When an electric current flows through a conductor, the conductor offers some resistance for the current flow-. As a result, some electrical energy is consumed to do work for overcoming this resistance. The electrical energy consumed reappears as heat energy and the conductor becomes hot.
The heat produced in a conductor depends upon (i) the resistance R of the conductor, (ii) the amount of current l flowing through the conductor, and (iii) the time t for which electric current is flown. In this context joule derived Joule’s law of heating, according to which, the heat produced H= I²Rt
If for same current flow the resistance of the circuit is doubled then in accordance with joule’s law the amount of heat produced is also doubled.