← Series circuits

One break stops the whole series circuit

In brief

Here are the two states from the video, kept as one card: the same loop with the switch closed, then open.

6 VA0.3 AA1bulb 1bulb 2closed
Switch closed: the loop is complete, the ammeter reads 0.3 A, and both bulbs glow.
6 VA0 AA1bulb 1bulb 2open
Switch open: the loop is broken, the ammeter reads 0 A, and both bulbs are dark, though the switch touches neither of them.
Current flows only around one complete, unbroken conducting loop. A series circuit has only the one loop, so a gap anywhere makes the current zero everywhere, and every component stops.

A broken component does the same job as an open switch. When a bulb's filament snaps, the snap is a gap in the loop.

Keep this apart from the last lesson's move. There, a component was taken out and the loop was reconnected, so the smaller total resistance carried a bigger current. Here the gap stays open, and a broken loop carries no current at all.

A series loop runs a heater and a fan motor. The heater's element snaps. What happens to the fan motor?

Write down the fact:

current flows only around one complete, unbroken conducting loop

Apply it:

The snapped element is a gap, and the series circuit's one loop is broken.

So the current everywhere is zero.

The fan motor stops.

Check what you know

A series loop holds a buzzer and a bulb. The bulb's filament snaps. What does the buzzer do?

Omar says opening the switch turns off both bulbs in a series loop, even though the switch touches neither bulb. Is Omar correct?

One component in a series loop breaks. What is the current through the other components?

A motor, a buzzer, and a bulb share one series loop. The motor burns out. Which of the other components keep working?

A series circuit carries 0.4 A. One of its bulbs burns out. What is the current through the remaining components?

When one component in a series circuit breaks, every other component stops. Which statement explains why?