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Investigation into the Resistance in different lengths of wire

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Introduction

Investigation into the Resistance in different lengths of wire

Introduction

In this investigation, I will be looking at how the resistance in a piece of wire changes when I change the length of the wire. The variable in the experiment will be the length, and the thing I am studying will be the resistance.

Equipment

  • For my experiment I will need:
  • Wires of set length - for connecting the circuit together
  • A Variable Power Pack - to give the experiment its power and so that I can adjust the current to a suitable level
  • Wire that I can cut and adjust - this is the wire I will be testing though, so it must be bare.
  • Crocodile clips, to secure the wire
  • Voltmeter - to measure the voltage
  • Ammeter - to measure the current

Diagram

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A

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Method

I will set up the experiment as shown above, and then connect the 100cm wire to the crocodile clips, and turn the power on. Then I will take a reading of the Ammeter and Voltmeter, and record them. Then I will remove this wire, and replace it with a 90cm long wire, take a reading, and remove it. I will do the same for the 80cm, 70cm and so on, until I have reached 0cm. I have decided to use wire at 10cm intervals because it gives a nice even spread over the 100cm range, and it is small enough for me to see where anomalies are. So this means that if anything goes wrong, I can easily see it.

...read more.

Middle

∝ L, where R is the resistance, and L is the length of wire. If my prediction is correct, I should see a straight line on my graph.

Results

Here are the results for my experiment...

the first time:

Length of wire (cm)

Voltage

(V)

Current

(A)

Resistance

(Ω)

100

1.66

0.08

20.75

90

1.66

0.09

18.44

80

1.66

0.10

16.60

70

1.66

0.11

15.09

60

1.62

0.13

12.96

50

1.60

0.16

10.00

40

1.57

0.19

8.26

30

1.55

0.25

6.20

20

1.50

0.38

3.95

10

1.39

0.70

1.99

the second time:

Length of wire (cm)

Voltage

(V)

Current

(A)

Resistance

(Ω)

100

1.66

0.08

20.75

90

1.66

0.09

18.44

80

1.66

0.10

16.60

70

1.64

0.11

14.91

60

1.62

0.13

12.96

50

1.60

0.17

9.41

40

1.58

0.20

7.90

30

1.55

0.26

5.96

20

1.50

0.38

3.95

10

1.39

0.70

1.99

...read more.

Conclusion

R ∝ L

∴ R = k L

∴ k = R/L

subst. When L = 10, R = 1.98

∴ k =  1.98/10

∴ k  = 0.198

∴ R = 0.198 x L

I have found that the formula for the resistance in this piece of wire was approximately 0.198 x the length of the piece of wire. I can now determine the resistance for any length of this type and quality of wire.

Evaluation

I think that the method we used and the results we obtained were both suitable and acceptable for the experiment, because they both fitted quite neatly with the experiment itself. The results were in the range I expected, and the method was not over-complicated, but it was still fairly practical. Looking at my title and introduction, I have done what I set out to do.

        I think that the least accurate part of the investigation was probably me, because my measuring probably could have been a lot more accurate if I had taken more time and care over it, but I am happy with the results and method I got.

        There were no highly anomalous results, and those that were slightly out of sink, I have explained in my ‘anomalies’ section. If I were to do this investigation again, I think I would probably not change much, but just try and be a little more accurate.

...read more.

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