Question

Three 60 W incandescent bulbs are connected in a parallel. Now suppose that one of the bulbs is fused. What will be the total power consumed now?

Answer 1

Let the resistance of each bulb be R

Therefore the initial resistance $R_{res}=\frac{R}{3}$

Current $I_i=\frac{3V}{R}$

$P=I_i^{2}R=\frac{9V^2}{R}=60$

$\frac{V^2}{R}=\frac{20}{3}$

Now when the bulb is fused $R_{res}=\frac{R}{2}$

Current $I_f=\frac{2V}{R}$

$P_f=\frac{4V^2}{R}=\frac{80}{3}$