1)Conduction: Conduction is a process of heat transfer from one particle of the body to another in the direction of fall of temperature. The particles themselves remain in fixed position relative to each other. The heat transfer in a metal rod is by conduction.

2)Convection: Convection is a process of heat transfer from one particle of the body to another by convection current. In this case, the particles of the body move relative to each other. The heat transfer, in case of liquids and gases, takes place according to convection.

3)Radiation: Radiation is a process of heat transfer from a hot body to a cold body, in a straight line, without affecting the intervening medium. The heat of sun reaches to us according to radiation.

According to Stefan's law, the total radiation from a black body per second per unit area is directly proportional to the fourth power of the absolute temperature. Stefan Boltzmann law is applicable for heat transfer by radiation. The unit of Stefan-Boltzman is Watt/m²K⁴.