Question

Three bulbs of $40W,60W$ and $100W$ are arranged in series across a $220V$ supply. The bulb giving maximum brightness is of

• A. 40 W
• B. 60 W
• C. 100 W
• D. all give equal brightness

Answer 1

Answer: (A)

When bulbs are connected in series, the current in each bulb remains same. As power $P=i^{2}R$, so, the bulb having maximum resistance will appear brightest.
The resistance of a bulb,
$R=\frac{V^2}{P}\propto \frac{1}{P}$ (For same $V$)
$\therefore$ The bulb of least power possesses maximum resistance.
Hence, $40W$ bulb will appear brightest when connected in series with other bulbs.