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# The aim of this coursework is to investigate one factor that affects the resistance in metallic wires.

Extracts from this document...

Introduction

Martin Smith 11Ba2

Key Stage 4 Physics Coursework - Resistance of wires

The aim of this coursework is to investigate one factor that affects the resistance in metallic wires.

Background Information

What Is Resistance?

Resistance is when the metal ions in a wire oppose the flow of electrical current carried by the electrons.

Mathematical Information About Resistance

The Ohm (Ω) is the unit of resistance and is always written as a capital letter. Throughout this coursework that symbol will appear to represent a unit of resistance.

The Mathematical general equation that is used to find resistance is:

R    =    V

I

R = Resistance (Ω)

V = Voltage or pd

I = Current (Amps)

This is known as Ohms law. The equation means that resistance is proportional to pd and inversely proportional to the current as long as the temperature is constant. The reason why temperature is important is because the slightest increase in temperature could cause the atoms in a wire to vibrate more which would change the resistance of the wire. This idea will be explored further in future sections of this coursework

You can use this formula to find the resistance of an electrical component. You need to know the current by measuring the number of amps across the component using an ammeter. You also need to know the voltage or pd across the component and you would measure that using a voltmeter.

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Middle

20cm

1.0

50cm

2.4

100cm

4.6

Constantan

32

20cm

1.6

50cm

4.1

100cm

7.9

The results above have enabled me to gain an idea of what wire to use. Copper is definitely not a good idea, mainly because it does not give a wide enough spread of results. Nichrome is a possibility, because it gives a good spread of results, but may be a good idea to try with a higher SWG rating. Constantan gives a good spread, however, it has a high SWG rating, but a spread of results that is not that much better than Nichrome 24. Therefore, I shall repeat the experiment, but with Nichrome and a higher SWG rating. I shall use Nichrome 36.

 Material SWG Length/cm Resistance/Ω Nichrome 36 20cm 7.5 50cm 18.5 100cm 38.1

It is clear from these results that there is a good spread here. The SWG rating is not really any higher than the Constantan but gives a much better spread of results. Therefore, I shall use Nichrome 36 within my main experiment.

Main Investigation

Purpose Of Work

The purpose of this work is to investigate how lengths affect resistance.

List Of Equipment

The Equipment that I shall use for this experiment will be:

• Power pack (set at 3 Volts)
• 6 Leads
• Ammeter
• Voltmeter
• 2 Crocodile Clips
• 100cm length of Nichrome 36 wire

Circuit Diagram

Key

Wire

Ammeter

Voltmeter

Variable Resistor

Method

This method has to be fair, for that reason, the experiment will be carried out three separate times, each time the settings of each device will remain the same and the entire experiment will be carried out within one lesson to ensure that between the change in day, errors cannot be made in terms of changing a vital settings, such as a change in volt settings on the power pack. The material (Nichrome) will be used in each experiment and that will be checked before the start of the experiment. We will also be using a wire with SWG rating 36, this shall also be checked before the start of the experiment. The variable resistor also needs to have the same setting each time. We shall ensure that the variable resistor is not at all touched and therefore the setting on that shall remain the same at all times.

1. Firstly, assemble the equipment. Gather up the required equipment using the list above and use the circuit diagram above to correctly put it together. The ammeter is actually put in series with the rest of the circuit, whereas the voltmeter is put in parallel at the appropriate section. Simply put the wires coming off from the voltmeter into the slots on the wires with the crocodile clips on that you attach to the wire. Set the Variable resistor to any setting, but not too high. For the variable resistor, one wire needs to go into one of the two sockets on one end, and then another wire needs to come out at the other end in the only socket that a wire can be put into.
1. Put the Nichrome wire in-between the crocodile clips. The wire must be put at the appropriate lengths (10cm, 20cm, 30cm, 40cm, 50cm, 60cm, 70cm, 80cm, 90cm and 100cm). One crocodile clips is fixed, the other can be unclipped and put at the fore mentioned intervals.
1. When you turn on the power pack which should be set at 3 Volts, and have ensured the Nichrome wire is at the length interval you require, take the reading from the voltmeter and the ammeter. Ensure that these results are correct.
1. Repeat step 3 for each interval. Then repeat the entire experiment throughout and take readings and record the results once again and make sure the variable resistor is at the same setting and that the power pack has the same number of volts (3 Volts)

Results

Nichrome 36

Results from the experiment the first time around:

 Length Volts Current (Amps) Resistance Ω 10cm 0.96 0.47 2.042553191 20cm 1.58 0.42 3.761904762 30cm 2.14 0.38 5.631578947 40cm 2.58 0.35 7.371428571 50cm 3.00 0.31 9.677419355 60cm 3.27 0.29 11.27586207 70cm 3.55 0.27 13.14814815 80cm 3.76 0.26 14.46153846 90cm 4.02 0.23 17.47826087 100cm 4.14 0.22 18.81818182
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Conclusion

Quality Of Graph

There were no ominous results on my graph. This is both a good and bad thing. This is good, because it shows how good my procedures and testing methods are, but it is bad because it makes me suspicious as to whether my experiment was that perfect. I would expect an ominous result, or at least more results that went away from the line of best fit. They seem to fit an obvious pattern, and therefore make it harder to improve upon.

Fairness Of Testing Conditions

I believe that my test conditions were fair, and that all stages were checked thoroughly. The lengths were checked regularly to ensure they were correct, and the materials were checked too. The settings of the variable resistor and the power pack were never altered. Therefore, I believe that my test conditions were as fair as I could make them in the classroom environment.

Mini Plan Further Experiments

If I was going to do this experiment again, then I would allow more time to be allotted to carry out the experiment and to be able to ensure that all fair test methods were more strictly adhered to. I would also carry out more experiments at more intervals, and do for instance 5cm, 10cm, 15cm etc. Those are the only improvements I feel can be made.

Conclusion

In conclusion, I feel that I have proved my prediction that as the length increases the resistance also increases. I feel the experiment was performed well and gave me satisfactory results.

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