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A Factor which affects the resistance of Constantan Wire.

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Ross Bowden 11RCB

Physics Coursework

A Factor which affects the resistance of Constantan Wire


I am going to carry out an investigation to see what will happen to the resistance of Constantan Wire when I vary the lengths of various diameters of the wire.

To ensure that this is a fair test, providing that it is possible, I will measure the resistance of the wire at the same lengths each time. I will also use the same apparatus and try my best to ensure that there are no kinks or creases in the wire.

The surrounding temperature will be kept constant while the experiment is being conducted because the particles in the wire will move faster when it is hotter and this will therefore have an effect on the resistance. I will do this by doing the experiment in the same room at the same time.                                                          The moister in the air must be kept constant because it will moisten the wire and electricity will pass through the metal quicker. I will do this by conducting the experiment in the same place at the same time.

For my preliminary work, I will see how short I can have a piece of wire which will give me an ammeter reading of 1amp or less.

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Resistance involves collisions between the free electrons and the fixed particles of the atoms in the metal. These collisions loose energy and time and therefore resistance occurs. As the resistance of a material increases so must the force required to push the same amount of current through the metal. Ohms law is defined by this equation: Resistance, in ohms (Ω), equal to the Voltage, in volts (V) divided by the current, in amperes (A).

I predict that the resistance will increase proportionally as the length of wire increases. If I double the length, the resistance will double. I say this because in a certain length of wire, electrons have to negotiate their way through a collection of ions. If you then double that certain length of wire, the electrons have to negotiate their way through twice as many ions therefore doubling the resistance of the length of wire. This is shown in my free-electron model below. To quantify my prediction, I will give a simple example. If I have a length of wire 50cm, with a

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4. Kinks in the wire.

All the reasons stated above are acceptable but 4 is the most likely one because all the other results in the other wires were close or on the line of best fit, which would mean that the problem would have to have been within that certain section of the investigation.


I think that my evidence is accurate because nearly all of the points on my graph tough their respective lines of best fit. Heat, apparatus or kinks could have affected the points that strayed off the line, but they were only minor deviances, not enough to be considered anomalies.


Most errors in my experiment were encountered in the measuring of the wire. This is because it was hard to keep the piece of wire straight and measure it with a 1m ruler and then fixing crocodile clips to the designated part on the wire. Also I do not feel that the crocodile clips were always fixed securely to the wire with a good connection.

My Method and Improvements

I think that my method was completely suitable for this investigation. The only improvements I can think of is to give us some more time to allow us to do some repeats to ensure reliable results and prevent anomalies and also to give us a device that we can use to hold the wire taught to ensure accuracy.

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