First slide

Electrical power

Question

When electric bulbs of same power, but different marked voltage are connected in series across the power line, their brightness will be

Easy

A

proportional to their marked voltage
B

inversely proportional to their marked voltage
C

proportional to the square of their marked voltage
D

inversely proportional to the square of their marked voltage

Solution

Resistance of bulb $R = \frac{V^{2}}{P},$ where V is the marked voltage and P is the marked power. P is same for both. As both bulbs are connected in series, so current in both of them will be same. So, brightness $\propto R \propto V^{2} .$

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