Collecting an I-V curve
Reverse the power supply for negative potential differences and record pairs of current and potential difference. Use a suitable scale and explain the different curve shapes for a resistor, filament lamp and diode.
GCSE Physics resources
AQA GCSE Electricity
I-V Characteristics Required Practical
Reverse the power supply for negative potential differences and record pairs of current and potential difference. Use a suitable scale and explain the different curve shapes for a resistor, filament lamp and diode.
Start here
The revision snapshot
Reverse the power supply for negative potential differences and record pairs of current and potential difference. Use a suitable scale and explain the different curve shapes for a resistor, filament lamp and diode.
By the end, you should be able to:
- Collecting an I-V curve.
- Apply the electricity model, evidence or method to an unfamiliar exam context.
- Recognise and correct this wrong turn: Only taking positive p.d. readings.
Before you revise
Diagnostic question
Choose an answer from memory. Your result tells you what to watch for in the guide.
Core revision guide
Learn the model, then use it
I-V Characteristics Required Practical questions become manageable when the central model, evidence and exam method are kept together. Read the explanation, test the misconception and then apply the idea without looking back.
Build the physics picture
Take measurements in both directions of potential difference so the graph shows the full characteristic. A fixed resistor gives a straight line, a filament lamp curves as it warms and a diode has almost no current until it is forward biased enough to conduct.
The relationship for this guide
Resistance at a point: R = V ÷ I (Ω, V, A). Choose each relationship from the physical change described, convert quantities into compatible units and keep the unit beside the final answer.
Misconception clinic
Replace the tempting answer
Read each belief, say what is wrong with it, then compare your correction.
Tempting idea: Only taking positive p.d. readings.
Use instead: Reverse the power supply for negative potential differences and record pairs of current and potential difference. Use a suitable scale and explain the different curve shapes for a resistor, filament lamp and diode.
Tempting idea: Putting the voltmeter in series.
Use instead: Take measurements in both directions of potential difference so the graph shows the full characteristic. A fixed resistor gives a straight line, a filament lamp curves as it warms and a diode has almost no current until it is forward biased enough to conduct.
Tempting idea: Calling every curved graph a diode.
Use instead: State how polarity is reversed, how readings are taken safely and how the graph demonstrates component behaviour.
Retrieval practice
Quick checks
Worked examples
See the method being built
These examples expose the difference between a secure collecting an i-v curve method and the common error “Only taking positive p.d. readings.”.
Example 1 · Full I–V method
Describe how to collect an I–V characteristic for a fixed resistor.
- Use a variable d.c. supply, ammeter in series and voltmeter in parallel.
- Take paired V and I readings in small steps.
- Reverse the supply and repeat for negative p.d.
Show the answer
Plot current against potential difference. The fixed resistor should give a straight line through the origin if its temperature is constant.
Example 2 · Identify a graph
An I–V graph has almost no current for negative p.d. and then rises sharply for positive p.d. Identify the component.
- Look for one-way conduction.
- Compare with resistor and lamp behaviour.
- Name the component.
Show the answer
It is a diode, which conducts mainly in its forward direction.
Example 3 · Explain lamp curve
Explain why the gradient of a filament lamp I–V graph falls at high p.d.
- High p.d. gives higher current.
- The filament temperature rises.
- Resistance rises, so current increases less per volt.
Show the answer
The lamp gets hotter and its resistance increases, producing a curve rather than a straight line.
Exam precision
Exam technique: Collecting an I-V curve
Do this: State how polarity is reversed, how readings are taken safely and how the graph demonstrates component behaviour.
Independent practice
Exam-style questions
Write an answer before opening the marking guidance. Then edit the exact phrase or step that would gain the next mark.
1. State the two meters used in an I–V characteristics practical.
[1 mark]Show marking guidance and model answer
Marking guidance: Award one mark for the precise statement shown in the model answer.
Model answer: An ammeter and a voltmeter.
2. Describe how the ammeter and voltmeter are connected.
[2 marks]Show marking guidance and model answer
Marking guidance: 2 marks are available for relevant, linked physics points that match the model answer.
Model answer: Ammeter in series with the component; voltmeter in parallel across it.
3. Explain why readings are taken for both positive and negative p.d.
[3 marks]Show marking guidance and model answer
Marking guidance: Award up to 3 marks for distinct physics points joined into a clear cause-and-effect chain.
Model answer: To show whether current behaves differently when the direction is reversed, especially for a diode.
4. State one way to improve resolution on an I–V graph.
[1 mark]Show marking guidance and model answer
Marking guidance: Award one mark for the precise statement shown in the model answer.
Model answer: Take smaller p.d. intervals and use a sensible large graph scale.
5. Describe the I–V graph of a filament lamp.
[2 marks]Show marking guidance and model answer
Marking guidance: 2 marks are available for relevant, linked physics points that match the model answer.
Model answer: It is a curve through the origin, becoming less steep as p.d. increases because resistance rises with temperature.
6. Explain why a fixed resistor should be allowed to cool during the investigation.
[3 marks]Show marking guidance and model answer
Marking guidance: Award up to 3 marks for distinct physics points joined into a clear cause-and-effect chain.
Model answer: Keeping temperature constant helps it remain ohmic and makes the comparison valid.
Questions pupils ask
I-V Characteristics Required Practical FAQs
What is the main idea in I-V Characteristics Required Practical?
Reverse the power supply for negative potential differences and record pairs of current and potential difference. Use a suitable scale and explain the different curve shapes for a resistor, filament lamp and diode.
What mistake should I avoid in I-V Characteristics Required Practical?
Only taking positive p.d. readings. Take measurements in both directions of potential difference so the graph shows the full characteristic. A fixed resistor gives a straight line, a filament lamp curves as it warms and a diode has almost no current until it is forward biased enough to conduct.
Useful next steps
Connect this guide to your next task
Resistance Required PracticalChange one factor such as wire length, keep material and cross-sectional area constant, measure current and potential difference, and calculate resistance for each reading. The circuit should be switched off between readings to limit heating.Current, Charge and Potential DifferenceCurrent is charge flowing per second, while potential difference is the energy transferred per coulomb. Use Q = It and V = E/Q to connect the measurements to the particle and energy models.AQA GCSE Physics Required PracticalsRequired-practical questions test whether you can connect a method to the physics. Name the variable, explain why the control matters and use data rather than vague claims.
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