Derive the expression for the heat produced due to a current I flowing for a time interval t through a resistor R having a potential difference V across its ends. With which name is this relation known? b) How much heat will an instrument of 12W produce in one minute if it is connected to a battery of 12V? c) The current passing through a room heater has been halved. What will happen to the heat produced by it? d) What is meant by the heating effect of current? Give two applications of the heating effect of current. Name the material which is used for making the filaments of an electric bulb.

1. When an electric charge Q moves against the potential difference V then the amount of work done is given as: W = Q × V (1)

We know, current I = Q/T Q = IT (2)

By Ohm’s law, V/I = R

V = IR (3)

Substituting the equation (2) and (3) in (1), we get W = I2RT

Assumption:

The electrical work done is converted into heat energy Therefore, heat produced is H = I2RT

The above equation is known as Joule’s law of heating

1. Given, P = 12W V = 12V T = 60s

We know that, P =VI

I = P/V

= 12/12

= 1amp V = IR R = V/I

= 12/1

= 12 ohm H = I2RT H = 720J

1. Since the heat produced is directly proportional to the square of the current, the heat produced by the heater will becomes one-fourth.

1. The heating effect of current is the production of heat when an electric current is passed through the wire that has a high resistance. This effect is used in electric oven and electric heaters.

1. For the making of an electric bulb, tungsten is