Resistance of a Wire
Introduction
In this title we are going to explore how the electrical resistance of a wire depends on its length.
We are going to do this by looking at an e-scenario of a wire connected in series with a power supply and an ammeter, and in parallel with a voltmeter.
Finally, we will look at a GCSE exam question where we can apply what we have learned.
Switch on the power supply.
The supply will be already set to a voltage of 1.5V and a maximum current of two amps.
You will see an indication on the power supply’s screen that the supply is on.
Note that the ammeter and the voltmeter now give readings in Amps and Volts.
Changing the length of the wire
You can drag the crocodile clip to change the effective length of the wire in the circuit.
Below shows the circuit which makes clear how the crocodile clip determines the length of the wire in the circuit.
Showing how the length of the wire affects resistance
Start with crocodile clip at 0.1m, take readings of the voltage and current;
Change the length of the wire by moving the crocodile in steps of 0.1m up to 0.8m taking the same readings.
Complete the table shown here:
Calculate the Resistance for each step from R = V/I where V is the voltage and I is the current;
You should find the resistance is increasing as the length is increasing.
Plot a graph with the length of the wire on the X-axis, and the resistance on the Y-axis.
You should find a graph like the one shown on the right.
Exam Questions
Exam Queastion AQA May 2024 Foundation Paper 1
Note that this is worth 6 marks and lots of space has been allowed for the answer.
You should be familiar with the method as given in the previous sections, if not then repeat the instructions using the e-scenario.
Make sure you are as comprehensive as you can be. The examiner is clearly expecting a detailed answer.
This should be obvious from the graph you plotted on this slide. If it isn’t, go back to collecting the data and plotting the graph.
This should be obvious from the graph you plotted in the previous section. If it isn’t, go back to collecting the data and plotting the graph.
In this question the experiment was set up with a single battery cell, which we are now told has a potential difference of 1.5V.
Batteries like this, as shown to the right, are used in a multitude of domestic devices.
Do you consider 1.5 V is high enough to give you a significant shock?
