Solution
The phenomenon where hot water freezes faster than cold water is known as the Mpemba effect. While complex, the primary physical reasons attributed to this in standard physics contexts are:
- Evaporation (Reason III): Hot water evaporates at a much faster rate than cold water. This evaporation removes mass from the water. Since there is less mass to cool down and freeze, the process can occur faster. Additionally, evaporation removes latent heat, aiding cooling.
- Rate of Heat Loss (Reason II): According to Newton’s Law of Cooling, the rate of heat loss is directly proportional to the temperature difference between the object and the surroundings ($ \frac{dQ}{dt} \propto (T – T_s) $). Initially, the hot water has a much larger temperature difference with the freezing air, leading to a significantly higher initial rate of heat loss compared to the cold water.
Therefore,answer given in book is: both the initial rapid rate of cooling and the mass loss due to evaporation contribute to this effect.
Correct Option: (c) Reasons II and III