UPSC Prelims 2015 Q95: Science & Technology – Energy & Environment
With reference to 'fuel cells' in which hydrogen - rich fuel and oxygen are used to generate
electricity, consider the following statements:
1. If pure hydrogen is used as a fuel, the fuel cell emits heat and water as by - products.
2. Fuel cells can be used for powering buildings and not for small devices like laptop computers.
3. Fuel cells produce electricity in the form of Alternating Current (AC).
Which of the statements given above is/are correct?
- (a) 1 only
- (b) 2 and 3 only
- (c) 1 and 3 only
- (d) 1, 2 and 3
Answer: (a) 1 only
Explanation
Fuel cells
A fuel cell turns the chemical energy of hydrogen and oxygen straight into electricity.
| Statement | Verdict | Fact |
|---|---|---|
| 1. If pure hydrogen is used as a fuel, the fuel cell emits heat and water as by-products | Correct | Hydrogen plus oxygen gives water, heat and electricity |
| 2. Fuel cells can be used for powering buildings and not for small devices like laptop computers | Incorrect | They can power small devices as well as vehicles and buildings |
| 3. Fuel cells produce electricity in the form of Alternating Current (AC) | Incorrect | They produce Direct Current (DC) |
Fuel cell and battery compared:
| Feature | Fuel cell | Battery |
|---|---|---|
| Fuel | Supplied continuously from outside | Stored inside |
| Runs | As long as fuel is fed | Until it is discharged |
| Output | DC | DC |
Answer: (a) 1 only.
Why each option is right or wrong
- (a) CORRECT. With pure hydrogen, a fuel cell gives only heat and water as by-products.
- (b) Incorrect. Fuel cells can power small devices, and they give DC, not AC.
- (c) Incorrect. Statement 3 is false; the output is Direct Current.
- (d) Incorrect. Statements 2 and 3 are false.
Key point
Fuel cell: hydrogen + oxygen gives electricity (DC), water and heat; runs as long as fuel is supplied; used in vehicles, buildings and small devices.
Remember
Fuel cell: hydrogen in, water out, DC electricity.
Common mistakes
- Thinking fuel cells give AC like a generator.
- Believing they are only for large uses.
- Confusing a fuel cell with burning hydrogen; there is no combustion.
Exam tip
All cells and batteries give DC. AC needs an inverter or a rotating generator.
Sources
- Ministry of New and Renewable Energy — National Green Hydrogen Mission (fuel cell applications)
- NCERT Class XII — Chemistry, Ch 2 (Electrochemistry: fuel cells)