Question

Calculate the resistance of 110-V light bulbs rated at 25, 60, 75 and 100W.

Answer 1

Gives

V=110V

$$P_1=25\Omega,P_2=60\Omega,P_3=75\Omega,P_4=100\Omega$$

We know that

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

$R_1=\frac{V^2}{P_1}=\frac{110^2}{25}=484\Omega$

$R_2=\frac{V^2}{P_2}=\frac{110^2}{60}=201\Omega$

$R_3=\frac{V^2}{P_3}=\frac{110^2}{75}=161\Omega$

$R_4=\frac{V^2}{P_4}=\frac{110^2}{100}=121\Omega$