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Resistance Wire Investigation.

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Introduction

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Aim: To investigate the effects of a resistance wire in an electrical circuit.

Key Factors: The Key Factors in this experiment are

  • Volts - the amount of batteries in the circuit
  • Length - the length of resistance wire in the circuit
  • Type - Different types of resistance wire made from materials e.g. copper or aluminum.
  • Circuit - whether the resistance wire is in series or parallel
  • Components - how many bulbs, switches or motors etc. are in the circuit.
  • Thickness of the wire- How thick the wire is in mm
  • Insulated or not- if there are any materials insulating the wire in the circuit.
  • Shape of wire- if the wire is bent out of shape

I have chosen to do the length of the wire.

Prediction

I Think that the longer the wire the more resistance in the circuit. I think that for a 20cm length of wire, the resistance will be double the length of a 10cm wire.

The longer the wire the longer it takes for the current to travel through. If I use a high voltage on a small piece of wire the wire will burn out due to a high current. The electrons passing through the circuit on their way around the circuit have to push their way through a lot of atoms. The atoms resist the passage of electrons through the wire.

The resistance is measured in units called ohms.

...read more.

Middle

Plan:

I will put together the same circuit to that I used in the preliminary practical.

I will use the following equipment:                 

A power pack

                        An ammeter

                        A meter of resistance wire

                        Crocodile clips

                        Circuit wire

                        A meter ruler

                        A voltmeter

I will use a 4Volt power pack. One end will be permanently connected to one end of a meter length of wire. The other end will be connected via an ammeter in series to a crocodile clip, which can be connected at any point over the meter length of wire. I will attach the wire to the meter ruler so I am able to clip the crocodile clips on at different lengths. From the preliminary practical, the lengths are: 10cm, 20cm, 30cm, 40cm, 50cm, 60cm, 70cm, and 80cm.

Measurements will be taken on the ammeter when the crocodile clip is fixed at between 10cm and 80cm from the permanently connected end.

Each measurement will be taken 3 times and an average current reading calculated. I will then be able to work out the resistance using the equation V=I x R

The circuit will only be connected to the power pack for the duration of the test. The circuit will be disconnected at the end of the test.

To make this a fair test I am only going to change the length of wire, my key factor.

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Conclusion

The results could be more accurate with the following changes:

        We should allow more time for the ammeter to settle

The crocodile clip could be placed more precisely on each 10cm mark.

We could cut up the wire and clipped the wire on the ends. This would give a more accurate reading.

Looking at the graph of amps v length of wire it is possible to fit a smooth curve through the results. Also on the ohms v length of wire a straight line can be drawn between the points with very little scatter. From these two graphs I can assume that a reasonable conclusion can be drawn because the results are reasonably accurate.

To improve the accuracy of the experiment further, I could use a perfectly straight piece of wire and I could also use a pure piece of metal instead of an alloy because of the variations in the composition of alloys. I could also use better technology to measure the Resistance for example I could use a more accurate ammeter that gives a better reading to more decimal places.

I would then take several; possibly five readings, letting the wire cool down completely before reading the next result. This would make it more of a fair test, as there are a greater number of readings to take an average from. I would work out the averages and record them.

 In the physics textbook by Jim Breithaupt unit B ‘resistance’ page 73 quotes in a summary that the resistance of a wire is proportional to its length.

...read more.

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