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An Investigation into how the Length of the wire affects its resistance

Extracts from this document...


Jenny Arbuthnot

Physics Coursework

Aim:  An Investigation into how the Length of the wire affects its resistance


Resistance is a measure of how hard it is for an electrical current to flow through a conductor.  In a metal, current flows through the wire when a voltage is applied across the ends of the wire.  The current is free electrons flowing because one end of the wire is made positive.  The resistance will vary depending upon how easily the electrons flow through the wire.  The more difficult the electrons find it to flow through the wire, the higher the resistance will be.  Therefore, resistance can be thought of as how much energy is lost by an electron as it moves along a wire.

The resistance through a wire can be measured using the following equation, providing that the voltage and current passing through the component is known:

Resistance= potential difference (voltage) across a component

                Current through the component


A Diagram showing the free electrons and positive ions inside a wire while a current is flowing.

Inside a metal wire, there is a regular array of positive ions.  There are also free electrons which travel in between the positive ions like gas molecules, so when a voltage is applied across the ends of the wire, the negative electrons are attracted towards the positive end of the wire and thus a current flows.

Wires have resistance because electrons cannot travel smoothly along it without bumping into the positive ions.

...read more.


8 Crocodile clips with good contacts or the resistance will be affected.  Crocodile clips secure the electrical wires to the components.

A Preliminary Experiment:

In this experiment, I am going to set up the following circuit in order to find out which lengths of wire and what current I am going to use in the main investigation.  This is how I am going to set it up:


  I am using the variable resistor to make sure that the current within the circuit remains the same, even when the length of the wire changes.  In this experiment I am expecting to find out:

  • How much voltage the power pack should be set to in order for good results to be achieved but at the same time make sure that the wire does not overheat.
  • The different lengths of wire I should use in order for the difference between the results to be substantial enough to draw a graph that is easy to read.

Results of the preliminary experiment:

See handwritten sheet.

Method for the main investigation:

  • Set up the equipment as shown in the diagram below:


  • I am going to make sure that there is a good connection between the components and the circuit.
  • I am going to make sure that all the components work (i.e. the voltmeter, ammeter and variable resistor) by firstly adding a bulb to the circuit.
  • I am going to measure the lengths along the wire using a ruler.
...read more.


  • I believe that as there were no anomalous results and the results were as I had predicted, the results are sufficient to be able to draw the conclusion that length and resistance are directly proportional.  If I had more time, I could check if the results were completely accurate by repeating the experiment again and making sure that I could reproduce the same results again.
  • If I were to carry on with this investigation and to explore resistance further, I would find the resistance of more lengths and I would try using more than just three currents.  This expansion of my investigation would support my results further.  Also, I would repeat the currents and the lengths that I did again to make sure that I could get the same results, which would support my conclusion of this investigation.
  • If I could improve on this investigation, I would change the type of ammeter and voltmeter that I used so that it would give a reading of more than two decimal places.  This would help give more accurate results.

Reference Books Used:

I used the following books in order to help me find the scientific knowledge:

  • ‘Physics for You’ by Keith Johnson
  • ‘Complete Physics’ by Stephen Pople

...read more.

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