Question 1 (2 marks)
Method
Where are the ammeter and voltmeter connected?
Show model answer / marking points
Ammeter in series (1); voltmeter in parallel with component (1).
Required Practical 16: I-V Characteristics | AQA GCSE Science | The Science Department
About this practical and its aim
Aim
Investigate current–potential difference characteristics of a fixed resistor, filament lamp and diode.
Introduction
This is another great way to learn about circuits and how potential difference (voltage) affects the current through the wires. You need to measure how these two variables behave through resistors, filament bulbs and diodes. To ensure that any effects are due to the changes you make, temperature must remain constant. (Remember that filament bulbs produce light because they get hot, in a most homes now, filament lamps are things of the past).
The science behind the practical
An ohmic resistor at constant temperature has a linear I–V relationship. Heating changes filament-lamp resistance; a diode conducts mainly in one direction.
Key things to remember
Connect ammeter in series and voltmeter in parallel; vary p.d.; reverse polarity as appropriate for each component.
Equipment and apparatus
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D.c. supply
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ammeter
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voltmeter
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variable resistor
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fixed resistor
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filament lamp
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diode
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protective series resistor
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switch and leads
Method: How to carry out the experiment
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Collect all of the equipment needed to make up the circuit shown.
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Construct the circuit, ensure that the ammeter is in series and that the voltmeter is in parallel.
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Turn on the power supply (DC 4V) and adjust the variable resistor until the voltmeter reads 0.5V. Record the current.
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Adjust the variable resistor until the voltmeter reads 1.0V and record the new current.
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Continue until you reach 4.0V. You can then repeat all of these results so that you can spot anomalies, remove them and calculate a mean.
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Ensure that you turn off the power supply between readings as the current will generate heat in the conductors which will change the resistance.
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Plot a graph of Potential Difference (x-axis) against Resistance (y-axis). This will show if the resistor is an ohmic conductor.
Variables and fair testing
| Type of variable | What is measured or controlled? |
|---|---|
| Independent variable | Potential difference across the component |
| Dependent variable | Current through the component |
| Control variables | Component used; temperature for fixed resistor; measurement range |
Safety and managing risks
Follow your teacher's instructions and your school's risk assessment. This page is not a substitute for a formal risk assessment.
| Hazard | Risk | Precaution |
|---|---|---|
Hot filament lamp or resistor |
Burns |
Avoid touching components until cooled. |
Diode or leads overheating |
Component damage and possible burns |
Use a suitable protective resistor; check circuit before power on. |
Results, calculations and analysis
Recording, presenting and interpreting results
Record paired V and I readings and plot characteristic graphs for each component, including negative polarity where suitable.
Calculations
Resistance = potential difference ÷ current for readings where current is non-zero.
Conclusions, accuracy and evaluation
Drawing a conclusion
A fixed resistor shows a straight-line characteristic at constant temperature; a filament lamp curves; a diode is directional.
Evaluating the investigation
Use suitable current-limiting resistor with diode; switch off between readings to limit heating.
More to learn
I–V shapes
An ohmic resistor at constant temperature produces a straight line through the origin; filament lamp curves as it warms; diode is directional.
Common exam mistake
The gradient of a current (y) against voltage (x) graph is 1/R, not R.
GCSE examination practice
Answer each question in full before opening the model answer. Check your work against the marking points and look for scientific key words.
Question 2 (2 marks)
Analysis
Why does a filament lamp I–V graph curve?
Show model answer / marking points
The filament heats as current rises (1), so resistance increases (1).
Question 3 (2 marks)
Analysis
Describe the I–V characteristic of a diode.
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Very little current in reverse direction (1); current rises strongly after sufficient forward voltage (1).
Question 4 (2 marks)
Evaluation
Suggest one improvement to make the investigation more reliable and explain why it helps.
Show model answer / marking points
Repeat measurements and calculate a mean (1), reducing the influence of random variation/anomalies (1). Alternative valid improvement specific to the experiment with explanation can gain both marks.
This page was updated on: 22nd June 2026