UPSC Prelims 2002·GS1·science-and-technology·science and technology

A hollow sphere of radius R, a hollow cube of side R and a thin circular plate of radius R, made up of the same material, are all heated to 20°C above room temperature. When left to cool in the room, which of them will reach the room temperature first?

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Last updated 23 May 2026, 3:31 pm IST
  1. ACircular plateCorrect
  2. BCube
  3. CSphere
  4. DAll of them will reach the room temperature at the same time

Explanation

The rate of cooling of an object depends on its surface area to volume ratio. The thin circular plate has the largest surface area relative to its very small volume and mass. Because it is thin, it has two large flat surfaces exposed to the air but very little material to store heat. Therefore, it loses its stored heat much faster than the cube or the sphere. A sphere has the smallest surface area to volume ratio among all geometrical shapes, making it the most efficient at retaining heat and the slowest to cool. The circular plate reaches room temperature first, followed by the cube, and finally the sphere.
science-and-technology: A hollow sphere of radius R, a hollow cube of side R and a thin circular plate of radius R, made up of the same material
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