Question

To do an experimental verification of Newton’s law of cooling, we need to take the ‘temperature’ vs ‘time’ readings, of a hot body, kept in given surroundings. An appropriate choice, of the ‘hot body’ and the ‘surroundings’, would then be: 

(1) [A hot metal sphere]; and [a ‘closed enclosure’].

(2) [A hot metal sphere]; [a stone plate to hold the sphere and kept in an uncovered enclosure]. 

(3) [An uncovered calorimeter containing hot water that is constantly being stirred]; [a slab on an open window or a table under a fan].

(4) [A fully covered calorimeter containing hot water]; [a corner of the room away from any open window or a fan].

Answer 1

Correct option: (3)

Explanation: 

Newton’s law of cooling holds for the cooling of a hot body, primarily by convection. It can then be valid even for quite a large difference of temperature between the hot body and the surroundings. 

The ‘set–up’, suggested in option (3), is most likely to ensure that the whole of the hot body cools primarily by convection. Hence it is the appropriate choice for verifying Newton’s law of cooling.