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.
- Year 10
- AQA
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.
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
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.
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
Lesson video
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Prior knowledge starter quiz
6 Questions
Q1.What is the correct name for the electrical device shown?
Q2.Why is the filament glowing?
Q3.Which of the following statements about filament bulbs is incorrect?
Q4.Which of the following statements are correct?
Q5.Which of the following components is represented by the circuit symbol shown?
Q6.Which of the following equations shows the correct relationship between potential difference, V, current, I and resistance, R?
Assessment exit quiz
6 Questions
Q1.Match each of the following components to their function in a circuit with a cell and filament lamp.
Q2.What mistake has been made in the circuit shown in the diagram below?
Q3.What is 5 milliamps (mA) when converted to amps (A)?
Q4.A current of 0.6 A flows through a filament lamp when a p.d. of 3.0 V is applied across it. What is the resistance of the lamp in ohms (Ω)?
Q5.What should the line of best fit look like on the graph shown?
