Question

For the circuit shown, a shorting wire of negligible resistance is added to the circuit between points $A$ and $B$. When this shorting wire is added, bulb-3 goes out. Which bulbs (all identical) in the circuit brighten?

• A. Only bulb$-2$
• B. Only bulb$-4$
• C. Only bulbs $1$ and $4$
• D. Only bulbs $2$ and $4$

Answer 1

The correct option is C Only bulbs $1$ and $4$

Shorting bulb 3 decreases the resistance in the right branch, increasing the current through bulb 4 and decreasing the total circuit resistance. This increases the total current in the main branch containing bulb 1. Hence bulbs 1 and 4 will be brighten in circuit.