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Investigation on how the potential difference between the ends of a wire would depend on the length.

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Physics AT1 - Metal Wires

Investigation on how the potential difference between the ends of a wire would depend on the length



A Cimage01.png


The diagram shows two wires AB and BC

connected together at B and connected directly                                                                 to the terminals of a cell at A and C.                    



In this investigation, the potential difference between points B and C will be studied to see how it depends on the length of the wire BC. It is also shown that the wire BC is of a different material which will also be considered in the investigation.

Potential difference (V) is the difference between the potentials at two separate places of a circuit.

Electricity is conducted through a conductor, in this case wire, by means of free electrons. The number of free electrons depends on the material and more free electrons means a better conductor, i.e. it has less resistance. For example, gold has more free electrons than iron and, as a result, it is a better conductor. The free electrons are given energy and as a result move and collide with neighbouring free electrons. This happens across the length of the wire and thus electricity is conducted. Resistance is the result of energy loss as heat. It involves collisions between the free electrons and the fixed particles of the metal, other free electrons and impurities. These collisions convert some of the energy that the free electrons are carrying into heat.

...read more.


Other values that could be measured in a normal circuit cannot be measured in this circuit. For example, current cannot be measured as the ammeter cannot be connected directly in series. Therefore resistance cannot be measured.

List of Apparatus

  • Battery
  • 2 wires of different material
  • 2 leads
  • Voltmeter

Circuit Diagram

A            Cimage00.pngimage03.pngimage09.pngimage02.png





Obtaining Evidence


  1. First attach the two metal wires to the two terminals of the cell. Points A and C.
  2. Then they must be attached directly at point B.
  3. Two leads must be connected to the wire BC using crocodile clips. One lead connecting to C and the other connecting to B. Both these leads must be connected to the voltmeter so it is in parallel.
  4. Then the voltage measurements must be recorded.
  5. The length of the wire BC is varied by pulling it through the battery terminals.
  6. Each value was measured and recorded in a table.
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The graph shows that my results were very accurate. This is shown because there is very little scatter and the anomalous results are still very close to the line. This is because many precautions were taken so it was a fair test. It is mainly because the results were recorded accurately and not rushed as it took quite a long time for the readings on the voltmeter to settle. Also any anomalous results occurring on the graph could have been caused by the measurements of the wire not being as accurate as hoped because the wire was tangled and difficult to measure with a straight ruler. A way to improve this may have been to put heavy loads at the end of the stretched wire so it would remain straight and would be easier to measure. Also the wires may have been overheated, which could have affected the results because hotter wires have more resistance. To improve this, the temperature of the wire must be kept constant. One way that this could be done is to coat the metal wires with an insulating material. This would have allowed the wires to remain at a constant temperature and resistance would not be affected, therefore the potential difference will not be affected.

I am fairly pleased with my results and the method used was appropriate as I took more than one result and found the average, which made my experiment successful. But it could be improved as more results could have been taken to improve the accuracy.

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