When an electric current is passed through a conductor, it becomes hot. This is called heating effect of current. The heating effect of current is obtained by the transformation of electrical energy into heat energy. A battery of a cell is a source of electrical energy. The chemical reaction within the cell generates the potential difference between its two terminals that sets the electrons in motion to make the current flow through a resistor. The source has to keep expending its energy. A part of the source energy in maintaining the current is consumed into useful work and rest of the source energy is wasted in heat.
The heat produced in a wire is directly proportional to :
(i) square of current (I2)
(ii) resistance of wire (R)
(iii) time (t), for which current is passed.
Joule's Law of heating states that when a current of ' I ' amperes flows in a wire of resistance ' R ' ohms for time ' t ' seconds, then the heat produced in the conductor is equal to the product of the square of the current, resistance of the wire and time for which current is passed. Joule's Law of heating gives the formula-
H=I2×R×t
Since, H∝R, therefore if the resistance in the circuit is doubled then heat produced will also get doubled.