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

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 10¯ 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)

0

0.8

2.0

0.4

20

.0

.5

0.7

30

.2

.2

.0

40

.3

.0

.3

50

.4

0.8

.8

60

.4

0.8

.8

70

.5

0.7

2.1

80

.5

0.6

2.5

90

.5

0.5

3.0

00

.6

0.4

4.0

Ist Repeats

Length of Wire (cm)

Voltage (volts)

Current (Amps)

Resistance

(ohms)

0

0.8

2.0

0.4

20

.0

.4

0.7

30

.2

.1

.1

40

.3

.0

.3

50

.3

0.8

.6

60

.4

0.7

2.0

70

.5

0.6

2.5

80

.5

0.6

2.5

90

.6

0.5

3.2

00

.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)

0

0.7

.9

0.4

20

.0

.4

0.7

30

.1

.1

.0

40

.2

0.9

.3

50

.3

0.8

.6

60

.4

0.7

2.0

70

.4

0.6

2.3

80

.5

0.6

2.5

90

.5

0.5

3.0

00

.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)

0

0.4

628760.269

20

0.7

257520.538

30

.0

886280.807

40

.3

2515041.076

50

.7

3143801.345

60

.9

3772561.614

70

2.3

4401321.883

80

2.5

5030082.152

90

3.1

5658842.421

00

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.