joule's law of heating: 

The heat produced in a resistor is directly proportional to the square of current
for a given resistance, directly proportional to resistance for a given current, and  the time for which the current flows through the resistor. This law is called the joule's law of heating. 

Joule's law heating is denoted by "H"

H = I²Rt

Establishment of this law in formulla: 

Let us suppose that current (I) is flowing through a resistor of resistance
(R) for the time (t). The potential difference across the resistance is (V).

The law stated that the heat produced in a resistor is :

(i) Directly proportional to the square of current (I) for a given resistance.

(ii) Directly proportional to resistance (R) for a given current.

(iii) Directly proportional to the time for which the current flows through the resistor.