UPSC Prelims 2010 Q88: Science & Technology – Physics
What is the principle by which a cooling system (Radiator) in a motor car works?
- (a) Conduction only
- (b) Convection
- (c) Radiation only
- (d) Both conduction and radiation
Answer: (b) Convection
Explanation
How a car radiator's cooling system works
A car's radiator removes heat from the engine coolant primarily through airflow-driven heat transfer.
| Option | Verdict | Reason |
|---|---|---|
| (a) Conduction only | Incorrect | Conduction alone doesn't capture the radiator's main cooling mechanism, which depends heavily on moving air |
| (b) Convection | Correct | The radiator's fins transfer heat to the surrounding air, which is continuously moved (by the car's motion and the cooling fan), carrying heat away — this moving-fluid heat transfer is the defining process of convection |
| (c) Radiation only | Incorrect | Radiation plays only a minor role; it is not the dominant cooling mechanism |
| (d) Both conduction and radiation | Incorrect | This omits convection, which is the actual dominant principle; conduction and radiation alone don't explain the radiator's airflow-dependent cooling |
Radiator cooling mechanism:
| Point | Detail |
|---|---|
| Dominant principle | Convection — heat carried away by moving air |
| Supporting role | Conduction moves heat from coolant to the fins; radiation plays a minor part |
| Why airflow matters | Fan/car-motion-driven air movement is what makes a radiator work |
Answer: (b) Convection.
Why each option is right or wrong
- (a) Incorrect. Conduction alone doesn't capture the radiator's main, airflow-dependent cooling process.
- (b) CORRECT. The radiator's cooling is governed mainly by convection: heat is carried away by air continuously moving across its fins.
- (c) Incorrect. Radiation plays only a minor role, not the dominant cooling mechanism.
- (d) Incorrect. This excludes convection, the actual dominant principle behind radiator cooling.
Key point
A car radiator's cooling system works mainly on the principle of CONVECTION — heat is transferred to moving air (via the fan and car's motion), which carries it away from the radiator fins.
Remember
A car radiator's cooling system works mainly through convection — heat transfer to continuously moving air.
Common mistakes
- Underestimating convection's role and assuming conduction or radiation dominates instead.
- Missing that moving air (not just radiating heat or direct metal contact) is what drives most of the cooling.
- Combining conduction and radiation while leaving out convection, the actual primary mechanism.
Exam tip
Radiator cooling = convection (heat carried away by moving air through the fan and car's motion). The dominant, correct principle here.
Sources
- NCERT Class XI Physics — Thermal Properties of Matter (heat transfer)
- H. C. Verma — Concepts of Physics, Volume 2 (Heat Transfer)