Consider the following statements and identify the correct answer using the code given below : 1. In a thermal power station, fuels such as oil, coal or natural gas are used to generate electricity. 2. Fuels are burned to heat water and turn it into steam, which goes through a turbine, which spins and turns, generating electricity. Code:
- (a)Statement 1 is correct but statement 2 is not correct
- (b)Statement 2 is correct but statement 1 is not correct
- (c)Both the statements are correct and statement 2 explains statement 1
- (d)Both the statements are correct but statement 2 does not explain statement 1
Correct — C, Both the statements are correct and statement 2 explains statement 1. Statement 1 says what a thermal power station does — it burns oil, coal or natural gas to generate electricity. Statement 2 says how it does it — the fuel heats water into steam, the steam drives a turbine, and the spinning turbine turns a generator that produces the current. The second is not an independent fact standing beside the first; it is the mechanism by which the first is true, which is exactly what the phrase 'statement 2 explains statement 1' asks you to certify. Notice the chain of energy conversions hidden in the two lines: chemical energy in the fuel becomes heat, heat becomes the kinetic energy of steam and then of the rotating turbine, and electromagnetic induction in the generator turns that rotation into electrical energy.
- (a)Statement 1 is correct but statement 2 is not correct — Statement 2 is not wrong. The boiler, steam, turbine and generator sequence is precisely how a coal- or oil-fired station works, and it is the standard school description.
- (b)Statement 2 is correct but statement 1 is not correct — Statement 1 is not wrong either. Oil, coal and natural gas are the three fuels used in thermal stations, and in India coal dominates that group.
- (d)Both the statements are correct but statement 2 does not explain statement 1 — The tempting near-miss. It concedes that both statements are true but denies the explanatory link, and the link is plainly there — statement 2 describes the machinery by which the burning of fuel in statement 1 ends as electricity.
A conventional thermal power station is a heat engine. Fuel is burned in a boiler, the heat raises high-pressure steam, the steam expands through a turbine and spins it, the turbine shaft drives an alternator, and the alternator converts mechanical rotation into electricity by electromagnetic induction. Spent steam is condensed and returned to the boiler, which is why such stations need very large volumes of cooling water and are usually sited near a river or on the coast. Coal supplies most of India's thermal generation, which is why coal-fired plants cluster near the coalfields of Jharkhand, Odisha, Chhattisgarh and West Bengal or at ports that can receive imported coal.
Assertion-and-reason items of this type are decided in two steps, and candidates lose the mark at the second. First check each statement independently; here both survive. Then ask whether the second statement is the cause or mechanism of the first, or merely a second true fact about the same subject. A useful test is to insert the word 'because' between them and see whether the sentence reads sensibly — a thermal station generates electricity from fuel because the fuel raises steam that spins a turbine, which reads perfectly, so the explanatory link holds and the answer is (c) rather than (d). One honest qualification worth knowing: the steam route described in statement 2 is the route for coal and oil, and for the steam half of a combined-cycle gas plant, but an open-cycle gas turbine burns gas and expands the combustion products through the turbine directly, without raising steam. The statement is the standard description rather than a universal one.
- The energy chain in a thermal station runs chemical to heat to kinetic to electrical.
- Steam raised in the boiler drives a turbine, and the turbine drives an alternator that generates electricity by electromagnetic induction.
- Condensers and cooling water are essential to the cycle, which is why thermal stations are sited near a reliable water source.
- Coal is the dominant thermal fuel in India, and coal-fired capacity is the largest single block in the national generation mix.
- Burning coal releases oxides of sulphur and nitrogen, the chief precursors of acid rain, along with carbon dioxide and particulates.
- Choosing 'both true but not the explanation' when the second statement is plainly the mechanism of the first.
- Treating every gas-fired station as a steam plant; an open-cycle gas turbine does not raise steam.
- Confusing the turbine, which spins, with the generator, which is where the electricity is actually produced.
As a two-statement item with a code that separates 'both true and 2 explains 1' from 'both true but 2 does not explain 1' — the distinction the whole question is built on.
Assertion (A): Coal-based thermal power stations contribute to acid rain. Reason (R): Oxides of carbon are emitted when the coal burns.
- (a) Both A and R are individually true and R is the correct explanation of A
- (b) Both A and R are individually true but R is NOT the correct explanation of A
- (c) A is true but R is false
- (d) A is false but R is true
Answer(b) Both A and R are individually true but R is NOT the correct explanation of A
The same coal-fired plant and the same code, resolved the other way. There both statements are true but the reason names the wrong emission, so the explanatory link fails. Reading the two items together shows exactly where the distinction between the last two options lies.
Consider the following: 1. Carbon dioxide 2. Oxides of Nitrogen 3. Oxides of Sulphur Which of the above is/are the emission/emissions from coal combustion at thermal power plants?
- (a) 1 only
- (b) 2 and 3 only
- (c) 1 and 3 only
- (d) 1, 2 and 3
Answer(d) 1, 2 and 3
The output side of the same plant. Once the fuel-to-boiler-to-turbine chain is clear, the emissions follow from what is being burned, and all three of those gases come out of a coal furnace.
- practice — not a real PYQ
In a coal-fired thermal power station, electricity is generated in which of the following devices?
- (a)The boiler
- (b)The turbine
- (c)The alternator
- (d)The condenser
Answer(c) The alternator — the turbine only spins the shaft; the alternator converts that rotation into electricity by electromagnetic induction.
- practice — not a real PYQ
The energy conversion sequence in a conventional thermal power plant is
- (a)chemical to electrical to heat to kinetic
- (b)chemical to heat to kinetic to electrical
- (c)heat to chemical to kinetic to electrical
- (d)kinetic to heat to chemical to electrical
Answer(b) chemical to heat to kinetic to electrical — fuel to boiler to turbine to alternator.