ExpertHard6 marksExtended Response
AQA GCSE · Question 03.1 · Electricity
A student investigated how the length of a wire affects its resistance at a constant temperature. The student used a power supply, an ammeter, a voltmeter, a switch, a resistor wire attached to a ruler, and connecting leads.
Describe a method the student could have used to collect the data needed to plot a graph of resistance against the length of the wire.
A student investigated how the length of a wire affects its resistance at a constant temperature. The student used a power supply, an ammeter, a voltmeter, a switch, a resistor wire attached to a ruler, and connecting leads.
Describe a method the student could have used to collect the data needed to plot a graph of resistance against the length of the wire.
How to approach this question
This is a 6-mark question about experimental method. You need to provide a logical, step-by-step procedure.
1. Start by describing the circuit setup. Where do the ammeter and voltmeter go?
2. Explain how you will measure the independent variable (length) and the dependent variables (voltage and current).
3. State the equation needed to calculate the resistance.
4. Describe how you will get a range of results.
5. Mention any control variables (like temperature) and how you will control them.
6. Mention any steps to ensure accuracy or reliability (e.g., repeating readings).
Full Answer
To investigate the relationship between the length of a wire and its resistance, a circuit is needed to measure the potential difference (V) across the wire and the current (I) flowing through it.
- **Circuit:** The ammeter must be connected in series with the wire to measure the current flowing through it. The voltmeter must be connected in parallel across the specific length of wire being tested to measure the potential difference across it.
- **Procedure:**
1. Connect the circuit as described.
2. Attach crocodile clips to the wire to select a specific length (L), measured with a ruler.
3. Close the switch, record V and I.
4. Calculate resistance R = V/I.
5. Repeat for at least 5 different lengths, e.g., 20cm, 40cm, 60cm, 80cm, 100cm.
- **Control Variable:** The temperature of the wire must be kept constant, as resistance changes with temperature. This can be achieved by using a low current and turning off the power between readings to prevent the wire from heating up.
Common mistakes
✗ Placing the ammeter in parallel or the voltmeter in series.
✗ Forgetting to mention the calculation R = V/I.
✗ Not explaining how to get a range of results (i.e., by changing the length).
✗ Forgetting to mention control variables, especially temperature.
Practice the full AQA GCSE Physics Higher Tier Paper 1
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