Question

Two lamps, one rates $100$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.

Answer 1

Rating of first lamp is given as : $P_1=100W$ and $V_1=220V$
Thus resistance of first lamp $R_1=\frac{V_1^2}{P_1}=\frac{{220}^2}{100}=484\Omega$
Supply voltage $V_s=220V$
Current drawn by first lamp $I_1=\frac{V_s}{R_1}=\frac{220}{484}=0.45A$
Rating of second lamp is given as : $P_2=60W$ and $V_2=220V$
Thus resistance of second lamp $R_2=\frac{V_2^2}{P_2}=\frac{{220}^2}{60}=806.67\Omega$
Current drawn by second lamp $I_2=\frac{V_s}{R_2}=\frac{220}{806.67}=0.27A$