Given below are the four cases in which certain heat transfer is taking place : 1. Ice is melting in a glass full of water 2. Water is boiling in an open container 3. A metal rod is heated in a furnace 4. A cup of coffee is allowed to cool on a table In which of the above cases, the Newton's Law of Cooling is applicable ?

Newton's Law of Cooling states that the rate of heat loss of a body is directly proportional to the difference in the temperatures between the body and its surroundings, provided the temperature difference is small.

• Case 4 (Coffee cooling): This is a classic application where a hot liquid loses heat to the cooler ambient air through convection and radiation, following the law.
• Cases 1 and 2 (Melting and Boiling): These involve phase changes. During phase transitions, the temperature remains constant despite heat transfer (latent heat), so Newton's Law of Cooling, which depends on a temperature gradient, does not apply.
• Case 3 (Heating in a furnace): This involves heating rather than cooling. Furthermore, at high furnace temperatures, heat transfer is dominated by radiation (Stefan-Boltzmann Law) rather than the linear approximation of Newton's Law.

Therefore, the law is only applicable to Case 4.