Topics to revise
Circuit electricity P1
Respiration P1
Required practical - Resistance of a wire
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Resistance of a wire
Use circuit diagrams to investigate factors affecting resistance, including length of wire and series/parallel combinations
Check your understanding with these quick common questions. Use the drop down boxes to see the correct answers.
Resistance of a wire
Current, Potential difference and Resistance are linked. Resistance is just how hard it is for electrons to move around a circuit, even through wires. Different thicknesses of wire, lengths, material, all impact resistance. You can calculate resistance using V = I R (or Potential difference = Current x Resistance). Remember, Potential difference and voltage mean the same thing.
Independent variable: Wire length (or sometimes type of material, thickness).
Dependent variable: Resistance (this needs to be calculated from V and I).
Control variables : Wire thickness/material; temperature of the wire; supply voltage.
Ammeter
Voltmeter
Variable resistor
Accuracy can be improved by using a narrower crocodile clip so you can measure the length of the wire exactly. Digital ammeters and voltmeters have a higher resolution than analogue ones.
Validity can be improved by: A variable resistor can be used to adjust the potential difference. The wire can quickly overheat if left on and this increases resistance. The circuit should be switched off quickly after taking measurements.
Describe: Increasing wire length → increases resistance
Explain: Longer wires mean more collisions for electrons so resistance increases
Set up a circuit with power supply
Add an ammeter in series
Add a voltmeter in parallel.
Measure Voltage and Current for different wire lengths
Change the length by moving the crocodile clips
Allow cooling between trials.
Repeat each length 3 times and calculate a mean
Use V= IR and rearrange to Resistance = Voltage / Current to calculate resistance.