IGCSE · 4 · practical
Electricity and magnetism · Question 10
Electricity and magnetism · Original GioPhysics question with a detailed, mark-by-mark answer guide.
- Demand
- demanding
- Marks
- 8
- Topics
- 1
- Answer
- Complete
A student investigates how the current in a filament lamp depends on the potential difference across it. She connects the lamp to a variable power supply, with an ammeter in series and a voltmeter across the lamp.
| V / V | 0.0 | 1.0 | 2.0 | 3.0 | 4.0 | 5.0 | 6.0 |
|---|---|---|---|---|---|---|---|
| I / A | 0.00 | 0.17 | 0.28 | 0.36 | 0.42 | 0.47 | 0.51 |
- (a)
State State how the ammeter and the voltmeter must each be connected in the circuit.
2 marks - (b)
Determine Determine the resistance of the lamp when the potential difference across it is 1.0 V, and again when it is 6.0 V.
3 marks - (c)
Explain Explain, in terms of the filament, why the resistance changes in the way your answers to (b) show.
3 marks
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(a)
State State how the ammeter and the voltmeter must each be connected in the circuit.
Turn the task into a measurable method: name the independent, dependent and controlled quantities; describe apparatus and repeats; then explain how the evidence will be processed and how uncertainty or safety will be managed.
- 1
the ammeter is connected in series with the lamp
- 2
the voltmeter is connected in parallel with (across) the lamp
(b)
Determine Determine the resistance of the lamp when the potential difference across it is 1.0 V, and again when it is 6.0 V.
Turn the task into a measurable method: name the independent, dependent and controlled quantities; describe apparatus and repeats; then explain how the evidence will be processed and how uncertainty or safety will be managed.
- 1
R = V / I used at both points
- 2
at 1.0 V: R = 1.0 / 0.17 = 5.9 Ω
- 3
at 6.0 V: R = 6.0 / 0.51 = 11.8 Ω (accept 12 Ω)
(c)
Explain Explain, in terms of the filament, why the resistance changes in the way your answers to (b) show.
Turn the task into a measurable method: name the independent, dependent and controlled quantities; describe apparatus and repeats; then explain how the evidence will be processed and how uncertainty or safety will be managed.
- 1
as the current increases the filament gets hotter
- 2
the metal ions in the filament vibrate with greater amplitude
- 3
so the electrons collide with them more often and the resistance increases
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