Final answer:
When the switch is open, the bulb is off because the circuit is incomplete. When the switch is closed, the bulb is also off because the current flows through the switch instead.
Step-by-step explanation:
The bulb is on when the switch is open because the circuit is incomplete.
When the switch is closed, the bulb is off because the circuit is complete and the current flows through the switch rather than the bulb.
This can be explained using the concept of an open and closed circuit. An open circuit is a circuit that has a gap or break in the flow of current, preventing it from completing the loop. In this case, when the switch is open, there is a gap in the circuit and the current cannot flow through the bulb, resulting in the bulb being off.
On the other hand, when the switch is closed, it completes the circuit and provides a path for the current to flow. However, the switch itself acts as a conductor, allowing the current to bypass the bulb and flow through the switch instead. As a result, the bulb remains off.