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The Factors Affecting The Resistance Of A Wire

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Samir Khan 4S2        Factors Affecting Resistance Of A Wire

Mr. Kerr

The Factors Affecting The Resistance Of A Wire


Aim: - The aim of this investigation is to investigate what effects different factors have on the resistance of a wire.The investigation will determine what effects the factor we choose has on the resistance of a wire.  

Variables and Key Variables: - There are many possible independent variables that could be changed in order to affect the dependant variable.  The dependant variable in this experiment is that of resistance.  This means that resistance will not be changed or controlled during the resistance but the independent variable will be used to change it.  I came up with many initial ideas for things that could be used as the dependant variable in my investigation.  These include: -

  • Length
  • Width- Diameter/Cross-Section
  • Current
  • Voltage
  • Temperature
  • Material
  • Room Temperature
  • Age Of Wire
  • Humidity
  • Light
  • Pressure
  • Magnetism

Preliminary Work: - In order to find out the best variable to investigate with regard to what affect it has on resistance a number of preliminary tests had to be carried out.  The aim of these small-scale experiments was to see which of the possible dependant variables have an effect and then to find out which of them would be best to investigate.  Some possible variables had to be ruled out from the start.

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: - The next decision I was required to make was to select the best wire to use for my investigation out of those available.  In order to find this I had to experiment using different wires in order to see which one with which thickness is the best to use.  For the first part, in order to find out which thickness to use, I decided to select a wire to use.  I decided to use Constantan simply because it had the greatest range of wires.  I decided to observe the resistances of the same material of wire using different thickness.  This was done by connecting the wire to an ohmmeter and observing the resistances.  The wire was connected using crocodile clips and the length of these crocodile clips apart from each other was how I measured the length.  A metre rule was placed next to it in order to ensure accuracy.

Diameter 0.914cm

Length (cm)








Diameter 0.152cm

Length (cm)








From these results in the preliminary experiment it is obvious that the greater the width the greater the resistance and therefore the greater the range of resistances in our results.  Therefore from this experiment I conclude that I decided to use diameter 0.152cm for the main investigation.

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I will now explain scientifically why certain variables must be kept the same throughout the investigation.  The temperature must be kept the same as when you raise the temperature more atoms vibrate and this impedes the passage of free electrons.  Thickness of the wire must be kept the same as if you vary this you also vary the amount of room electrons have to manoeuvre.  Finally the current must also be kept constant because as this increases so does the temperature of the wire.  All these precautions must be taken in order to ensure that the data obtained is as accurate as possible as well as being reliable.

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