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To Investigate How Length Affects the Resistance of a Length of Wire.

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The aim of my investigation is to investigate how length affects the resistance of a length of wire.


I predict that if the length increases then the resistance will also increase in proportion to the length. I think this because the longer the wire the more atoms and so the more likely the electrons are going to collide with the atoms. Therefore, if the length is doubled and the resistance should double. This is because if the length is doubled the number of atoms will also double resulting in twice the number of collisions slowing the electrons down and increasing the resistance.

Because the length of the wire is only half the length of the wire below there should be half the number of collisions between the electrons and the atoms. The wire below is twice the length of the wire above and so there should be twice the number of atoms resulting in twice as many collisions and a predicted doubling of the resistance.


What is resistance?

Resistance is the force, which opposes the flow of an electric current around a circuit so that energy is required to push the charged particles around the circuit. Resistance is measured in ohms.

...read more.


Voltmeter: to measure the voltageAmmeter: to measure the currentG clamps: to hold the clamp stands to the tableCrocodile clips and connecting wires: to connect everything togetherPower pack: to supply electricity to the circuitLabels: to mark the intervalsVariable resistor: to have better control over the current.


  1. Temperature: If the wire is heated up the atoms in the wire will start to vibrate because of their increase in energy. This causes more collisions between the electrons and the atoms as the atoms are moving into the path of the electrons. This increase in collisions means that there will be an increase in resistance.
  1. Material: The type of material will affect the amount of free electrons which are able to flow through the wire. The number of electrons depends on the amount of electrons in the outer energy  shell of the atoms , so if there are more or larger atoms then there must be more electrons available. If the material has a high number of atoms there will be high number of electrons causing a lower resistance because of the increase in the number of electrons. In addition, if the atoms in the material are closely packed then the electrons will have more frequent collisions and the resistance will increase.
  1. Wire length: If the length of the wire is increased then the resistance will also increase as the electrons will have a longer distance to travel and so more collisions will occur. Due to this the length increase should be proportional to the resistance increase.
  1. Wire width: If the wires width is increased the resistance will decrease. This is because of the  increase in the space for the electrons to travel through. Due to this increased space between the atoms there should be less collisions.

Method: -

I set up the circuit as shown in the diagram that I have drawn.















I made sure that the wire was carefully tightened at both terminals to try to minimise the kinks or twists in the wire. I then switched on the power pack supply and adjusted the variable resistor until a constant current of 0.4A was flowing through the circuit. I then recorded the corresponding voltage reading that was displayed on the digital voltmeter. I repeated this procedure using different lengths ranging from 50-350cm and adjusting the variable resistor until 0.4A was flowing through the circuit. After recording the corresponding voltage readings for each length and tabulating them I decided to repeat the whole experiment again another 5 times so that I could take the average voltmeter reading for each length.

Variables in the experiment: -

  • In this experiment I varied the length of the wire each time using a range of lengths from 0-250cm.
  • I kept the current flowing through the circuit constant using a variable resistor which I kept varying for each length of wire so that the ammeter would always read 0.4 A. I then recorded the voltage readings from the voltmeter which corresponded to the length of the wire being used.
  • The temperature of the wires in the circuit needed to be kept constant to prevent the whole circuit from overheating. I managed to do this by quickly switching off the power pack supply every time I had recorded my set of readings. I then left the power pack to rest for a small interval of time before switching it on again to record the next set of readings.
  • I also kept the diameter of the wire constant by using the same piece of wire throughout the whole experiment.
...read more.


  • To be more accurate with my results I would place the metre rule directly under the wire, so therefore it would be measured easier and therefore making the lengths more precise.
  • To also improve on my results I could use a new or higher quality digital voltmeter.
  • The next modification I would make would be to use pointers instead of crocodile clips to attach to the wire; I would do this because pointers would be more accurate. The pointers would be more accurate because the tips have a much smaller area than the crocodile clips giving a more accurate measurement of the length of wire.
  • I would also use a newer metre rule.
  • Sometimes the ammeters flicked between a decimal point, I maybe could have thought it was the wrong number and therefore would have ended up with the wrong average resistance.
  • In this experiment, I did not control the room temperature but instead just assumed it was keep constant throughout my experiment; this could have made the wire get hotter and therefore making my experiment not as accurate. In future experiments I would control this variable factor and make it a constant factor.
  • As well as making these modifications, I could also expand on my investigation by testing the same wire but different widths of that wire. I would do this if I had more time to complete it.

Shariar Hime                

...read more.

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