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Investigating the factors affecting the resistance in a piece of wire.

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Introduction

Helen Bewick 10C

Investigating the factors affecting the resistance in a piece of wire

Planning

Resistance- Resistance is a force which opposes the flow of an electric current around a circuit so that energy is required to push the charged particles around the circuit. Resistance is measured in ohms.

During this experiment I aim to research and plan an experiment to investigate a factor that affects the resistance in a piece of wire.

The possible factors I could change in this investigation are:

  1. Length of the wire,
  1. Thickness of the wire,
  1. Type of metal- Copper, Nichrome and constantan
  1. Shape of the wire,
  1. Temperature of the wire,
  1. Density of the metal.

I have chosen to investigate the length of the wire because length is a continuous variable with a continuous range so I will be able to choose any lengths to investigate.

I chose not to investigate thickness because although it is a continuous variable the wires available to me only come in set thickness that do not go up in regular intervals.

I chose not to investigate type of metal because it is not a continuous variable so I would not be able to evaluate the investigation by linking two or more groups of data on a graph.

I chose not to investigate the shape of the metal because it isn’t a continuous range. I could only use two options bent or straight.

I chose not to investigate the temperature because although it is a continuous range it is very difficult to maintain a temperature, as you couldn’t use a water bath because of safety aspects. It is also difficult to measure the temperature of a piece of wire.

...read more.

Middle

The resistivity of Nichrome at 250C is 100 x 10-8 ohm-m. The radius of the wire is 0.00014m2. To find the area of a cross section of the wire i use the equation for the area of circle

Area of circle = πr2

Area of circle  = π x 0.000142

Area of circle = 6.16m2 x10 -8

Working to find the resistance

To predict resistance for a length of wire of 10cm I use the equation,

Resistance  = resistivity x length / area of cross section of the wire

Resistance = 100 x 10-8 x 0.1m / 6.16m2 x 10 –8

Resistance = 1.62 Ω rounded 2 d.p.

To predict resistance for a length of wire of 20cm I use the equation,

Resistance  = resistivity x length / area of cross section of the wire

Resistance = 100 x 10-8 x 0.2m / 6.16m2 x 10 –8

Resistance = 3.25 Ω rounded 2 d.p

To predict resistance for a length of wire of 30cm I use the equation,

Resistance  = resistivity x length / area of cross section of the wire

Resistance = 100 x 10-8 x 0.3m / 6.16m2 x 10 –8

Resistance = 4.87 Ω rounded 2 d.p

To predict resistance for a length of wire of 40cm I use the equation,

Resistance  = resistivity x length / area of cross section of the wire

Resistance = 100 x 10-8 x 0.4m / 6.16m2 x 10 –8

Resistance = 6.49 Ω rounded 2 d.p

To predict resistance for a length of wire of 50cm I use the equation,

Resistance  = resistivity x length / area of cross section of the wire

Resistance = 100 x 10-8 x 0.5m / 6.16m2 x 10 –8

Resistance = 8.12 Ω rounded 2 d.p

To predict resistance for a length of wire of 60cm I use the equation,

Resistance  = resistivity x length / area of cross section of the wire

Resistance = 100 x 10-8 x 0.6m / 6.16m2 x 10 –8

Resistance = 9.74 Ω rounded 2 d.p

To predict resistance for a length of wire of 70cm I use the equation,

Resistance  = resistivity x length / area of cross section of the wire

Resistance = 100 x 10-8 x 0.7m / 6.16m2 x 10 –8

Resistance = 11.36 Ω rounded 2 d.p

...read more.

Conclusion

  • I left the power pack on too long. This causes the wire to overheat.
  • When I was measuring the lengths of the Nichrome wire my measurements might have been slightly inaccurate. The rulers used might not have been exact and it was difficult to get an accurate reading of length by eye as the wire was not completely straight. Also the ruler may have been of different thicknesses throughout the length. This would have contributed as a slight error in my results.
  • The ammeter and voltmeter could have been slightly faulty and not given me correct, accurate readings.
  • I connected the wire into the circuit using crocodile clips. These were quite loose and so this could have made my results less accurate. If I improved my method I could either attach the wires with tape but this may affect my results so instead I could solder the Nichrome wire into my circuit.
  • It was difficult to adjust the variable resistor slider accurately only by eye. If I did the investigation again I could try to and adjust the variable resistor accurately I will use an advanced digital variable resistor.
  • I also found it difficult to measure exact lengths against the meter rule because the crocodile clips didn’t clip on to the wire very securely. If I did the investigation again I could pre cut all the lengths of wire before the experiment instead of just connecting the crocodile clips at different distances apart on the meter rule.  

        To further my investigation I could use the same method but increase the range of lengths. I could use lengths of up to 3 meters. I could take readings from lengths at smaller intervals; I could take reading every 5cm instead of every 10cm as I did. I could also take more repeat readings to get a even more accurate average.

...read more.

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