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We are going to carry out an experiment to test the resistance of a piece of wire.

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Kate Parkin


An Experiment to Test the Electrical Resistance of a Piece of Wire and How it Changes with Length


We are going to carry out an experiment to test the resistance of a piece of wire.

Scientific Background

A piece of wire has electrons in it. Electricity also has electrons in it. Therefore when you try and pass electricity through a piece of wire the like charges (Electrons) repel against each other causing resistance which can be measured in Ohms.


Ohm’s law says that the Resistance offered by a piece of wire is directly proportional to the length of the wire, i.e. given the same potential difference the current will decrease at the same rate as the length of wire increases. The formulae for this states that resistance = voltage (potential difference) / current.

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  1. Power pack
  2. Ammeter
  3. Variable resistor
  4. Voltmeter
  5. A Roll of wire



  1. I will set up my apparatus as shown in the diagram
  2. I will measure the wire to 90 cm and attach the crocodile clips to it
  3. I will set the volt meter to a voltage of 0.5 Ohm
  4. I will record the current off the ammeter and write the answer in the table
  5. I will repeat these steps for a voltage of
  1. 1 Volts
  2. 1.5 Volts
  3. 2 Volts
  4. 2.5 Volts
  5. I will record the current for these volts and write the answers in the table
  6. I will repeat these steps for a length of
  1. 80cm’s
  2. 70cm’s
  3. 60cm’s
  4. 50cm’s
  5. 40cm’s
  6. 30cm’s


To work out what the resistance is for the piece of wire I added all the combined averages (see table on last page) together and divided it by 90+80+70+60+50+40+30.

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My results also showed that when you increase the voltage the current also increases but the resistance stays the same. For instance, in the 90cm length of wire a potential difference of 0.5 volts gave a current of 0.08 amps and a resistance of 6.25 ohms whilst at a potential difference of 2.5 volts the current rose to 0.37 amps but the resistance remained at 6.7 ohms.


I decided to take the measurements three different times and use the average to plot the graphs because we thought that this was the best way of getting definite accurate results without using up all our time. We found the average by taking the mode instead of the mean because it ensured that anomalous results.

Anomalous results could have happened if the temperature of the wire had risen or the components were moved.

...read more.

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