Question

Give one example where a specific heat capacity of water is used as a heat reservoir.
A. Water remains hot in bottle for a long time
B. Water remains cold in bottle for long time
C. Water remains hot in bottle for some time
D. None of these

Answer 1

Recall the definition of specific heat capacity. It measures the amount of heat needed to be given to the substance of mass 1 kg to raise its temperature by $1\,^\circ {\text{C}}$. The specific heat of water is high, that is $4186\,{\text{J/kg}}\,^\circ {\text{C}}$.

Complete step by step answer:
As we know the heat capacity of the water that is the heat energy required to raise the temperature of water by $1\,^\circ {\text{C}}$ is $4186\,{\text{J/kg}}\,^\circ {\text{C}}$. Also, the same amount of energy should be drawn from the water to decrease its temperature by $1\,^\circ {\text{C}}$. If we compare the heat capacity of water with the heat capacity of any other liquid, the heat capacity of the water is highest. Thus, water takes longer to cool compared to any other liquid.

In the heat reservoir, the water is kept at high temperature and since the water does not cool for a reasonable amount of time, we get heat energy as long as the water is hot. As we know, the hot water releases 4186 J of heat energy for $1\,^\circ {\text{C}}$ decrease in its temperature and thus the water is mainly used in the heat reservoir technique.

So, the correct answer is option A.

Note: Water has the highest specific heat capacity therefore it takes a longer time to heat and a long time to cool. The question specifically talks about specific heat capacity being used as a heat reservoir. If we have the steam of water at $1\,00^\circ {\text{C}}$, the heat released by the heat is in the two forms: the latent heat released by the steam to convert the state of the steam into the water at constant temperature and energy released by the water at $1\,00^\circ {\text{C}}$ during cooling due to its specific heat capacity.