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# What factors affect the resistance of a wire?

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Introduction

What factors affect the resistance of a wire?

In this experiment I am going to investigate what are the factors affecting the resistance of a wire.

## Research

A wire – A good way to describe resistance across a wire is by Ohm’s Law, which is that for many useful conductors there is a simple rule that connects current, voltage and resistance. If we double the applied voltage, the current is doubled. If we halve the voltage, the current is halved. This effect doesn’t work with all conductors, but is true for metals and for carbon, things change. The rule is;

For a given conductor at a constant temperature the current in it is proportional to the applied voltage.

This can also be written as the formulae I=V/R where R is constant. We can use this formulae to make calculations with all values of V for a given conductor. But we have to be careful, because the resistance might change if the conductor gets hot.

Why does a material have a resistance? – When a given energy source, such as a battery or generator, the size of the current that flows is decided by the resistance if the circuit. All conductors resist the flow of electric charge to some extent, but some are better at it than others.

Middle

As we are not changing the voltage, type of wire, width of wire or any other variable that could affect our results, this prediction in my opinion is strong and should work out to be quite accurate.

### Method

1. First connect all apparatus together as in diagram below
2. Select the length of wire you are going to test and place the clips and the required length.
3. Select the main power supply to 2Volts and move the rheostat to create a resistance until the Voltmeter reads 2Volts (we used the voltmeter because it is a more accurate device, hence a fairer test)
4. When the Voltmeter reads 2Volts, read off the result on the Ammeter and note it in the result table.

### Results

 Fixed Variable Value Type of Wire Width of Wire Voltage through Wire 2 Volts Voltage Reader Voltmeter

1st Test

 Length of Wire (cm) Voltage (Volts) Current (Amps) Resistance (Ohms) 100 2 0.30 6.666 90 2 0.35 5.714 80 2 0.40 5 70 2 0.43 4.651 60 2 0.58 3.448 50 2 0.61 3.279 40 2 0.80 2.5 30 2 1.10 1.818 20 2 1.60 1.25 10 2 3 0.666

Conclusion

#### Resistance

As both the Voltage and Current readings were classed as very accurate, this meant that the resistance was very accurate to, because this was calculated from both Voltage and Current readings.

1st and 2nd Results tables

Both tables show almost exact results and the averages are very close to both results in each table.

In the experiment some tasks could not be preformed exactly, these were;

• The length of the wire could not be completely exact, we used a ruler to measure it but more accurate ways could have been used but we did not have the access to these.
• Both Voltage and Ampere meters were not 100% exact but these were the best we had given what apparatus we could use.
• Input Voltage was not exactly 2 Volts yet a perfect voltage could not be taken from the equipment we had at our disposal.

If this experiment were to be preformed again and only having the apparatus we did use available, I would stick to these apparatus as they were very good and came about a fair test and good, accurate results.

There was not much in the way to improve reliability and accuracy but I could of devised a way of measuring the actual current flowing through the circuit as the Voltmeter and ammeter were not the most reliable of meters but were the best we had.

Robert White 10Fi

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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