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How the Length of a Wire Affects Resistance

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The main aim of this investigation is to observe how the resistance is affected as the length of the wire in the circuit changes. The variable for this experiment will be the wire itself. I aim to find the resistance simply by changing the length of the wire where the voltage reading will be taken in parallel to the circuit. The voltage readings will be taken in parallel to the circuit where the variable piece of wire will be. This will eventually give the resistance of the variable piece of wire. The length will be steadily changed by 10cm each time. By finding the voltage of the variable piece of wire, and the current across the circuit will enable me to work out the resistance.

To get the most reliable results, everything else as part of the circuit and investigation must be controlled and kept constant. The type of material used in the experiment must be kept constant using the same material and preferably, exactly the same piece of wire. This must be kept constant because often different materials have different resistances. The type of material that will be used will be decided upon by preliminary tests that will be taken.

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After performing preliminary work to find the most suitable material for the main experiment, and the most suitable thickness for the main experiment, I have decided to use thin constantan for the main experiment. This is because this combination gave the largest range of results and other materials contained many more anomalies.

To ensure safety the main thing is to use dry hands when handling anything electrical. Also, you shouldn’t keep the equipment on for too long; this is because it can cause energy loss which will also give unreliable results.

The diagram of the circuit below shows the full experiment that is going to be taking place. image01.pngimage05.png

The red line represents the variable piece of thin constantan. The crocodile clips are represented by black boxes. The voltmeter is set up in parallel to the circuit and the ammeter is set up in series inside the circuit.


  1. Draw a table to collect the raw data, i.e. the length of wire in the circuit, the voltage and current.
  2. Set up the circuit as shown in the diagram above.
  3. Start with 100cm of thin constantan and record the results of the current and voltage readings shown on their respective instruments.
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The results that were obtained from the main experiment can definitely be used to make a firm conclusion from. The line of best fit and the numerical data can be used as evidence to support the predication made by myself in the planning section. I predicted that the resistance would be directly proportional to the length of the wire, and this is shown by the line of best fit. The theory that I stated in the conclusion is also supported by the graph and its line of best fit.

I think that doing three more repeats was enough to obtain satisfactory and reliable enough results. I would not say that doing more repeats would get more reliable results. Instead, I think that maybe, in place of using wire that easily bended and caused disruptions to the results, maybe a bar would have worked better and more efficiently. This would have got more reliable results.

Hinesh Mehta

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