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# The effect on resistance when a length of wire is changed

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Introduction

## Physics Coursework

Investigating the effect on resistance when a length of wire is changed

By Yasmin Alobaidi

Preliminary Investigation

Method

Firstly, I will investigate the effect on resistance when the length of wire is changed using a power-pack setting of 2V, 4V and 6V. I will compare the results to see which setting is the most suitable. I will choose three wire lengths (short, medium, long) and test each voltage setting for each length of wire. I will carry out one test for each voltage setting. I will use these results to compare with my main investigation to ensure that the results are reliable.

Prediction

I predict that the 4V setting will be the most suitable because I think that the 2v setting will be too low and will not produce high enough numbers which will be harder to use to calculate the resistance and take notice of the relationship between resistance and length, and the 6V setting will be too high and produce heat energy which will affect the results.

Middle

Prediction

I predict that the resistance will increase as the length of wire increases. I think this because length affects resistance. As the wire gets longer, there will be more free electrons for the electrical current to pass around. The resistance of a piece of wire (or component) tells us how much it slows the current down. If the free electrons are slowing down the electrical current, the resistance will be higher. For the same voltage, current flows more easily through a low resistance wire than a high resistance one.

This diagram shows the electrical current having to move around the free electrons, causing resistance and slowing down the current altogether.

Equipment List

Power pack

Length of wire

Wires

Crocodile clips

Ammeter

Voltmeter

Method

I will use various lengths of wire starting from 200mm and ascending in 100mm gaps until the wire is1000mm. I won’t do the experiment with a length of wire shorter than 200mm because the wire will get hot and cause irregularities as temperature affects resistance.

Conclusion

>

Voltage (volts)

Experiment 3

Voltage (volts)

Average Voltage

200

2.18

2.22

2.14

2.18

300

2.26

2.27

2.23

2.29

400

2.32

2.32

2.29

2.34

500

2.35

2.35

2.34

2.35

600

2.36

2.37

2.36

2.36

700

2.38

2.39

2.37

2.38

800

2.39

2.41

2.39

2.40

900

2.40

2.43

2.41

2.41

1000

2.42

2.44

2.42

2.43

I calculated the average resistance by dividing the average voltage by the average current.

 Length of wire (mm) Average resistance (ohms) 200 0.92 300 1.30 400 1.59 500 1.88 600 2.19 700 2.56 800 2.82 900 3.13 1000 3.47

Analysis

Evaluation

I think my results are reasonably reliable and accurate but do have a few anomalies. As resistance is proportional to length, the best fit line on my graph should go through zero and the majority, if not all the points on my graph. However, there are 3 points either side of the best fit line. I think that the three points that are above the best fit line have been caused by heat energy raising the temperature and therefore raising the resistance as the wires probably became too hot during the experiments. I think that the three points below the line have possibly been cause by loose crocodile clips. This would have caused the reading to be inaccurate. If the crocodile clips were not connected securely, the voltmeter and ammeter would have read the voltage and current to be lower than the actual voltage and current.

This student written piece of work is one of many that can be found in our GCSE Electricity and Magnetism section.

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