Question

A wire is joined to points X and Y in the circuit diagram shown.

A diagram of a circuit with a power source on the left. Directly above the power source is a dot labeled X and then a circle with an X in it. The circuit then splits with one path straight back to the power source and the other path has 3 circles with X in them labeled 2, 3, and 4 respectively. There is a point labeled Y between circles 2 and 3.A diagram of a circuit with a power source on the left. Directly above the power source is a dot labeled X and then a circle with an X in it. After the x are 4 different circles on the circuit with Xs in them labeled 1, 2, 3, and 4 respectively. There is a point labeled Y in between circles 2 and 3. There is a branch of the circuit from X to Y.

How does the circuit change when the wire is added?

A closed circuit occurs and makes all bulbs turn off.
An open circuit occurs and makes all bulbs turn off.
A short circuit occurs and makes bulbs 3 and 4 turn off but keeps bulbs 1 and 2 lit.
A short circuit occurs and makes bulbs 1 and 2 turn off but keeps bulbs 3 and 4 lit.

Answer 1

A short circuit is created that bypasses bulbs 1 and 2, so bulbs 1 and 2 go out and bulbs 3 and 4 stay lit.

Reason: the added wire connects the node before bulb 1 (X) to the node between bulbs 2 and 3 (Y), providing a low‑resistance path around bulbs 1 and 2. Current therefore takes the wire around those bulbs and flows through bulbs 3 and 4, leaving 1 and 2 with no current.