The effect of the length of a piece of wire on it’s resistance

Plan

Safety

In this investigation I will be using electricity to I will make sure all surfaces involved are dry as will all relevant pieces of equipment. Also, the wire may accumulate some heat so I will not touch it during the experiment.

Preliminary experiment

In this experiment I will use the circuit shown on the next page. I will try several different of wire and several voltages to see which are viable for accurate measurements.

I will try the experiment using lengths from 100cm to 10 cm and 4 volts on the power pack.

Preliminary experiment results

Length (cm)

Voltage (V)

Current (A)

Resistance (?)

00

.8

0.43

4.186046512

90

.9

0.45

4.222222222

80

.9

0.52

3.653846154

70

.9

0.53

3.58490566

60

.6

0.66

2.424242424

50

.7

0.74

2.297297297

40

.6

.15

.391304348

30

.6

.32

.212121212

20

.2

.9

0.631578947

0

0.9

2.8

0.321428571

These results are suitable to form an accurate conclusion and measurements.

Equipment

Wires, power pack, 1m of ni-chrome wire, voltmeter and an ammeter.

Method

Set up equipment as shown in the diagram for the preliminary experiment. I am using this set up because it is viable to record all the needed values. Test the wire with the power pack set to 4 volts. Record the voltage and current each time. I will do two experiments and then find an average so as to attain a more general set of results.

Prediction

I predict that the resistance will be directly proportional to the length of the wire, i.e. if the wire is 30cm long the resistance will be half that of one 60cm long. This is because all the electrons will have to squeeze through a smaller gap for a longer time in the longer wire, thus slowing it down for a longer time.

Results

Final Results

Experiment #1

Length (cm)

Voltage (V)

Current (A)

Resistance (?)

00

.9

0.42

4.523809524

90

.9

0.46

4.130434783

80

.8

0.51

3.529411765

70

.9

0.54

3.518518519

60

.7

0.65

2.615384615

50

.8

0.71

2.535211268

40

.6

.12

.428571429

30

.6

.3

.230769231

20

.3

.9

0.684210526

0

0.9

2.9

0.310344828

Experiment #2

Length (cm)

Voltage (V)

Current (A)

Resistance (?)

00

2.2

0.44

5

90

2.1

0.51

4.117647059

80

2.2

0.57

3.859649123

70

2

0.63

3.174603175

60

2

0.73

2.739726027

50

.9

0.82

2.317073171

40

.9

0.96

.979166667

30

.9

.2

.583333333

20

.8

.5

.2

0

2.4

.5

.6

Average Resistance

Length (cm)

Resistance (?)

Resistance (?) To 1 DP

00

4.7619

4.8

90

4.124

4.1

80

3.6945

3.7

70

3.347

3.3

60

2.678

2.7

50

2.426

2.4

40

.754

.8

30

.407

.4

20

0.9421

0.9

0

0.95515

Conclusion

My results more or less match my prediction in that the resistance did double as the length did. An example of this is the average resistance of 100cm was 4.8? and the average resistance for 50cm was 2.4?. This is because it takes the electrons longer to get through a long tight space than a small one, thus increasing the resistance.

Evaluation

There was only on notable anomalous result, the one for 20cm and 10cm in the second experiment. This is also reflected in the average results, but not to such a great extent. The measurements were as accurate as possible with the tools provided, and I used spreadsheets and computers to do the calculations, allowing a greater deal of accuracy.

I think that given more time we could further improve the procedure by perhaps constructing a method of keeping the wire cool. This is because resistance will increase at high temperatures. Also, the accuracy of the measurements could be improved by using a data logger, but there was not on available. As a further investigation I could enquire as to how heat, thickness and light affect resistance.

The results were sufficient to support a firm conclusion, as can be seen on the graph. The lines all follow the same trend and are very close.

By Andrew Goodbourn 10O