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Resistance of Wires.

Extracts from this document...

Introduction

Physics Sc1 Investigation:                                                      Fay Woodhall 11DGB

                                                                                                             Lymm High School

                                                                                                             Center No. 40109

Resistance of Wires.

Introduction

Re·sis·tance (rimage00.png-zimage00.pngsimage01.pngtimage02.pngns)
n.

  1. The capacity of an organism to defend itself against a disease.
  2. The capacity of an organism, a tissue, or a cell to withstand the effects of a harmful physical or environmental agent.
  3. The opposition of a body or substance to current passing through it, resulting in a change of electrical energy into heat or another form of energy.
  4. In psychoanalysis, a process in which the ego opposes the conscious recall of repressed unpleasant experiences.

I am investigating resistance in the form of the opposition to electric current. I am going to investigate one of the factors that affect the resistance of a metal wire.

Key Factors

  • Diameter of a wire. A wider wire means there will be an increase in the number of positive ions across the cross section; therefore there will be more collisions for the negative free electrons and more resistance.
  • Temperature of the wire. An increase in temperature means the ions in the wire gain energy and vibrate more in their fixed positions, making it more difficult for the free electrons to move past, and increasing the resistance.
  • Length of wire. The longer the length of the wire the more ions the free electrons have to collide with as they move along the wire.
  • Material of wire. Some materials contain ions that are packed very tightly together, where as other materials contain larger spaces in-between its ions. The larger spaces let the electrons move through more easily.
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Middle

100 cm

1.65

0.20

8.3

Constantan

32 SWG

50 cm

0.77

0.20

3.9

For my preliminary work I will not be using any length of copper wire because its resistance is to low to be measured precisely and it is too like the wires used within the circuit. I have also decided not to use 24 SWG constantan because the resistance is too low to be measured accurately, unless I use the longer lengths. The longer length would cause problems in accuracy because the wire twists, making it difficult to measure the length accurately. The 32 SWG constantan would be good to use for my investigation because it has a good range of resistances within a length of 1m and they are large enough to be measured with precision. I will use lengths of 25 cm, 40 cm, 55 cm, 70 cm, 85 cm and 100 cm. I will use this range of 5cm steps because I think that it will give better-spaced results. I am not going to use lengths lower than 25 cm the resistance would be too low to measure accurately and I will not use lengths longer than 100 cm because the twists in difficulty in handling could cause problems in accuracy when measuring the lengths against the metre rule.

Main Investigation

Diagram
Method

The apparatus will be set up as shown in the diagram.

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Conclusion

Comment on Method

My method has proved suitable but it could be improved. I could have also controlled the temperature better by using smaller current. However this would require a more sensitive Voltmeter and Ammeter to ensure precise readings. I would need a meter that read to 0.001A and 0.001V. Another way of improving my method is by ensuring the wire had a constant diameter along the whole length of the wire. I could do this by checking at various points of the wire with a micrometer that measures to 0.01 mm. In order to ensure the correct lengths of wire were maintained throughout the experiment I could have used smaller crocodile clips that would have a much tighter hold on the wire to prevent any slipping altering the measured length.

Additional Work

In order to obtain extra evidence and support and further my conclusion I could measure the resistance of smaller lengths of 32 SWG constantan wire. However this would require a different technique in which I would have to measure the resistance directly, using a multimeter set on the Ohms scale. Alternatively I could measure the resistance of small lengths by adopting the circuit used previously. I could use a variable resistor in order to enable finer control of the current. This method would require more sensitive ammeters and voltmeters, as the readings would be smaller.

...read more.

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