Required Practical - I–V Characteristics
Physics: AQA GCSE Higher, topic 2.3.3
Investigating I–V Characteristics
This experiment aims to construct and use electrical circuits (based on circuit diagrams) to explore how current changes with potential difference for different components.
Apparatus
- Ammeter (for measuring current)
- Voltmeter (for measuring potential difference)
- Variable resistor (rheostat)
- Fixed resistor (100–500 Ω range)
- Filament lamp
- Diode
- DC power supply
- Connecting wires
Variables
- Independent variable:
- Potential difference (voltage, V)
- Dependent variable:
- Current (I)
- Control variables:
- Same power supply throughout the investigation
- Consistent equipment (same wires, same ammeter/voltmeter, same variable resistor)
- Maintain components at constant temperature
Method
- Assemble the circuit containing the fixed resistor as shown in the diagram.
- Gradually alter the voltage across the component by adjusting the variable resistor. Record 8–10 voltage readings across a range of values.
- For each voltage, record the current shown on the ammeter and calculate the mean current.
- Increase the potential difference in increments of 0.5 V, and repeat the process.
Method (continuation)
- Switch off the circuit between each set of readings to prevent the components and wires from overheating.
- Reverse the polarity of the power supply and repeat the measurements to obtain readings for negative voltages and currents.
- Replace the resistor with the filament lamp, and then with the diode, repeating the procedure for each.
Analysing Results
- Plot graphs of current (I) on the y-axis against voltage (V) on the x-axis.
- A straight-line graph shows an ohmic conductor (e.g. the fixed resistor), where current is directly proportional to voltage and Ohm’s Law is obeyed (V = IR).
- A curved graph indicates a non-ohmic conductor (e.g. filament lamp or diode) — these do not obey Ohm’s Law, as resistance changes with current or temperature.
- Compare your graphs to the expected I–V characteristics for each component.
Safety Precautions
- Avoid touching wires or components when the circuit is live, as they can become very hot.
- Switch off the power supply between measurements to prevent overheating.
- Keep the work area dry–no liquids should be near the electrical apparatus.
- Handle the filament lamp carefully, as it may stay hot for a while after use.
Test yourself on Required Practical - I–V Characteristics
What does a straight-line I–V graph indicate?
Which of the following components does not obey Ohm’s Law?