Concepts of Physics

IIT JEE Physics (1978-2018: 41 Years) Topic-wise Complete Solutions

The Concept of Latent Heat

Objective

To get familiarized with the concept of latent heat.

Introduction

Latent heat is the quantity of heat absorbed by unit mass of a substance, at constant temperature, during its change of state (solid to liquid or liquid to gas).

Apparatus

spirit or alcohol

Procedure

Rub a little spirit/alcohol on your skin, you feel cool and alcohol evaporates quickly.

Discussion

When spirit is applied to your skin, the state of the spirit gets changed from the liquid to gaseous. The heat for this change of state is supplied by your hand. The heat from the hand raises temperature of the spirit upto its boiling point. At the boiling point, liquid is converted into the gaseous state. During this change of state, the substance continues to absorb heat, but its temperature remains constant. This principle is also responsible for cooling of water kept in earthen pot.

Also, we feel cool under a fan, when we are perspiring because circulating air due to fan evaporates the water better. The latent heat of vaporization is supplied by your body and you feel cool.