Electrical Circuit
Electricity and Magnetism

Voltage in series circuits

Physics Narrative for 11-14 Supporting Physics Teaching

Voltage in series circuits: what happens?

How do the ideas about voltage work with a circuit where there is more than one bulb? In this circuit, two identical bulbs are connected in series to a 3 volt battery and a voltmeter is connected across each bulb.

What happens in the circuit?

We have already seen that adding a bulb in series results in the current being reduced (due to the increased resistance) and both bulbs becoming dim.

What happens to the voltage across each bulb?

When the second bulb is added, the same voltage appears across the two bulbs. Both are identical, what else could it be as the situation is symmetrical?

Each voltmeter reads 1.5 volt.

The rope loop provides a good teaching model to reason with.

Voltage across components in series: a summary

The sum of the voltages across the bulbs/resistors must equal the battery voltage. This follows from the energy description.

The powerin must be equal to the powerout.

The energy shifted from the chemical store of the battery must equal the energy shifted by the charged particles as they pass through the bulbs/resistors.

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