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What Factors affects the resistance of a wire?

Extracts from this document...

Introduction

What Factors affects the resistance of a wire?

Introduction:

The main aim of this experiment is to investigate how the length of a wire affects the resistance of a wire. Some variables that affect the resistance of the wire, relevant to this investigation include:

  1. Length
  2. Thickness (cross-sectional area)
  3. Temperature
  4.  Voltage
  5.  Resistance
  6. Material

The resistance of a conductor must stay constant in order for a graph of voltage against current to show a straight line.

The length of the wire will affect the resistance. This is because the longer the wire the further the electrons have to travel, making more collisions along the way which slows down electron flow. The type of material will affect the resistance due to electrons having to pass through the material. Electrons find it easier to pass through some materials than others. It is the free electrons that carry the electrical charge. The more free electrons in the outer shell of atoms, the more electrons there are to carry charge and the lower the resistance.The thickness of the constantan wire would also have an affect on the resistance because the larger the cross sectional area of a wire the smaller its resistance. Temperature affects the resistance of a wire because if the temperature rises it would make the atoms vibrate more violently and increase the resistance because there are more collisions between electrons and atoms.

...read more.

Middle

4.8

40

3.30

0.90

3.7

60

3.59

0.66

5.4

80

3.15

0.53

5.9

Wire.30. SWG- (VOLTAGE USED- 3 VOLTS)

Length (cm)

Voltage (V)

Current (A)

Resistance (    )

20

2.34

1.82

1.3

40

3.02

1.16

2.6

60

3.37

0.86

3.9

80

3.57

0.68

5.3

Wire.22. SWG- (VOLTAGE USED- 3 VOLTS)

Length (cm)

Voltage (V)

Current (A)

Resistance (    )

20

0.95

3.29

0.3

40

1.45

2.60

0.6

60

1.70

2.12

0.8

80

2.2

1.98

1.1

What were the results?

I was pleased with the results obtained from the preliminary experiment. The results in this experiment showed that:

  • As the length of the constantan wire increased, the resistance increased.
  • As the length of the constantan wire increased, the voltage increased.
  • As the length of the constantan wire increased the current decreased.

Changes to the preliminary experiment to ensure more reliable accurate results are shown on the next page.

Changes to Preliminary Work:

  • In the preliminary experiment, a range of different constantan wires were tested and used. However in the main experiment only one main constantan wire was used.
  • In the preliminary experiment, I only completed each length of the constantan wire once. This would prevent anomalous results form being spotted, which means that the results may have been inaccurate and unreliable. Therefore in the main experiment I shall repeat each length of the constantan wire three times. This will ensure more accurate and reliable results being obtained.
  • Be more accurate in my positioning of the crocodile clips for more accurate and reliable results.
  • Allow the wire to cool down for a few minutes after each result was gained. This will ensure that an increase in temperature does not affect the results. Doing this will make them as accurate as possible.

What were the equipment used in the actual experiment?

Apparatus:

  • Ammeter
  • Voltmeter
  • A metre rular
  • Crocodile clips
  • Constantan Wire (longer than 1metre) 28 SWG
  • Leads
  • Power Pack
  • Wires
  • Sellotape
...read more.

Conclusion

  • Wait 10 minutes for the wire to cool instead of just a couple of minutes, therefore the temperature of the wire should be the same each time and therefore not affect the resistance of the wire. This would increase the reliability of the results.

Reliability of the experiment is on the next page.

Reliability:  

The overall experiment was very reliable as there were no anomalous results on the graph and all points lie very close to the line of best fit showing that they are accurate and reliable.  

  • The predicted results line of best fit is close to the actual line of best fit. This also means that they are accurate and reliable.
  • It is also reliable as anomalous results were also repeated and not included in the calculation of the average resistance value.
  • Each result for each length of wire was also similar. Therefore the evidence definitely supports a firm conclusion.

Planning section:

You must carry out a calculation to work out predicted resistance values:

image09.pngimage08.png

 R = resistance (       )

                                        = resistivity (       )

                                     L = length of wire (       )

                                    A = cross sectional area ( m   )

  • 28 SWG constantan wire has a diameter of 0.357 mm. This had to be converted into meters: 0.376 = 0.000376 m

Resistivity of constantan wire is 4.9 x 10     m. 4.9 x 10    m = 0.000000049

  • To find the CSA of the wire, you must use the following formula:

                 Diameter        2     =       Radius

           0.000188 m           2     =    0.000188m

Area =      

A      =               x 0.000188

A      =               x 0.000000035

A      = 0.000000111 m

So the cross- sectional area of the constantan wire with a diameter of 0.376mm is 0.000000111m    .

The predicted results for each length of wire is shown on the next page.

1.)

...read more.

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