They can be regenerated within a few months
- They take millions of years to form and are being consumed much faster than they form
- They are made artificially
- They produce no energy when burnt
Q3. In a thermal power plant, the primary energy conversion sequence is:
- Chemical energy → Electrical energy directly, with no intermediate steps
- Chemical energy (fuel) → Heat energy → Mechanical energy (turbine) → Electrical energy (generator)
- Solar energy → Mechanical energy → Electrical energy
- Nuclear energy → Light energy → Electrical energy
Q4. Burning fossil fuels releases large amounts of which gas, contributing significantly to global warming?
- Oxygen
- Nitrogen
- Carbon dioxide
- Helium
Q5. Which of the following is NOT a fossil fuel?
- Coal
- Petroleum
- Natural gas
- Biogas
Q6. A major disadvantage of thermal power plants based on coal is:
- They produce zero pollution
- They are located only in coastal areas
- They release pollutants (SO₂, NOx, particulate matter) and CO₂, contributing to air pollution and climate change
- They cannot generate electricity at all
Short Answer Questions
Q7. What are fossil fuels? Name three examples and briefly describe how they are formed.
Q8. Why are fossil fuels called 'non-renewable' sources of energy? What does this imply for future generations?
Q9. Describe, in sequence, the energy transformations that occur in a coal-based thermal power plant, from coal to electricity reaching a home.
Q10. India has several large thermal power plants (e.g., in regions with coal deposits like Jharkhand, Chhattisgarh, Odisha). What environmental concerns are associated with these plants?
Q11. What is meant by 'depletion' of fossil fuel reserves? Why are scientists and governments worldwide concerned about this?
Q12. Name two pollutant gases released by burning coal and explain one health effect of each on people living near thermal power plants.
Long Answer Questions
Q13. Describe the working of a coal-based thermal power plant in detail. Your answer must cover:
(a) where coal comes from and how it is stored/transported to the plant,
(b) the combustion of coal to produce heat,
(c) how this heat is used to convert water into high-pressure steam,
(d) how the steam drives a turbine connected to a generator (recall the generator principle from your earlier chapter), and
(e) what happens to the steam after it passes through the turbine (the role of the cooling/condenser system).
Q14. India relies on coal for a significant portion of its electricity generation, even though coal is a polluting and non-renewable resource.
(a) Why might a country continue to rely heavily on coal despite these drawbacks (consider cost, existing infrastructure, employment)?
(b) What are the long-term risks of this continued reliance — both environmental and in terms of energy security?
(c) What steps can be taken to reduce the negative impact of existing coal plants (e.g., technology upgrades) while transitioning to other sources?
(d) Why is this transition described as 'gradual' rather than 'immediate' in most countries, including India?
Q15. Compare and contrast a thermal power plant running on coal with one running on natural gas (both are 'conventional' fossil fuel sources).
(a) Both ultimately use heat to produce steam and drive a turbine — what is different about the fuel used?
(b) Compare the two in terms of: ease of transport, pollution levels (natural gas burns more cleanly than coal), and calorific value.
(c) Why might a country want to shift its thermal power generation from coal to natural gas as an 'intermediate' step, even though natural gas is still a fossil fuel?
(d) What is the ultimate long-term goal beyond even natural gas, in terms of types of energy sources?
Numerical / Application-Based Problems
Q16. A thermal power plant has an overall efficiency of 35% (only 35% of the heat energy from burning coal is converted to electrical energy; the rest is lost mainly as waste heat).
(a) If the plant burns coal that releases 1000 MJ (megajoules) of heat energy, how much electrical energy (in MJ) is produced?
(b) How much energy is 'lost' as waste heat?
(c) If a newer plant design improves efficiency to 45%, how much electrical energy would be produced from the same 1000 MJ of heat?
(d) Calculate the percentage increase in useful electrical output due to this efficiency improvement.
Q17. A coal-fired power plant burns 500 tonnes of coal per day. If the calorific value of this coal is 25,000 kJ/kg, and the plant's overall efficiency is 30%:
(a) Calculate the total heat energy released per day (in kJ). [1 tonne = 1000 kg]
(b) Calculate the electrical energy output per day (in kJ), given 30% efficiency.
(c) Convert this electrical energy to kWh (1 kWh = 3.6 × 10⁶ J = 3.6 × 10³ kJ).
Q18. India's coal reserves are estimated to last a certain number of years 'at current consumption rates' — but consumption is increasing every year.
(a) If current reserves would last 100 years at today's consumption rate, but consumption increases by 5% every year, would the reserves actually last 100 years, more, or less? Explain your reasoning (you do not need to calculate the exact number).
(b) This concept applies to all non-renewable resources. Why is it misleading to say 'we have X years of coal left' without specifying the assumed consumption rate?
(c) How does this relate to the urgency of developing renewable energy sources?