CAPF AC 2021 Q3: Science & Technology – Physics
Which electromagnetic radiation(s) is/are used to cook food?
- (a) Infrared radiation only
- (b) Microwave radiation only
- (c) Infrared and microwave radiations
- (d) All electromagnetic radiations
Answer: (c) Infrared and microwave radiations
Explanation
Radiations used to cook food
How to think: think of the kitchen appliances you know.
A microwave oven uses microwaves.
A grill, toaster or tandoor cooks with heat radiation, which is infrared.
So two radiations cook food, not one.
| Radiation | How it cooks | Where it is used |
|---|---|---|
| Microwaves | Make water molecules in food vibrate, which produces heat inside the food | Microwave oven |
| Infrared | Carries heat to the surface of the food | Grill, toaster, tandoor, charcoal fire, infrared cooker |
Why not the others:
| Radiation | Main use |
|---|---|
| Radio waves | Communication |
| Ultraviolet | Killing germs, water purifiers |
| X-rays | Medical imaging |
| Gamma rays | Cancer treatment, sterilising food (it does not cook it) |
Answer: (c) Infrared and microwave radiations.
Why each option is right or wrong
- (a) Incorrect. Microwave ovens also cook food, so infrared is not the only one.
- (b) Incorrect. Grills, toasters and tandoors cook with infrared heat radiation.
- (c) CORRECT. Infrared heats the surface and microwaves heat the water inside the food.
- (d) Incorrect. Radio waves, X-rays and gamma rays are not used for cooking.
Key point
Two radiations cook food: infrared (heat radiation: grill, toaster, tandoor) and microwaves (microwave oven, heats water molecules).
Remember
Cooking = infrared (heat) + microwaves.
Common mistakes
- Marking microwave only because the oven carries that name.
- Forgetting that ordinary heat radiation from a fire or grill is infrared.
- Thinking gamma rays cook food; they only sterilise and preserve it.
Exam tip
Educated guess: the word only in (a) and (b) is risky, and all in (d) is too wide. That leaves (c).
Sources
- NCERT Class XII Physics — Electromagnetic Waves (electromagnetic spectrum)
- NCERT Class VII Science — Heat (radiation)