Question

Two lamps of rating $100W$, $220V$ and $60W$ , $220V$ are joined in parallel with $220V$ line. How much current will flow through the circuit?

Answer 1

Given

$P_1=100W$ $V_1=220V$

$P_2=60W$ $V_2=220V$

We know that

$P=\frac{V^2}{R}$

So $R=\frac{V^2}{P}$

$R_1=\frac{V_1^2}{P_1}=\frac{{220}^2}{100}$=$484\Omega$

$R_2=\frac{V_2^2}{P_2}=\frac{{220}^2}{60}$=$\frac{2420}{3}\Omega$

In parallel

$\frac{1}{R}=\frac{1}{R_1}+\frac{1}{R_2}$=$\frac{1}{484}+\frac{3}{2420}=\frac{8}{2420}$

$R=302.5\Omega$

$V=IR$

Supply=$V=220V$

$220=I\times 302.5$

$I=0.727A$