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 quick 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…
- Explain collecting an i-v curve using precise physics language.
- Apply the relevant equations, diagrams or practical method to an exam-style situation.
- Use the mini quizzes and practice answers to identify and correct a misconception.
Core learning content
Learn the idea before you practise it
Start with this short teaching sequence for I-V Characteristics Required Practical. Read the model, use the visual, then test your recall before moving into examples and exam practice.
Build the 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.
Use the right relationship
Choose a relationship because of the physical change in the question, not because it is familiar. Charge and current: Q = It (C, A, s). Potential difference: V = E ÷ Q (V, J, C). Resistance: V = IR (V, A, Ω). Keep the unit next to each value while you substitute.
What a strong answer does
State how polarity is reversed, how readings are taken safely and how the graph demonstrates component behaviour. Before writing, underline the command word and identify the information that matters. Keep a calculation as equation, substitution and answer with unit; keep an explanation as a linked chain using because, so or therefore. Finish by checking that the final sentence answers the exact context in the question and that the number, direction or conclusion agrees with the evidence given.
Retrieval practice
Quick checks
Answer without looking back first. The feedback explains the model, so a wrong answer still helps you learn.
Mini quiz 1
Check the core idea
Mini quiz 2
Apply the model
Mini quiz 3
Use exam precision
Try it
I-V characteristics comparer
How do the shapes of I-V curves distinguish a resistor, lamp and diode?
What to notice: the readout and written explanation remain available if you do not use the controls.
Worked examples
See the method being built
Cover the answer, attempt the method and then compare your physics language as well as the number.
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.
Misconception clinic
Common wrong turns
Each of these is tempting because it sounds almost right. Replace it with the precise physics before you meet it in a question.
- Only taking positive p.d. readings.
- Putting the voltmeter in series.
- Calling every curved graph a diode.
Independent practice
Exam-style questions
Use the working space first. Reveal the guidance only after you have committed to an answer, then improve the exact part that would gain the next mark.
1. State the two meters used in an I–V characteristics practical.
[1 mark]Show answer and marking guidance
An ammeter and a voltmeter.
2. Describe how the ammeter and voltmeter are connected.
[2 marks]Show answer and marking guidance
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 answer and marking guidance
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 answer and marking guidance
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 answer and marking guidance
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 answer and marking guidance
Keeping temperature constant helps it remain ohmic and makes the comparison valid.
Questions pupils ask
GCSE Physics FAQs
What is the key idea in I-V Characteristics Required Practical?
Electricity questions reward careful definitions and circuit rules. Keep current, charge, potential difference, resistance, power and energy as separate quantities.
How should I practise I-V Characteristics Required Practical?
Read the snapshot, attempt the worked examples without looking, complete the mini quizzes and then use the practice questions to check your wording and method.
Next step
Keep your revision moving
Physics sticks when you move between explanation, retrieval and application.