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What factors affect the flow of current through a wire?

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Introduction

Sreekar Charlu 1VCB                                                                             14th March 02

Physics Coursework

What factors affect the flow of current through a wire?

Planning

Theory

Current is due to the flow of electrons. The material of the wire consists of layers of atoms whose positive centres (ions) are surrounded by a sea of electrons. These electrons are very mobile (free to move). However, when the electrons start moving, carrying current, they will keep on bumping into the ions. These ions, vibrating in fixed positions, cause obstruction to the free flow of electrons. This obstruction is termed resistance. Resistance opposes current and therefore the higher the resistance, the smaller the current. Therefore the factors that affect the resistance are the same factors that control the flow of current through a wire.

image00.png

In the above diagram the circle represent the ions and the red line represents the flow of electrons.

The factors affecting the flow of current, which you could investigate, are:

  • Area of cross-section of wire

When the area of cross-section of the wire is increased the current through it will increase. This is because the electrons can flow more freely through a large cross-section space available, with the same length of wire, and so avoid colliding

  • Length of wire

When the length of wire is increased the current is expected to decrease.

...read more.

Middle

0.21

0.16

4.76

0.762

100

0.18

0.16

5.56

0.890

  1. Table of Results

Length (cm)

Current (A)

Voltage (V)

image10.png

Resistance (ohms)

10

1.63

0.16

0.613

0.098

15

1.29

0.16

0.770

0.123

20

0.91

0.16

1.10

0.176

25

0.71

0.16

1.41

0.2256

30

0.67

0.16

1.49

0.2384

35

0.57

0.16

1.75

0.280

40

0.44

0.16

2.27

0.3632

45

0.42

0.16

2.38

0.3808

50

0.40

0.16

2.50

0.400

55

0.36

0.16

2.78

0.4448

60

0.33

0.16

3.03

0.4848

65

0.31

0.16

2.23

0.568

70

0.28

0.16

3.57

0.5712

75

0.27

0.16

3.70

0.592

80

0.25

0.16

4.00

0.640

85

0.23

0.16

4.35

0.696

90

0.23

0.16

4.35

0.696

95

0.23

0.16

4.76

0.7616

100

0.18

0.16

5.56

0.889

  1. Table of Results

Length (cm)

Current (A)

...read more.

Conclusion

image14.png, with the gradient from my graph, a value of image15.pngwas obtained for the specific resistance (image16.png) of constantan which worked very well with the literature vale (ref. Electricity made simple). These facts clearly show that my investigation was very successful and accurate. However, I did find some anomalous results which I could make more reliable throughout extended investigations.

        Nevertheless, there were several areas that could have been improved. Accurate measurement of lengths is one such area and choosing wires of 100% uniform thickness with minimum requirements for straightening would help to increase accuracy and avoid anomalous values in the results. While random errors can be minimised by doing each step extra carefully any systematic errors due to instruments such as the ammeter and voltmeter can be overcome only by calibrating the ones used against accurate instruments.

        Repeating each experiment under identical conditions will ensure reproducibility. Both reproducibility and accuracy are required in order to obtain an extremely successful outcome of an investigation. Using different thickness of wire could extend this experiment and also by using different materials, in order to demonstrate the correctness of the relationship image17.pngimage12.png for the resistance of the wire. I could also extend this experiment by using different sets of cross-sections of the wire so I could prove which had the highest resistance and which one had the lowest resistance.

...read more.

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