Question

Study the circuit diagram.

How many bulbs will light up when switches $A$ and $B$ are closed in different situations?
A) Only switch $A$ is closed B) Only switch $B$ is closed, respectively

• A. $4,2$
  
• B. $4,3$
  
• C. $0,3$
  
• D. $0,2$
  

Answer 1

Answer: (C)

$0,3$

When only switch A is closed, the circuit is open at 'B', hence the entire circuit would be open.
Zero bulbs would glow.
If only B is closed, only the first part of the three parallel bulb circuits would be open.
Hence 3 bulbs would glow (the one in series, and the two that are part of the closed circuit).
Hence option C is correct.