SUB-TOPIC :HEATING EFFECT OF CURRENT

Heating Effect of Electric current

When electric current passes through a high resistance wire, the wire becomes and produces heat. This is called heating effect of current.
This phenomenon occurs because electrical energy is gets transformed into heat energy when current flows through a wire of some resistance say R Ω.
Role of resistance in electrical circuits is similar to the role of friction in mechanics.
To we will now derive the expression of heat produced when electric current flows through a wire.
For this consider a current I flowing through a resistor of resistance R. Let V be the potential difference across it as shown in the figure 6
Let t be the time during which charge Q flows. Now when charge Q moves against the potential difference V , then the amount of work is given by
Therefore the source must supply energy equal to VQ in time t. Hence power input to the circuit by the source is
The energy supplied to the circuit by the source in time t is P×t that is, VIt. This is the amount of energy dissipated in the resistor as heat energy.
Thus for a steady current I flowing in the circuit for time t , the heat produced is given by

Applying Ohm's law to above equation we get

This is known as Joule's Law of heating
According to Joule's Law of Heating , Heat produced in a resistor is
(a) Directly proportional to the square of current for a given resistor.
(b) Directly proportional to resistance of a given resistor.
(c) Directly proportional to time for which current flows through the resistor.