ICSE Class 8 Answered

Convection is the transfer of heat by the movement of particles of a medium from one place to another.

It occurs only in liquids and gases.

When a substance is heated the molecules absorb heat and expand, and they become lighter than the rest of the molecules of the substance and rise upwards taking the heat energy with them.

This results in the generation of convectional currents taking the warmer molecules up and the colder molecules sink down.