Whenever electric current passed through a conductor, it becomes hot after a certain time. This effect of getting hot by conductor is called as heating effect of current; Joule’s Law.
Amount of heat produced (H) when a current I flows through a conductor of resistance R for a time t is given by
H α I2Rt …… known as joule’s law of heating.
When potential difference is applied across the conductor, E produced due to this potential exerts the force on electrons. Electrons gain kinetic energy and loss it when collide in between. This lost energy rise the temperature of the ion or atoms. Hence temperature of conductor increased.
E.m.f. of cell converts into the heat energy of conductor.