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# Physics Coursework Paper

My aim is to see how the resistance of a wire changes when you change the length.

Method

Diagram of set-up: Apparatus needed:

Power Pack,

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Voltmeter,

Ammeter,

Constantan Wire,

2 Crocodile Clips,

A metre ruler,

Sellotape.

Set-up a circuit as in the diagram above.

Sellotape the wire to the metre ruler.

Set the Power Pack on to 2V.

Change the length of the constantan wire each time and record the ammeter and voltmeter readings. I will then calculate the resistance by dividing the voltage by the current.

Fair Test

I will not keep the power pack on for too long at one time because the wire will get hot and the particles may start to move around.

I will keep the power pack at the same voltage all the time.

I will use the same ammeter and voltmeter for the experiment and any repeats.

Range

To collect my results I have decided to take an ammeter and voltage reading. I am going to increase the length of the wire by 10cm each time going from 10 to a 100 cm.

Prediction

I predict that the longer the wire the more resistance it will have. I think this because the longer the wire the more particles there are for the electrons to bang into. When the electrons bang into the particles they lose energy.

Preliminary

Checking that I can get a reading from the two ends of my range. I can get a reading for a 100cm, I got 0.44 amps and 1.4 volts. For 10cm though I can only get a voltmeter reading of 0.6 volts. The current is too high for the meter to measure. So I have decided to change my ammeter to one that goes up to 5 amps instead of 1. On the new ammeter I still get the same readings for a 100cm as before. But I now get a reading for 10cm of being 0.6 amps.

Detailed Theory

Resistivity gives a constant value for a material, so that you can compare different materials. The resistance of 2 different wires is not necessarily the same. Resistance depends on:

Its length (l)

Its cross-sectional area (A)

The material of which it is made

? is the resistivity of the material from which the wire is made

of. It says that for the constantan wire that I am using

? should equal 4.9 X 10ï¿½ m. When I get my results I will

check them against this figure to tell how accurate they are.

So to my results tables I have added the column length divided by area which is the other part that I need to work this out as well as the resistance.

RESULTS

Ist time

Length of Wire (cm)

Voltage (volts)

Current (Amps)

Resistance

(ohms)

10

0.8

2.0

0.4

20

1.0

1.5

0.7

30

1.2

1.2

1.0

40

1.3

1.0

1.3

50

1.4

0.8

1.8

60

1.4

0.8

1.8

70

1.5

0.7

2.1

80

1.5

0.6

2.5

90

1.5

0.5

3.0

100

1.6

0.4

4.0

Ist Repeats

Length of Wire (cm)

Voltage (volts)

Current (Amps)

Resistance

(ohms)

10

0.8

2.0

0.4

20

1.0

1.4

0.7

30

1.2

1.1

1.1

40

1.3

1.0

1.3

50

1.3

0.8

1.6

60

1.4

0.7

2.0

70

1.5

0.6

2.5

80

1.5

0.6

2.5

90

1.6

0.5

3.2

100

1.6

0.5

3.2

Comparing my two lots of results I still think that there are some which don’t quite look right so I have decided to do one more set of repeats.

2nd Repeats

Length of Wire (cm)

Voltage (volts)

Current (Amps)

Resistance

(ohms)

10

0.7

1.9

0.4

20

1.0

1.4

0.7

30

1.1

1.1

1.0

40

1.2

0.9

1.3

50

1.3

0.8

1.6

60

1.4

0.7

2.0

70

1.4

0.6

2.3

80

1.5

0.6

2.5

90

1.5

0.5

3.0

100

1.5

0.3

5.0

In working out my averages for resistance I decided to leave out the result I got for 100cms of wire on my 2nd repeats (5.0 ohms) because from comparing my results I think it is an anomaly.

Averages

Length of Wire (cm)

Resistance

(ohms)

Length divided by Area

(metres)

10

0.4

628760.269

20

0.7

1257520.538

30

1.0

1886280.807

40

1.3

2515041.076

50

1.7

3143801.345

60

1.9

3772561.614

70

2.3

4401321.883

80

2.5

5030082.152

90

3.1

5658842.421

100

3.6

6287602.690

I have now worked out the average resistance and the average length divided by area. So I now have everything I need to compare my results to the figures I got from the book.

Graphs

CONCLUSION

My results show me that the longer the piece of wire is, the more resistance there will be. This is what I predicted would happen in my prediction. I think this happened because the more wire there is the more particles there are to bang into, which slows down the electrons. I also found that Resistance and Length are proportional, I could tell this by the straight line of best fit that I got on my first graph.

From my 2nd graph I took the gradient of the line of best fit this represented the Resistivity of a constantan wire. I got 0.00000052m the book says for a constantan wire the resistivity should be 0.00000049 metres. Comparing these figures I would say that my results were quite accurate as the difference is 0.0000003m.

EVALUATION

From my method I was able to easily achieve a set of results. I think that the method I chose to use was quite reliable. If I were to do this investigation again I would come up with a better way of doing it though to get more accurate results because the wire kept bending so I am not sure that the distances we measured at were very precise.

As I mentioned before I think that I only had one anomaly and did not use this in working out my averages. I think we got this anomaly because near to the end of the investigation we started to rush becoming a bit more careless, maybe living the power pack on which would of increased the resistance because the wire would have been hotter.

Firm conclusions that I can make are:

* The longer the wire the more resistance there will be.

* Resistance and Length are proportional.

* Resistivity of a constantan wire is about 4.9 X 10 metres.

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