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# Resistance of a wire. Jack has been given a second hand D.C. dynamo and lamp. He wants to attach these to his bicycle and produce most light without blowing the bulb. What wire should he use?

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Introduction

GCSE physics coursework: Resistance of a wire

Scenario:

Jack has been given a second hand D.C. dynamo and lamp. He wants to attach these to his bicycle and produce most light without blowing the bulb.

What wire should he use?

Variables:

The variables in our investigation are…

• The length of the wire
• The diameter of the wire (SWG)
• The type of wire

Types of wire:

Nichrome: 80% Nickel 20% Chromium Alloy.

Constantan: 60% Copper 40% Nickel Alloy.

Copper

First of all we decided to test the resistance using a Multimeter. This would give us a rough idea about what the resistances of each wire are.

Our lengths of wire were all 30cm long.

Our results were as follows…

 WIRE RESISTANCE Ω Copper 0.6 Nichrome 1.2 Constantan 4.3

Later we realised that we were using wires with completely different SWGs.

To make it a fair test we needed to use wires with the same SWG.

We repeated the test using a length of 30cm and an SWG of 32.

Our results were as follows…                    Our results changed dramatically.

 WIRE RESISTANCE Ω Copper 0.9 Nichrome 5.8 Constantan 2.9

Testing the current + Voltage

Next we decided to test the current and voltage so that we could get a more accurate figure for the resistance.

We set up a circuit consisting of, a power pack, ammeter and variable resistor in series.

Middle

0.44

0.44÷0.12

3.667

As you can see there is a correlation between the SWG and the resistance, this is that the lower the SWG the lower the resistance. We now decided to back this up with results from a Multimeter.

 SWG Resistance (Ω) 18 0.5 24 1.3 26 1.7 32 2.8 34 4.5

Testing SWG using Multimeter …..

As you can see, the results aren’t exactly the same but they still show the correlation that the lower the SWG the lower the resistance. This is because I lower SWG has a smaller diameter; this allows more electrons to flow through the wire.

After this we decided to choose the SWG 18 constantan as the type and diameter of wire we used. This is because it has the least resistance yet it is the thickest, therefore it will not get to hot too easily.

Now we decide to test length to test which has the lowest resistance and which is the most practical, we are using the same circuit as we used earlier in our experiment except this time is the length. We tested 6 different lengths from 10cm going up in 10 cm to 60 cm.
We also kept the voltage on 2 volts; our results were as followed ….

 Length (cm) Voltage (V) Current (I) Resistance (Ω) 10 0.05 0.13 0.385 20 0.12 0.13 0.923 30 0.03 0.14 0.214 40 0.11 0.13 0.845 50 0.05 0.14 0.356 60 0.04 0.14 0.286

After taking these results we realised that there should have been a correlation between the length and the resistance, that is that the longer the wire the greater the resistance. We repeated the experiment and exchanged the variable resistor for a different one, after doing this we got these results …..

 Length (cm) Voltage (V) Current (I) Resistance (Ω) 10 0.01 0.15 0.02 20 0.01 0.14 0.09 30 0.02 0.14 0.14 40 0.03 0.14 0.21 50 0.03 0.14 0.27 60 0.05 0.14 0.36

Conclusion

Conclusion

For my wire I would like to you constantan wire with an SWG of 18 and a length of 35 cm. This is because the data I have collected suggests this will have the least resistance making it efficient and it is also a very practical length and diameter. I have the upmost confidence in the accuracy and reliability results and data I have collected and the only weakness is the lack of accuracy I received from the ammeters and voltmeters, but even with this weakness I still managed to get a correlation in the final test of my experiment. Another reason I have confidence in my results is because of the precision I made sure of in my testing, with this precision and correlations in all of my graphs I consider my choice of wire to be a successful choice. If I could have collected any more data in my tests it would be the choice of diameter in my wire. As I only had 5 to test a greater range in the diameters I had to choose from would have improved the accuracy of the final wire chose.

William Lavelle-Bowden 10 Triple

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