## Many pupils predict incorrectly that two resistors in parallel will have a larger resistance than each resistor alone.

Electricity and Magnetism

Misconception

While most pupils recognise that the effective resistance of two (or more) resistors in series is their sum, many predict incorrectly that two resistors in parallel will have a larger resistance than each resistor alone.

### Diagnostic Resources

The following worksheets may help to identify whether students hold this particular misconception.

• Episode 114: Components in Series and Parallel (16-19)

Source - TAP/ Electricity / Series and parallel circuits / ...

This teaching sequence describes demonstrations, classroom activities, and discussions aimed at helping older students understand the result of combining components in series and parallel circuits.

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• Adding a Resistor in Parallel... Shifting Energy (14-16)

Source - SPT/ Ee02TL07

When the resistor is added in parallel, an extra current loop is provided and energy is shifted from the cell at a greater rate.

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• Talking and thinking circuit calculations (14-16)

Source - SPT/ Ee02TA06

This is an interactive teacher demonstration with a difference. It involves working not with apparatus, but with numbers in carrying out circuit calculations. The idea here is to make explicit to students the steps, or underlying strategy, involved in making calculations. All too often this systematic guidance is missed out and students struggle to make sense of relatively simple questions.

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## References

The following studies have documented this misconception:

• Millar, R. and Beh, K. L. () Students’ understanding of voltage in simple parallel electric circuits. International Journal of Science Education, 15 (4),

351-361.