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Investigation into how the resistance of a wire depends on its length.

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Investigation into how the resistance of a wire depends on its length.


image00.png        My independent variable will be the length of wire.

image00.png        My dependant variable will be the resistance of the wire, found by measuring the voltage (volts – V) and the current (amps – I) and using the following formula: -

V = R


image00.png        My controlled variable will be the area of the wire, which I will keep the same as far as is realistically possible.


Resistance occurs because as electrons pass along a wire they collide with atoms of the metal and so lose energy. In a longer wire there will be more collisions and so the electrons will lose even more energy.

I predict that the longer the wire is the more resistance there will be.  I believe this will be the case as over a longer distance resistance will have more of a chance to build up, whereas over a short distance the resistance will not have such a chance, and there will be less resistance as a result.  I must keep the area of the wire the same as far as possible

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Preliminary Results: -

Measurement (cm)

Ammeter (A)

Voltmeter (V)

Resistance (Ω)













I have found from the trial run that three more items are necessary to this experiment and should therefore be added to the apparatus list.  Two are for safety purposes.  They are: -

Cellotape and several drawing pins to secure loose wires to prevent the risk of burning if the live and insulated wires come into contact.

The final one is for convenience.  As we are measuring the resistance at regular intervals of 10cm, a meter rule is inappropriate for measuring.  Therefore, we will employ a conventional 15cm ruler.

Revised method.

  1. I will firstly measure out 126cm constantan wire using the meter rule.
  2. The circuit will then be set up as previously shown, with the wire pinned down to avoid any accidents.
  3. I will mark on all our lengths, 23 –125 cm at intervals of 10cm, using the permanent marker and the 15cm ruler.
  4. I will secure one crocodile clip to the board using cellotape, and use it to hold the end of the wire.
  5. The other I will clip onto the wire at 25cm.
  6. Having made sure
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Using different types of wire in the same experiment to test the theory behind this experiment further would further prove whether or not the theory is true.

Further research has shown that in the metal alloy “constantan,” the resistivity (the electrical resistance of a conductor of particular area and length) of this alloy is not affected by temperature. Therefore, in these experiments Ohm’s Law does not apply.


The following Websites were useful sources of information in the writing of this investigation: -

image00.pngChannel 4: Homework High – Science





99707.doc                02/05/07        Alison Kemble 11S.

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