An Investigation into the Factors Effecting the Resistance of a Wire

Equipment

Powerpack

Voltmeter

Ammeter

Crocodile clips

Wooden meter rule

Length of wire measuring over 100 cms

Method

I will set up a circuit using the powerpack, crocodile clips and wires. I will then sellotape the 100cm wire to the meter rule and connect the wire to the positive crocodile clip at 0cm on the rule. I will be able to move the negative crocodile clip and attach it every 10cms along the 100cm wire. The voltmeter and the ammeter are connected as shown in diagram A. Care must be taken to make accurate measurements when attaching the negative crocodile clip at 10cms, 20cms, 30cms etc or the results of the experiment will be effected. Each time the negative crocodile clip is attached I will carefully record the ammeter and voltmeter readings. I will use these readings to calculate the resistance. The unit of resistance is the Ohm and I will use Ohms law        V  = R

                                       I  

Diagram A

This shows an ammeter A and a voltmeter V and connected to find the value of resistance                                     

Results

This table shows the affect of length of wire on voltage, current and resistance. The resistance was calculated as follows:

V = R                0.86 = 0.71

I                             1.21

I put these results on to a graph and filled in the line of best fit (see graph A)

Conclusion

The results on the graph support my prediction that the resistance would increase in proportion to the length of wire. For each increase in length there is a proportionate increase in resistance. This is because the amount of atoms that the electrons will have to pass through in the wire will increase in proportion to the length of the wire. The results show that when the length of wire is doubled the amount of resistance is approximately doubled. For example at 20cms the resistance was 1.43 Ohms and at 40cm the resistance was 2.87 Ohms. I would have expected the result at 40cms to be 2.86 Ohms. This only is 0.01Ohms away from a perfect result. This could possibly have been caused by inaccurate measurements when attaching the negative crocodile clip. It is very difficult to measure the wire accurately using a ruler and to be certain that the wire is completely straight. The graph shows one slight anomaly at 90cms. Using the line of best fit I would expect the result to have been 6.50Ohms instead of 6.39Ohms. This may have been due again to inaccurate measurements of the wire or the crocodile clip may have been placed incorrectly causing poor contact. Also this anomaly could have been due to a change in temperature of the wire, possibly due to a pause in the experiment leaving the wire to cool.

  If I were to do this experiment again I would try to use more accurate forms of measurement and take greater care when ensuring that the wire is completely straight when secured. Also, taking readings every 5cms would make my results more detailed and perhaps explain the anomaly better.

 

CHLOE MCGEOWN 11D

PHYSICS COURSEWORK

MR HOGG