Required practical - Investigating I-V characteristics (AQA GCSE Physics Combined Science): Revision Notes
Required practical - Investigating I-V characteristics
What is this practical about?
This practical helps you understand how current and potential difference (voltage) are related in different electrical components. You'll create I-V graphs for three important components: a resistor, a filament lamp, and a diode.
An I-V characteristic is simply a graph that shows how the current flowing through a component changes when you change the voltage across it. Different components behave differently, which creates different shaped graphs.
Understanding I-V Characteristics
An I-V characteristic is a fundamental way to understand how electrical components behave. The shape of these graphs tells us important information about the component's properties and how it will perform in different circuits.
Aim of the experiment
Main Objective
Your goal is to investigate and compare the I-V graphs for:
- A resistor (fixed resistance)
- A filament lamp (resistance changes with temperature)
- A diode (only allows current in one direction)
Equipment you need
- Ammeter (to measure current)
- Voltmeter (to measure potential difference)
- Component holders
- Filament lamp
- Resistor
- Diode with protective resistor
- Variable resistor (to change the voltage)
- Switch
- Connecting leads
- Battery or power supply
Method - step by step
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Build the circuit as shown in the diagram. The ammeter goes in series (same path as current). The voltmeter goes in parallel (across the component you're testing).
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Start with one component (like the resistor) in the circuit.
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Close the switch and use the variable resistor to change the potential difference across the component.
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Record both readings - the current from the ammeter and the potential difference from the voltmeter.
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Take several measurements by adjusting the variable resistor to get different voltage values.
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Reverse the battery connections to get negative values for both current and potential difference. This gives you a complete picture of how the component behaves.
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Repeat the whole process for each of the three components.
Circuit Setup Critical Points
- Ammeter must be in series with the component
- Voltmeter must be in parallel across the component
- Always include a switch to control current flow
- Double-check all connections before closing the switch
Recording your results
Create a table for each component with two columns:
- Potential difference (V)
- Current (I)
Record both positive and negative values. For example, your readings might look like:
- When V = 1.0V, I = 0.16A
- When V = -1.0V, I = -0.15A
- When V = 0V, I = 0A
After collecting all your data, plot a graph with:
- Current (I) on the y-axis (vertical)
- Potential difference (V) on the x-axis (horizontal)
Sample Results Table
| Potential Difference (V) | Current (A) |
|---|---|
| -2.0 | -0.33 |
| -1.0 | -0.16 |
| 0.0 | 0.00 |
| 1.0 | 0.15 |
| 2.0 | 0.31 |
Remember to include both positive and negative readings for a complete I-V characteristic.
Understanding the different I-V graphs
Each component will give you a different shaped graph:
- Resistor: Straight line through the origin (ohmic behaviour)
- Filament lamp: Curved line (resistance increases as it heats up)
- Diode: Current only flows in one direction, creating a distinctive shape
The shape of each graph tells you important information about how that component behaves in a circuit.
Graph Analysis
The different shapes reveal the physics of each component:
- Straight lines indicate constant resistance
- Curved lines show variable resistance
- Asymmetrical shapes reveal directional properties
Safety considerations
Essential Safety Information
Be very careful when working with electrical circuits. Electric current can produce heat and cause burns if the current gets too high.
Always include a switch in your circuit. This lets you control when current flows and prevents the current from getting dangerously large.
Tips for getting accurate results
Improving Your Data Quality
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Don't let the current get too large. High currents cause components to heat up, which changes their resistance and affects your readings.
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Take repeat readings and calculate averages to improve reliability.
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Check your connections are secure before taking measurements.
Remember the difference between accurate and precise data:
- Accurate data: Close to the true value
- Precise data: Repeat readings are close to each other
- The best data is both accurate and precise
Key Points to Remember
- I-V graphs show current (y-axis) against potential difference (x-axis)
- Different components create different shaped graphs due to their properties
- Reverse the battery to get negative readings for a complete picture
- Safety first - use switches and avoid high currents
- Take multiple readings and calculate averages for better accuracy