(a) Write Joule's law of heating.(b) Two lamps, one rated 100 W; 220 V, and the other 60 W; 220 V, are connected in parallel to electric mains supply. Find the current drawn by two bulbs from the line, if the supply voltage is 220 V.

(a) Joule's Law of Heating refers to the heat generated by an electrical conductor is directly proportional to the product of its resistance $(R)$ and the square of the electric current passing through the conductor with time.

Mathematical expression for Joule's law of heating is:

$H=I^2Rt$

Where,

$H$ = Heating effect.

$I$ =  Current flowing through the conductor.

$R$ = Amount of electric resistance in the conductor.

$t$ = Time taken.

(b) Given:

Potential difference, $V$ = 220 V

 Power of 1st lamp, $P_1$ = 100 W

 Power of 2nd lamp, $P_2$ = 60 W

To find: Current drawn by the two bulbs, $(I)$.

Solution:

We know that formula of power is given as-

$P=V\times I$

$\therefore I=\frac {P}{V}$

Current drawn by 1st lamp is-

$I_1=\frac {P_1}{V}=\frac {100}{220}=\frac {10}{22}=\frac {5}{11}A$

Current drawn by 1st lamp is-

$I_2=\frac {P_2}{V}=\frac {60}{220}=\frac {6}{22}=\frac {3}{11}A$

Net current-

$I=I_1+I_2$

$I=\frac {5}{11}+\frac {3}{22}$

$I=\frac {5+3}{11}$

$I=\frac {8}{11}$

$I=0.73A$

Net current through the circuit is 0.73A.