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Heating Effect of Electric Current

Generally a battery or cell is used as a source of electrical energy. A potential difference can be developed due to chemical reaction in a cell to set the electrons in motion. so that current will be constituted through a resistor or a group of resistors, which are connected to the battery or cell. For continuous drawing of current, the source has to keep expending its energy.
A part of the energy from the source can be converted into useful work and the rest will be converted into heat energy. If an electric circuit is purely resistive (only resistors are connected to a battery), the energy from the source continually gets dissipated totally in the form of heat. This effect is called as heating effect of electric current and it is effectively utilized in heater, electric iron, electric toaster, etc.
Let us assume a current I flowing through the resistor of resistance R and let V be the potential difference across the resistor. Let t be the time during which charge Q flows across.
Then, Work done (W) moving the charge (Q) through a potential difference (V) is (W) = VQ
Hence Power given to the circuit in time t is given by (P) = = VI
Energy supplied to the circuit by the source in time t = P × t = VIT
This energy (VIT) is dissipated in the resistor as heat. Thus for a steady current I, the amount of heat H produced in time t is
H =
From the Ohm’s law V = IR
H = I2Rt

The above equation is called as Joule’s law of heating.

The heat generated in a resistor is directly proportional to
  1. the square of the current for a given resistance
  2. the resistance for the given current and
  3. the time for which the current flows through the resistor.

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