Bulb Glows Only in (a) Closed Circuit (b) Open Circuit (c) in Both Circuits (d) Open Circuit if Bulb is not Fused

Answer: (a) Closed Circuit.

The bulb lights in a complete circuit because current is flowing. To glow, a bulb requires adequate current flow.

When the current passes through the bulb, the filament heats up and glows, emitting heat and light.

If the loop is open, however, the electricity cannot flow through it, and the lightbulb will stop burning.

When the key or switch is in its off position, the circuit is considered closed, and this indicates that current is flowing through the circuit (or, on).

In contrast, when a circuit is open, it indicates that there is no flow of current within the circuit because the key or switch is in the open position (or, off).

As a result, the lightbulb will shine after the circuit has been completed.