3.2.4Movement and Interactions
Required Practical 15: I–V Characteristics — AQA GCSE Combined Science Synergy 8465 - Physical Sciences Revision Notes & Topical Questions
5 min read 6 parts Lesson 21 of 59
Part 1 of 4Equipment and circuit
Components
- Components A power supply (or cell), variable resistor, ammeter, voltmeter, switch, connecting leads and the test component.
- Test components are a fixed resistor, a filament lamp and a diode in turn.
Connections
- Connections The ammeter goes in series with the component.
- The voltmeter goes in parallel across only the component.
Variables
- Variables Independent: potential difference across the component. Dependent: current through it.
- Controltemperature as far as possible, the same circuit, and the supply of voltage.
Part 2 of 4Method
1
Build the circuit with the resistor as the test component, with the variable resistor in series with the supply.
2
Close the switch and adjust the variable resistor until the voltmeter shows the first value, for example 0.5 V.
3
Read and record the ammeter current.
4
Increase the potential difference in equal steps and record the current each time.
5
Swap the supply terminals (reverse the connections) and repeat to obtain negative values.
6
Repeat the whole procedure for the filament lamp, and then for the diode.
Part 3 of 4Safety and accuracy
| Issue | What to do |
|---|---|
| Wires and lamp getting hot | Switch off between readings and allow components to cool |
| Diode damage | Use a protective resistor in series with the diode so current stays low |
| Zero errors | Check meters read zero before starting |
| Reliability | Repeat readings and calculate a mean, then plot a smooth curve |
Part 4 of 4Expected results
I–V graphs
Resistor
- Resistor A straight line through the origin; the gradient of I against V is 1 ÷ R.
Filament lamp
- Filament lamp An S-shaped curve through the origin, getting flatter at higher potential differences as the filament heats up.
Diode
- Diode Flat at zero current in reverse, then current rises steeply once the forward voltage exceeds about 0.6 V.
Key terms
| Term | Meaning |
|---|---|
| Variable resistor | A resistor whose resistance can be changed to vary the current and potential difference. |
| Characteristic | A graph showing how the current through a component depends on the potential difference across it. |
| Series | Connected one after another so the same current passes through each. |
| Parallel | Connected across a component so it experiences the same potential difference. |
| Zero error | A reading shown by an instrument when the true value is zero. |
Avoid these mistakes
1
Placing the voltmeter across the whole circuit instead of only the test component.
2
Leaving the current on between readings so the wire heats and resistance changes for the resistor test.
3
Joining the points dot to dot with a ruler on the lamp graph rather than drawing a smooth curve.
4
Forgetting that a diode needs a protective resistor in the circuit.
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