← Series circuits

Add a series component, and the current falls

In brief

Here are the video's two circuits, kept as one pair of cards.

6 VA0.75 AA1bulb 1bulb 2
Two matching bulbs on a 6 V battery: the ammeter reads 0.75 A.
6 VA0.5 AA1bulb 1bulb 2bulb 3
A third matching bulb wired into the same loop, source unchanged: the ammeter reads 0.5 A, and all three bulbs glow equally dim.
current (A)0.75 Acurrent with two bulbs0.5 Acurrent with three bulbs
Same 6 V source: more series bulbs, less current.
Adding a component in series, with the source unchanged, reduces the current everywhere in the loop. The new component's opposition stacks onto the one path, so the total resistance rises, and more resistance at the same voltage means less current.

The move also runs backward. Take a component out and reconnect the loop without it: the total resistance falls, so the current everywhere rises. A gap left open instead is a different story, and the next lesson tells it.

A series circuit holds a motor and a buzzer. A heater is added in series, and the source voltage is unchanged. What happens to the current through the motor?

Write down what changed:

a third component now sits on the loop's one path

So the total resistance rises.

The source voltage is unchanged.

More resistance at the same voltage means less current.

The current through the motor falls.

Check what you know

A resistor is added in series to a one-bulb circuit, source unchanged. What happens to the current?

Adding a series component with the source unchanged reduces the current. Why?

Tess says the battery always supplies the same current, so adding a series bulb leaves every bulb as bright as before. Is Tess correct?

Two identical bulbs glow in a series loop. A third identical bulb is wired into the loop, source unchanged. What happens to the brightness?

A buzzer sounds in a series circuit. A resistor is then added in series, source unchanged, and the buzzer gets quieter. Which statement explains why?

A series loop holds three bulbs. One bulb is taken out, and the loop is reconnected without it, source unchanged. What happens to the current?