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An Investigation into the Effect of the Length of a Wire on its Resistance.

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Introduction

Physics Coursework                                                                                    Alice Parker

An Investigation into the Effect of the Length of a Wire on its Resistance

Introduction

        Even the best conductors of electricity slow down the flow of electricity a little. The amount of slowing that occurs as electrons pass through an object is the amount of electrical resistance. The greater the resistance, the lower the current that is able to pass through the wire. For a given voltage, material with high resistivity will inhibit the flow of electrons (or current) through it. Resistivity is the power of resistance. A dictionary defines resistivity as:

  1. The power or property of resistance
  2. Also called specific resistance. Elect. the resistance between opposite faces of a one-centimetre cube of a given material; ratio of electric intensity to cross-sectional area; reciprocal of  conductivity.

Many variables can affect the resistance of a wire. These include

  • Thickness – a thick wire will allow more current through and so it has a lower resistance.                                                                                  
  • Temperature – heat increases the kinetic energy of particles in the wire meaning the particles inside collide more resulting in a higher resistance.
  • Length – As the wire length increases, the current has further to travel and so the resistance increases. This is due to the number of particles in the wire which the electrons collide with.
  • Type of wire – Different types of wire have different resistances. This is their resistivity.

Resistance is measured in Ohms and can be found using Ohm’s Law. In Ohm’s Law, the potential difference measured in volts is divided by the current, measured in amps, to find the resistance, measured in Ohms . Therefore R=V

                      I

...read more.

Middle

image13.png    Using the thin nichrome wire      

image14.png     Using the thick nichrome wire

As it shows a greater variety of results, I have chosen to use the thin nichrome wire in this experiment.          

Method

I will take 80 centimetres of thin nichrome wire and set this up in the circuit shown in the pilot test with the crocodile clip as close as possible to the end of the wire. I will then measure using a ruler 10 centimetres from the edge of the crocodile clip and connect this point to the circuit in order to complete it. Next, readings will be taken from the voltmeter and ammeter in my circuit. I will take readings from the digital displays on both pieces of equipment every 10 centimetres up to 80 centimetres, as this will provide a wide range of results. The experiment will be repeated twice until I have a total of three ammeter and three voltmeter readings from 10 centimetres to 80 centimetres at 10 centimetre intervals, in order to ensure that my results are accurate. I will switch the power pack off between readings to keep the temperature lower as the temperature in the circuit will also affect the resistance.      

        Using these readings, I will calculate the resistance at each length along the wire. To do this, I shall divide the potential difference recorded at every stage by the corresponding current to find three resistances (measured in ohms) at each length. I will then determine the average resistance for each of the 8 lengths measured by adding the three resistance totals together and dividing the sum by 3.

...read more.

Conclusion

        To record the results of this experiment, I would again read the potential difference and current from a voltmeter and ammeter and using the formula R = V     calculate the resistance. Again, I would repeat

                      I

The experiment 3 times with each diameter and record an average.

Another possible experiment would be to change the wire material. This would mean that the wire diameter and length would need to be very accurately checked in order to create a fair test. This would give us information about the resistivity of different metals and would be an interesting experiment to carry out. I would try different metals such as copper, Iron and lead and use the formula R = V  to calculate the

                                                      I

resistance. I would then rearrange the formula

and insert the resistance recorded to calculate the resistivity of each metal.

        The wire temperature could also be adjusted, with the same length and diameter of wire used. This could be achieved with resistors varying in strength. It would be difficult to keep the wire at a constant higher temperature, however. In this experiment, as heat increases the kinetic energy of particles in the wire and therefore speeds up the movement of the electrons within the wire, I would expect the resistance to be higher at higher temperatures due to an increased number of collisions.

Bibliography

Physics for you – Keith Johnson

Physics ‘A’ level revision – Stephen Pople

Complete Physics – Stephen Pople

Letts A level Physics study guide – Jim Breithaupt and Ken Dunn

...read more.

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