Question

6. Two light bulbs are designed for use at 120 V and are rated at 75 W and 150 W. Which light bulb has the greater filament resistance? Why? ​

Answer 1

$\\ \bull\tt\longrightarrow P=\dfrac{V^2}{R}$

• P is power
• R is resistance

$\\ \bull\tt\longrightarrow R=\dfrac{V^2}{P}$

Hence

$\\ \bull\tt\longrightarrow R\propto V$

$\\ \bull\tt\longrightarrow R\propto \dfrac{1}{P}$

• Therefore if power is low then resistance will be high.

The first bulb has less power hence it has greater filament resistance.