Resistance of a Wire

Length of wire – this is being investigated
Thickness of a wire – in a thin wire there are more possible paths for the electrons to pass through, therefore more electrons can flow through at one time, this increases the current which increases the resistance.

Material of wire - wires of different densities will block more or less electrons
Temperature - the vibration of warm molecules makes them more likely to collide with electrons, and resistance increases with temperature.

Variables

Independent- length

Dependent   - Voltage, current to measure, resistance

Controlled    - Temperature, material of wire, cross sectional area

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Circuit diagram

Method

1. set up apparatus as shown above
2. measure out a 1m length piece of wire and connect it to the crocodile clips
3. close the switch
4. set the variable resistor so that you get a less biased result- below 0.5 amps
5. take down results from the voltmeter (V) and the ammeter (A)
6. open the switch so that the wire doesn’t heat up
7. work out the resistance using R=V/I
8. repeat three more times
9. use a different length of wire each time as shown in the table
10. repeat each length three times

Safety

Wear safety glasses

Use very low currents below 0.5 amps because it may cause bias in results

Prediction

There will be a bigger resistance in the longer pieces of wire compared to the shorter ones which will have a smaller resistance.

In a longer wire there are more positive ions in the lattice for the electrons to collide with so there is a larger resistance. With each collision the electrons lose KE and the stationary metal ions gain KE. The electrons go slower because they have less KE so there is a smaller current.

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Strategy for results

What I will do with my results

1. Collect repeats and average
2. Calculate resistance and length
3. Put results in table
4. Put results from table into a graph

Table

 

Graph showing length of wire against resistance

Results table 

Conclusion

As the length gets bigger the resistance also gets bigger.

To get an understanding of the results a graph was plotted, it was plotted using length against resistance and a line of best fit was drawn.

The trend on the graph shows that as length is increased the resistance gets bigger, this is shown in the graph as at 20cm the resistance was 0.6Ω and at 40cm the resistance was 1.23Ω.

Scientific explanation

In a longer wire there are more positive ions in the lattice for the electrons to collide with so there is a larger resistance and in a smaller wire there are less positive ions for electrons to collide with so there is a bigger resistance. With each collision the electrons lose KE and the stationary metal ions gain KE. The electrons go slower because they have less KE so there is a smaller current and a bigger resistance.

The results support my prediction as there was a bigger resistance in the longer pieces of wire compared to the shorter ones which had a smaller resistance.

Evaluation

The evidence is reliable as I minimised the chance of the wire heating up too much as I used a switch to turn it off when I wasn’t using it. I also took repeats and an average to make sure each result was fairly the same and there weren’t any anomalies.

There were some problems in the procedure as the wire still heated up and the measurement of the wire wasn’t very accurate as there was bends and kinks in the wire.

The improvements I could make are to make sure my measuring of the wire was accurate, to use a longer length of wire and to take more averages.

I couldn’t see any anomalies in my results or on my graph.

The other variables I could investigate are thickness of a wire and material of wire.