Question

Water is used in hot bottles for fomentation (therapeutic application of warmth to relieve pain). Give reason.
A) Water remains hot in the bottle for a long time.
B) Water remains cold in the bottle for a long time.
C) Water remains hot in the bottle for a short time.
D) Water remains cold in the bottle for a short time.

Answer 1

Hint: The duration of hot or cold of the substance depends on the specific heat of the substance. If the specific heat of a substance is high then it takes more time to become hot and more time to become cold. If the specific heat of the substance is low then it takes less time to become hot and less time to become cold.

Complete answer:
The specific heat of the water is very high, so it takes more time for heating and takes more time to become cold. The heated water in the glass bottle remains hot for a long time and takes more time to become cold.
Therefore, the water is used in hot bottles for fomentation because the water remains hot in the bottle for a long time and the option (A) is correct.

Additional Information: The specific heat is defined as the heat required increasing the unit temperature of unit mass. Water requires more energy than other substances to raise its temperature by one degree Celsius, so the specific heat of water is high. The latent heat is defined as the heat requires changing the phase of the substance. The temperature remains constant during phase change.

Note: Be careful in using the water in the bottles for therapeutic application as water takes more time to become cold and it may burn the skin. The heat transfer from glass bottles to human skin occurs very easily because the glass adopts the water temperature rapidly.