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In this investigation I'll attempt to find out how electrical resistance varies for two different conductors, nichrome and constantine, when changing the length and the thickness of the wire.

Extracts from this document...

Introduction

Mitchell Black                Physics Coursework

Physics Coursework

Investigation into the Factors affecting the Resistance of a Conductor

By Mitchell Black

April 2003

Introduction

In this investigation I’ll attempt to find out how electrical resistance varies for two different conductors, nichrome and constantine, when changing the length and the thickness of the wire.

Variables

  1. Length – The longer the length of the wire the further the electrons will have to travel along it, increasing the resistance. Because of this the length increase should be proportional to resistance increase.
  2. Cross section of the wire - If the wires width is increased the resistance will decrease. This is because of the increase in the space for the electrons to travel through. Due to this increased space between the atoms there should be less collisions.
  3. Voltage passed through the wire – The higher the voltage the more electrons there will be passing through the wire, this should cause more collisions, causing higher resistance.
  4. Temperature – Resistance produces heat, but heat also increases resistance. This is because the atoms in the wire vibrate more due to their increased energy. This causes more collisions with the electrons as the atoms vibrate into the path of the electrons.
  5. Type of wire used – Obviously different conductors have different resistivity, so the same conductor should be used throughout the experiment.

For this experiment I will keep voltage, temperature, and the type of wire used constant.  I shall vary length and cross section of the wire, as these are the factors I’m investigating.

...read more.

Middle

  1. Steps 1-5 will then be repeated with Nichrome wire of width SWG26 SWG28 SWG36 and SWG40.
  1. The same will be done for Nichrome wire.

As the SWG number increases the cross sectional area of the wire decreases.

Results

Results for different thicknesses of Constantine wire

Length

Resistance SWG 22

Resistance SWG 26

Resistance SWG 28

Resistance SWG 36

Resistance SWG 40

5cm

0.9

1

0.8

1.7

2.8

10cm

1

1.1

1

2.5

4.9

15cm

1.1

1.3

1.3

3.2

7.2

20cm

1.1

1.3

1.5

4

8.9

25cm

1.4

1.7

1.6

4.7

11.1

30cm

1.6

2.1

1.9

5.5

12.9

35cm

1.3

2.5

2.1

6.4

16.6

40cm

1.6

3.0

2.6

7.3

17.3

Results for different thicknesses of Nichrome wire

Length

Resistance SWG 22

Resistance SWG 26

Resistance SWG 28

Resistance SWG 36

Resistance SWG 40

5cm

1.0

2.1

2.2

3.7

7.3

10cm

1.1

2.4

2.8

5.7

11.1

15cm

1.3

2.7

3.3

7.6

16.3

20cm

1.5

3.1

3.8

9.4

20.7

25cm

1.7

3.4

4.3

11.4

26.0

30cm

1.8

2.8

3.6

12.1

29.3

35cm

2.2

4.0

5.2

15.2

35.2

40cm

2.4

4.4

5.9

17.4

40.6

Area of Nichrome wire

SWG

Radius (cm)

Resistance (ohms)

Area (cm)

Area x 10  

1/area

22

0.0355

1.2

0.00396

39.6

252.52

26

0.0225

2.8

0.00159

15.9

628.93

28

0.02

3.6

0.00126

12.6

793.65

36

0.01

12.1

0.000314

3.14

3184.71

40

0.006

29.3

0.000113

1.13

8849.56

...read more.

Conclusion

3 bar enough to effect results than a 2cm3 wire.Looking back on the procedure of my experiment I now realise that I should’ve taken 3 readings, and then found the average in order to gain more accurate results.I think that some of my anomalous results may be accounted for due to bad contact through the crocodile clip.  The only way I can see to get round this problem is to have boards especially made for this experiment, which have a sliding contact, which you slide to the correct length, and then somehow secure it to the wire.

Anomalies

The only anomalies I could identify were on the curved graph for constantine (area: resistance), it was using the SWG 28 board.  In turn affecting the graph for 1/Area of constantine, with an anomaly also on SWG 28To me this suggests that the board was faulty, maybe there was a kink or a bend in the wire.  I’ve circled this results on the graph.  Also I’ve marked in where I’d expect it to be in pen.

Further Work

To take the investigation one step further, other factors could be investigated, such as voltage.  Using the same two metal wires, on a relatively medium thickness (such as SWG 28), connected to an ohmmeter.  The voltage should be increased, and the resistance reading recorded each time.  I think this investigation would show that as the voltage increases so does the resistance, because more voltage means more electrons moving around and colliding, and colliding electrons cause resistance.  The graph would look something like the sketch below.

Resistance                      

      (Ω)

                         Voltage (Volts)

...read more.

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