Question

A student in a physics lab mistakenly wired a light bulb, battery, and switch as shown in Figure 21.44. Explain why the bulb is on when the switch is open, and off when the switch is closed. (Do not try this—it is hard on the battery!)

Short answer

The bulb is turned on when the switch is open because all current travels through it, and it is turned off when the switch is closed because no current flows through it.

Step-by-step solution

Definition of the circuit.

The term "circuit" refers to a set of electrical connections.

Circuits are closed-loop or route systems that consist of a network of electrical components through which electrons can travel.

Explaining why the bulb is on when the switch is open

Because the potential difference remains the same in parallel, more current flows through the smaller resistance and vice versa.

The bulb receives all of the currents from the battery, while the switch receives none. As a result, the bulb is turned on when the switch is turned on.

When a switch is open, it has no resistance and hence the maximum current can pass through it. As a result, all of the current from the battery passes via the switch and does not pass through the bulb. As a result, when the switch is open, the light is turned off.

Therefore, when the switch is open, the bulb is on because all current goes through it, and when the switch is closed, no current flows through it.