1. Conduction: It is a process of transmission of heat in solids, without the actual movement of the particles.
Eg: When metal rod is heated at one end, after some time another end also becomes hot.
2. Convection: It is a process of transmission of heat in fluids (liquids and gases) with the actual movement of particles.
Eg: Smoke carries heat energy from the flame by convection.
3. Radiation: It is a process of transmission of heat without any medium in the form an electromagnetic waves.
Eg: Heat from the sun reaches the earth by radiation.
Wein’s displacement law: The wavelength (λm) Corresponding to maximum energy emitted by a black body is inversely proportional to its absolute temperature. i.e. λm ∝\(\frac{1}{T}\) or λm T = b. where b is a constant, called Wein’s constant. The radiation emitted by a black body is called black body radiation. The distribution of energy of a black body radiation at different temperatures is as shown in the figure.
The energy distribution is not uniform. There is a particular wavelength λm at which the energy emitted is maximum. The wavelength λm for which the intensity is maximum decreases with increase in temperature.
