How well do different samples of Constantan wire conduct electricity?

Apparatus List:

• Power supply unit (PSU)
• Connecting leads
• Constantan wire
• Crocodile clips
• Meter rule
• Voltmeter
• Ammeter

Variables:

• Length of Constantan:  20cm, 40cm, 60cm, 80cm, 100cm.

Method:

• Set up circuit as shown below:

• Prepare each of the 5 lengths of wire by measuring them to the required length using the meter rule.
• Attach both ends of the first length to the circuit using crocodile clips.
• Switch on the PSU.
• Take readings from the ammeter and voltmeter after the display reading has settled.
• Switch off PSU and replace length of Constantan with a different length.
• Then repeat the procedure outlined above for the rest of the lengths.
• Repeat the whole experiment a further 3 times and take an average reading for each length of Constantan wire.

Safety:

• Constantan wire will become very hot if left connected to the circuit for longer then necessary.
• Make sure that all the wires are connected securely into the correct terminals and that there us no bare wire (except the length of Constantan).

Constants:

• Ammeter
• Voltmeter
• PSU
• Thickness of Constantan (0.3mm)
• Voltage

Analysis

• From my results for the original experiment and the three repeats I calculated the resistance for each length in each experiment by using the formula:

Resistance  =   Voltage

   Current

• I then took an average voltage, current and resistance for each length.
• Using these average results I plotted a graph and upon it, drew a line of best fit.

• The graph shows a very strong positive correlation, with a straight line of best fit passing through the origin; indicating that as the length of the

Constantan wire increases, the resistance increases proportionally.

• This fully agrees with my prediction in my planning stage.

• As the length of the wire increases the electrons flowing round the circuit have a further distance to travel through the Constantan wire.

• This wire contains atoms and as the electrons flow through the Constantan wire, some of them collide with these atoms.
• Therefore, as you increase the length of the wire, you increase the number of collisions.
• These collisions determine the resistance, i.e. more collisions equals more resistance (resistance is defined as the opposition to the flow of charge).
• Finally, if you triple the length of the wire you should triple the amount of resistance generated. This is because if you have three times the length of wire; you have three times the amount of atoms within the wire. Hence, the electrons flowing through the wire are three times more likely to collide with an atom, therefore generating three times the amount of resistance.
• An example from my experiment:

a)  Resistance for 20cm = 1.30 Ohms

b)  Resistance for 60cm = 3.77 Ohms

According to my conclusion, if we multiply a) by 3 it should equal b)

1.30 Ohms x 3 = 3.90 Ohms

• There is a difference of 0.13 Ohms between the predicted and the actual readings (this could be because I took the original readings from the averages of all four experiments)

Evaluation

• I believe my experiment was very successful.
• There were no major anomalies in any of the experiments which can be seen in the results table and by the correlation of the points on the graph
• The few very minor anomalies that there may have been were irrelevant because an average was taken.
• The readings were all done digitally from the ammeter and voltmeter so human error is not an influence here.
• There is room for human error in other aspects of the experiment however; the length of the wire may not be accurately measured as it is hard to measure to the nearest millimetre or less using only your eye and the wire is not always flat. Also the crocodile clips may not have been exactly at the end of the wire etc. But this however should not produce any major anomalies, which it did not.
• The reason for the slight variation in results between experiments may be down to the different voltmeters, ammeters, leads and power supply units used.
• I believe that the evidence I obtained during this investigation is sufficiently strong and reliable enough, to support my conclusions stated earlier.
• I believe that this procedure was excellent and produces very accurate results.

• To simply further the experiment you could use a greater variety of lengths of wire confirming the conclusions made.

• To further the experiment more so, I would compare how the length of wires made from different materials effects the resistance using the same experiment as this one. Materials such as copper, nickel and brass could be used.
• You could also measure thickness of wire instead of length, or how the temperature of the wire effects the resistance.