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The Resistance of Lengths of Wire.

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James Bell 11.1

Plan for Science Course Work

The Resistance of Lengths of Wire


To investigate the resistance of different lengths of wire and to look for a correlation between the length of the wire and it’s resistance.


Ohm is the common unit of electrical resistance, equivalent to one volt per ampere and represented by the capital Greek letter omega. The resistance of a wire is directly proportional to its length and inversely proportional to its cross-sectional area. Resistance also depends on the material of the conductor. The resistance of a conductor, or circuit element, generally increases with increasing temperature. When cooled to extremely low temperatures, some conductors have zero resistance.

        The Greeks discovered electricity over 2000 years ago, and electrons were discovered by J.J Thompson in 1844.


I will test different lengths of wire by inserting it into the circuit shown below and record the readings of the ammeter in a table.  I will then calculate the resistance by dividing the potential difference, which is the number of joules transferred per coulomb (measured in volts), by the current, coulombs per second (measured in amps) of the circuit to give me the resistance in ohms.  Resistance limits how easily an electric current can flow through a substance.

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        I shall be using a low voltage so that the wire does not get too hot.  This heat energy in transferred from the kinetic energy of the free electrons when they collide with atoms in the metal.  The kinetic energy is dissipated through the metal in vibrations which generate heat due to friction.  This should reduce any feedback resistance generated by heat of the wire generated by the resistance created by the wire itself.

        I have found from prior research and experimentation that if I were testing different widths of wire, the thinner ones would have more resistance.  If I were experimenting with types of metal, gold silver and copper in that order would have the least resistance.        


All the connecting wires will be insulated to prevent shocks or short circuits.  I will be using a low voltage so that the test wire does not get too hot and to lessen the possibility of damage from an electric shock.

        I will not touch any electrical equipment with wet hands and I understand what to do in the event of someone receiving an electric shock.  There is also a carbon dioxide fire extinguisher in the laboratory in case of an electrical fire.


Power pack, red and black insulated wires, two crocodile clips, volt meter, ammeter and 3 lengths of constantan 24 swg wire,


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        Without the opportunity to re-take my results or measure the overall effect of measuring the potential difference of the whole circuit instead of just that across my wire I have to use what results I have.  Unfortunately no one else in the class carried out the same experiment as myself, so I am unable to compare my results.

        I think that due to the unprecise nature or needle based meters and the problem of the heat and resistance problem it would be very difficult, if not impossible to find any precise formulas for calculating resistance from wire length.

        If I were to repeat this experiment I would like to use precise, digital ,electronic volt and ammeters.  I would also like to measure the temperature of the wire, and keep it at a constant temperature by refrigeration.

        I would also correct my placement of the voltmeter.  I would like to expand my experiment to look the other variables, change the voltage, type and width of wire.


Microsoft Encarta 95 CD ROM

The On-line Britanica Encyclopaedia

Co-ordinated Science 2    Edited by Ken Dobson & Chris Sunley

GCSE Double Science Physics The Revision guide (Higher Level) Edited by Richard Parsons

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