A 25W and 100W bulbs are joined in series are connected . . .

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

Doubt by Zoya

Solution :

The brightness of bulbs depends on the intensity of heat produced in the filament.

We know,
P=V²/R

When the two bulbs are individually connected across the same voltage then the resistance of the bulbs will be given by

R=V²/P
R∝1/P — (1)

Also,
H = I²Rt

Since both the bulbs are connected in series so that same current will pass through each of them for same amount of time.

H∝R — (2)

Using equation (1) and (2)
H∝R∝1/P

H∝1/P

More heat will be produced in a bulb of low power.

So, 25 W bulb will grow brighter.

12 | LETXY