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Investigation to find out what factors affect the resistance of a wire?

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Introduction

Sarah Roberts

Mars 10

July 2001

Physics Coursework: Investigation to find out what factors affect the resistance of a wire?

Introduction and predictions

I have been set the task of finding out what factors affect the resistance of a wire. Firstly I know ohm’s law which states that voltage is equal to the product of current and resistance. This can be written as V= IR where V is voltage, I is current and R is resistance.

So the formula for resistance is - Resistance = Voltage (ohms)

                                                                           Current (amps)

To work out my predictions I need to look at the scientific knowledge I have gathered. I used my exercise book, information booklet, and the science and technology encyclopaedia by Marshall Cavendish. I also looked at the preliminary work I did in class. In my preliminary work I did an experiment to find out about the resistance of a wire. This is the circuit I set up.

I found out that the ratio of voltage to current is always the same whatever the two values are. The resistance is therefore always the same in a fixed length of wire. I want to find out how the resistance of a wire depends on other factors. I shall now make my predictions as to what I think will happen. I think that the resistance of a wire will depend on 1. The length of a wire

                     2. Thickness of a wire

                     3. Type of metal

I have made these predictions by looking at my scientific knowledge. I shall now explain why I think that those are the factors that resistance depends upon.

...read more.

Middle

Record the resistance in a table
  1. Proceed to connect the next wire to the circuit

Results for both experiments

All results have had 00.2 taken away for the leads

Experiment 1

Length of wire

(cms)

Resistance (Ω)

Constantan

   1       2       Avg

Nichrome

   1          2       Avg

Manganin

     1        2      Avg

20

0.6

0.6

0.6

1.4

1.4

1.4

1.1

1.1

1.1

40

1.3

1.3

1.3

2.8

2.8

2.8

1.1

1.1

1.1

60

1.7

1.7

1.7

4.3

4.3

4.3

1.5

1.5

1.5

80

2.4

2.4

2.4

5.6

5.6

5.6

2.3

2.3

2.3

100

3.0

3.0

3.0

6.7

6.7

6.7

2.7

2.7

2.7

Diameter- 20swg

Experiment 2

...read more.

Conclusion

not vary appreciably with temperature. Therefore it probably was not a change in temperature which produced this anomalous result. It is likely that the resistance value was misread or that there was a mistake in the calculations where 00.2 was removed from each value to account for the leads.

        If I were to conduct the experiment again I would ensure that all readings were taken on the same day, as I do not think they were. Especially as I have learned that fluctuating temperatures can vary the resistance. I would also consider taking 3 readings instead of two and then getting an average. This would give me more accurate and reliable results. It would also be better if one person was assigned to taking the readings and one to deducting 00.2 from the readings. This would be better than people switching jobs, which might cause discrepancies in the results. Now that I have looked at how length, thickness and the metal of the wire affect resistance, I could also look at how temperature affects the resistance of a wire. I could also extend the experiment by taking into account these four factors all at once and looking at how the electrical conductivity varies.

...read more.

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