Thermal Physics - Introduction and Modes of Transfer

Thermal physics is the combined study of thermodynamics, statistical mechanics and kinetic theory. Thermodynamics is the branch of physics that describes and correlates the physical properties of macroscopic systems of matter and energy. In other words, it is concerned with heat and related thermal phenomena. In thermodynamics, we study heat in motion. The various laws of thermodynamics enable us to accurately describes processes involved in heat energy.

Modes of transfer

When the temperature of a body increases, the energy supplied to the body is being stored in the form of thermal or heat energy. In the normal process, the transmission of heat takes place from a region of higher temperature to a region of lower temperature.

There are three modes of transmission of heat:

conduction,
convection and
radiation

Conduction

It is the process in which heat is transferred from one point to another through the substance without the actual motion of the particles.

Example

When one end of a metal bar heated, the other end becomes hot after sometimes as shown in (Fig.1.1). This is due to the vibration of the molecules. The molecules at the hot end vibrate with higher amplitude and transmit the heat energy from one particle to next and so on. However the particles remain in their mean position of equilibrium.

Fig 1.1 Process of conduction

This mode of transmission is possible in the case of solids, liquids and gas.

Convection

It is the process in which heat is transmitted from one place to another by the actual motion of the heated particles.

Example

Let us consider a breaker of water heated by a flame as shown in (Fig. 1.2).

Fig 1.2 Process of convection

The water in the central portion at the bottom of beaker gets heated first. It rises up and the water from the top comes down along the sides to get heated. This upward and downward motion can be made visible by placing a crystal of potassium permanganate at the bottom of the beaker.

Radiation

It is the process in which heat is transmitted from one place to the other directly, without the agency of any material medium.

Fig. 1.3 Process of radiation

Example

Heat from the sun reaches us with an enormous velocity of light as shown in (Fig. 1.3). Through the sun is millions of miles away from the earth and there is no material medium for the greater part of the distance, the heat reaches us with the velocity of light. Thus heat radiations can pass through vacuum. The properties of heat radiations are similar to light radiation.

Read More Topics

Linear flow of heat along a bar

Heat flow through a compound media or wall

De-Broglie’s concept of matter