# Measuring the resistance of a filament lamp

I can find the resistance of a filament lamp by measuring the current and p.d. for a suitable range of p.d.

# Measuring the resistance of a filament lamp

I can find the resistance of a filament lamp by measuring the current and p.d. for a suitable range of p.d.

## Lesson details

### Key learning points

- An appropriate range of p.d. values includes 0 V and the maximum p.d. of the lamp and at least four other readings.
- For electricity investigations, it is good practice to take many more than the minimum number of measurements.
- After plotting a graph, extra readings could be taken to fill gaps or to check possible errors.
- Plots that lie off the best fit line are possible errors that need to be checked.
- The resistance of a filament lamp is calculated from an I–V graph using pairs of readings and the equation R = V ÷ I.

### Common misconception

The terms current, voltage, resistance, energy and power, together with the properties of each, are often mixed up.

As each term is introduced during this lesson, spend a few moments checking pupils’ understanding.

### Keywords

Filament lamp - a type of lamp that uses a hot wire to emit light

Variable resistor - a resistor that can be easily changed to any value in its range

Range - the minimum to maximum possible values in an experiment

Repeat reading - when a measurement is taken again to improve the experiment

Best fit line - a line that shows the underlying trend of a set of results on a graph, it can be straight or curved

### Equipment

Power supply (or battery pack), filament lamp, variable resistor, electrical leads, ammeter and voltmeter.

### Content guidance

- Risk assessment required - equipment

### Supervision

Adult supervision required

### Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

## Video

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## Starter quiz

### 6 Questions

## Exit quiz

### 6 Questions

measures the p.d. across the lamp

measures the current through the lamp

changes the p.d. across the lamp

get brighter when more current flows