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# Resistance of a wire coursework

Extracts from this document...

Introduction

Resistance of a wire coursework

Increasing the number of cells in a battery increases the potential difference across it. Potential difference is a measure of the battery’s ability to push current through the circuit, so increasing the number of cells increases the current and makes lamps brighter. The lamps however push against the current and tend to stop it flowing- we call this behaviour resistance.

The current through a component in a circuit (a lamp, for example) is affected by both the potential difference and the resistance. If we measure the potential difference against a component in a circuit and the current through it, we can calculate the resistance by using the relationship

Potential difference= current * resistance

(Volts, V)          (Amperes, A) (Ohms, Ω)

Resistance is measured in ohms. A component has a resistance of 1 ohm if a current or 1 amp flows through it when there is a potential difference of 1 volt across it. The symbol Ω is sometimes used instead of the word ohms.

Resistors are used to reduce the size of electric currents in electronic circuits. The resistors on a circuit board are the components with the coloured stripes.

To help us understand what is happening in the current we use a model of the circuit. Scientists use models when they want to simplify things they are studying- this helps them to make predictions, which they can then test using experiments.

Electricity flowing through wires behaves like water flowing through pipes.

Middle

3.29

80

1.27

0.35

3.63

90

1.31

0.29

4.52

100

1.33

0.29

4.59

Wire 1, Set 2:

 Length (cm) Voltage (V) Current (A) Resistance (W) (to 2 d.p.) 10 0.51 1.02 0.50 20 0.79 0.79 0.97 30 0.91 0.65 1.40 40 1.02 0.55 1.85 50 1.08 0.48 2.25 60 1.15 0.42 2.74 70 1.19 0.37 3.22 80 1.22 0.33 3.70 90 1.26 0.30 4.20 100 1.27 0.28 4.54

Having completed two sets of results for one wire, it was noticed that these was a large black mark towards one end of the wire, where it appeared that it had been melted to some degree at some point. It was therefore decided to conduct experiments on an additional piece of wire that was checked for integrity prior to investigation:

Wire 2, Set 1:

 Length (cm) Voltage (V)

Conclusion

Wire 2, on the other hand, had three main anomalous results: at 50, 80 and 90cm. They are by no means that far off but in an experiment such as this, which is generally a very accurate one anyway, such anomalous results should not be quite so common. Possible explanations for these anomalies are as follows:
• The length of wire for that particular measurement was not correct. At 50 and 80cm it is possible that the length was shorter, causing a lower resistance, and at 90cm it is possible that it was longer, causing a higher resistance. The solution to this is to measure the lengths more carefully and ensure that the wire is pulled tight against the metre rule.
• For a particular result, one or more of the connections could have been faulty, causing extra resistance at the connections. A solution to this would be to, before each experiment, connect the connections together without the wire in place and measure the resistance then. If it is higher than it should be then the connections could be cleaned.
• Whilst extremely unlikely, it is conceivable that the power supply was providing a different voltage for some of the results. This is unlikely to be a problem in this investigation but it might have been an issue had we used batteries instead.

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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