Question

A $25W$ and $100W$ bulb are joined in series and connected to the mains. Which bulb will glow brighter?

• A. $25W$ bulb
• B. $100W$ bulb
• C. Both bulb will glow brighter
• D. None will glow brighter

Answer 1

Answer: (A)

As we know that,
$P=\frac{V^2}{R}$
$\Rightarrow R=\frac{V^2}{P}$
$\Rightarrow R\propto \frac{1}{P}$
Hence, the resistance of $25W$ bulb is greater than the resistance of $100W$ bulb
Now, both the bulb are joined in series so the current will be same
So, heat produced by the bulbs
$H=i^{2}Rt$
$\Rightarrow H\propto R$
So, the heat produced by the $25W$ bulb is greater than the bulb of $100W$, because its resistance is more than that of $100W$ bulb
Hence, $25W$ bulb will glow brighter