2024 · Q102
On a day when I am in hurry to go to office, I have a fixed quantity of rice which was just cooked and kept in a bowl. In order to cool it quickly, which one of the following is the best option?
General KnowledgePhysics
- ALet it be kept on the table in a room where there is no fan, no air conditioner
- BLet it be kept in a room with AC set at a temperature around 23 °C and a ceiling fan (or table fan) operating at slow speed
- CLet it be kept in a bowl of water (at room temperature) and operating a ceiling fan (or table fan) at full speed
- DLet it be kept in a bowl of water at room temperature only
Explanation
Cooling is fastest when heat transfer from the rice is maximised. Placing the bowl in water at room temperature gives conductive heat loss from all sides of the bowl, and running a fan at full speed maximises convective and evaporative heat loss from the water surface and the rice surface. Options relying on still air, air-conditioning alone, or water without airflow all cool more slowly. The answer is (C).