Question

(a) What is meant by the heating effect of current? State thee factors on which the heat produced in a wire by an electric current depends.
(b) Explain why, though the heating element of an electric heater glows but its connecting cord does not glow.
(c) An electric geyser of resistance 20 Ω takes a current of 5 A. Calculate the heat produced in 2 minutes.
​(d) Name the commercial unit of electric energy. How many joules are equal to this unit?

Answer 1

(a) When an electric current flows in a circuit, it produces heat across the resistive elements of the circuit. This is called the heating effect of current. The heat produced depends on the following factors:

(i) Current flowing the circuit.
(ii) The resistance of the circuit.

(b) The heating element of the heater is made up of an alloy which has very high resistance. So, when current flows through the heating element, it becomes too hot and glows red due to the heating effect of current. But, the resistance of cord which is usually of copper or aluminium is very low, so it does not glow.

(c) The heat produced in the geyser = $I^{2}Rt$ (Where 'I' is current, 'R' is the resistance and 't' is the time for which the current flows)

In the given case, Resistance of the geyser = 20 Ω

Current flow = 5 A

Time of current flow = 2 minutes = 120 seconds

Heat produced = $(5{)}^2\times 20\times 120=60\mathrm{KJ}$

(d) Commercial unit of electric energy is 'kWh'. $1\mathrm{kWh}=3.6\times {10}^6\mathrm{J}$