According to Joules heating effect heat produces in a resistor is  

a) Directly proportional to square of current for the given resistor. 

b) Directly proportional to resistance for a given current, 

c) Directly proportional to the time of current flowing through the resistor. 

This can be expressed as

H = I²Rt

H is heating effect, I is electric current, R is resistance and t is time

Experiment to demonstrate Joules law of heating 

• Take a water heating immersion rod and connect to a socket which is connected to regulator. 
• It Is important to recall that a regulator controls the amount of current flowing through a device.
• Keep the pointer of regulator on minimum and count the time taken by immersion rod to heat a certain amount of water.
• Increase the pointer of regulator to next level. 
• Count the time taken by immersion rod to heat the same amount of water.
• Repeat above step for higher levels on regulator to count the time.

Observation: 

• It is seen that with increased amount of electric current, less time is required o heat the same amount of water. 
• This shows Joule's Law of Heating.

Application: 

Electric toaster, oven, electric kettle and electric heater etc. work on the basis of leafing effect of current.