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Year 10
Edexcel
Foundation

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.

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New
New
Year 10
Edexcel
Foundation

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.

Download all resources
Share activities with pupils

Lesson details

Key learning points

  1. An appropriate range of p.d. values includes 0 V and the maximum p.d. of the lamp and at least four other readings.
  2. For electricity investigations, it is good practice to take many more than the minimum number of measurements.
  3. After plotting a graph, extra readings could be taken to fill gaps or to check possible errors.
  4. Plots that lie off the best fit line are possible errors that need to be checked.
  5. 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

A simple string loop model of a series circuit can be helpful for showing: p.d. corresponds to the size of push (caused by an electric field); the amount of string passing a point each second corresponds to current; and firmness of a grip on the string corresponds to resistance.
Teacher tip

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).

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Starter quiz

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6 Questions

Q1.
What is the correct name for the electrical device shown?
An image in a quiz
an LED bulb
Correct answer: a filament bulb
a glass bulb
a fluorescent bulb
Q2.
Why is the filament glowing?
An image in a quiz
there is a chemical reaction
the filament is burning
the vapour in the bulb is glowing
Correct answer: the wire filament is heated by an electrical current
Q3.
Which of the following statements about filament bulbs is incorrect?
Correct answer: they are very energy efficient
they get very hot
they use a thin wire coil
they require an electrical current
Q4.
Which of the following statements are correct?
a voltmeter should be connected in series
Correct answer: a voltmeter should be connected in parallel
Correct answer: an ammeter should be connected in series
an ammeter should be connected in parallel
Q5.
Which of the following components is represented by the circuit symbol shown?
An image in a quiz
resistor
thermistor
Correct answer: variable resistor
fuse
heater
Q6.
Which of the following equations shows the correct relationship between potential difference, V, current, I and resistance, R?
R = I × V
R = I ÷ V
Correct answer: R = V ÷ I

Exit quiz

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6 Questions

Q1.
Match each of the following components to their function in a circuit with a cell and filament lamp.
Correct Answer:voltmeter,measures the p.d. across the lamp

measures the p.d. across the lamp

Correct Answer:ammeter,measures the current through the lamp

measures the current through the lamp

Correct Answer:variable resistor,changes the p.d. across the lamp

changes the p.d. across the lamp

Correct Answer:filament lamp,get brighter when more current flows

get brighter when more current flows

Q2.
What mistake has been made in the circuit shown in the diagram below?
An image in a quiz
only the voltmeter is incorrectly placed
only the ammmeter is incorrectly placed
Correct answer: both the voltmeter and ammeter are incorrectly placed
only the variable resistor is incorrectly placed
the voltmeter, ammeter and variable resistor are incorrectly placed
Q3.
What is 5 milliamps (mA) when converted to amps (A)?
Correct answer: 0.005 A
0.05 A
50 A
5000 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)?
0.2
1.8
3.6
Correct answer: 5.0
Q5.
What should the line of best fit look like on the graph shown?
An image in a quiz
the points should be connected with straight lines between each pair
a single straight line that doesn't pass through the origin
a single straight line that passes through the origin
Correct answer: a single curved line that passes through the origin
Q6.
Which of the following statements are correct when a filament lamp becomes brighter?
Correct answer: the current has increased
the current has decreased
Correct answer: the resistance has increased
the resistance has decreased

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