Question

Discuss various modes of heat transfer.

Answer 1

There are three modes of heat transfer: Conduction, Convection and Radiation.

Conduction: Conduction is the process of direct transfer of heat through matter due to temperature differences. When two objects are in direct contact with one another, heat will be transferred from the hotter object to the colder one. The objects which allow heat to travel easily through them are called conductors.

Convection: Convection is the process in which heat transfer is by the actual movement of molecules in fluids such as liquids and gases. In convection, molecules move freely from one place to another.

Boiling water in a cooking pot is an example of convection. Water at the bottom of the pot receives more heat. Due to heating, the water expands and the density of water decreases at the bottom. Due to this decrease in density, molecules rise to the top. At the same time, the molecules at the top receive less heat and become denser, and come to the bottom of the pot. This process goes on continuously. The back and forth movement of molecules is called a convection current.

To keep the room warm, we use a room heater. The air molecules near the heater will heat up and expand. As they expand, the density of air molecules will decrease and rise up while the higher density cold air will come down. This circulation of air molecules is called a convection current.

Radiation: When we keep our hands near the hot stove we feel the heat even though our hands are not touching the hot stove. Here heat transferred from the hot stove to our hands is in the form of radiation. We receive energy from the sun in the form of radiation. These radiations travel through a vacuum and reach the Earth. It is the peculiar character of radiation that requires no medium to transfer energy from one object to another. The conduction or convection requires a medium to transfer the heat.

Radiation is a form of energy transfer from one body to another by electromagnetic waves.

Example:

1. Solar energy from the Sun.
2. Radiation from a hot stove.