Question

Which of the following is used as a coolant in an automobile radiator as well as a heater in hot water bags?
A) Ice
B) Sand
C) Water
D) All of these

Answer 1

Hint: Radiators are used in automobiles, locomotives, motorcycles and other internal combustion engines as heat exchangers. A liquid called engine coolant is circulated through the block of the engine, gets heated and is then returned to the engine. Hot water bags are rubber made and have a stopper at their mouth. They are filled with a warm liquid and serve as pain relief aids that relieve discomfort through heat therapy.

Complete step by step solution:
The amount of heat absorbed or given out by any substance depends upon the specific heat of the substance. For a given change in temperature, a body having higher specific heat will absorb and release more heat than a body having comparatively lower specific heat. Since the working of radiators depends on the absorption of heat from the engine and the working of hot water bags depends on the release of heat to the body of a person, the liquid used in these devices should have a higher specific heat.

As compared to any other liquid, water has the highest specific heat. The circulating water through radiators thus absorbs very high amounts of heat and keeps the engine from overheating. On the other hand, when water is used in hot water bags, it loses heat slowly and keeps the bag warm for a long time.

Hence, we can say that option (C) is the correct answer.

Note: Higher specific heat means a higher heat transfer for the same change in temperature. A higher heat transfer should not be confused with a higher change in temperature, because that would be a defeat of the purpose of using a high specific heat liquid as coolant or heater.