Question

Four 60 W, 230 V bulbs are connected between the phase and the neutral as shown in the diagram. Line voltage is 230 V.

Which bulb/bulbs will glow at 60 W power?

• A. $B_1$
• B. $B_2$
• C. $B_3$
• D. $B_4$

Answer 1

Answer: (A), (B)

The correct options are
A

$B_1$

B

$B_2$

When the bulbs are connected in series, the total voltage applied is distributed across the bulbs according to their resistance whereas when the bulbs are connected in parallel the voltage across the bulb is equal to the applied voltage. Since $B_1$ and $B_2$ are in parallel and have their ends connected with the positive and negative terminal, hence they glow at 60 W. Also, $B_3$ and $B_4$ are connected in series, hence voltage across them is less than the applied voltage and therefore glow at less than 60 W.