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An Experiment To Investigate How The Length Of A Wire Affects The Resistance

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To find out how the length of the wire affects the resistance.


To make current flow through a conductor, there must be a potential difference (voltage) across it. Copper connecting wire is a good conductor and a current passes through it easily. However, a similar piece of nichrome wire is not so good and less current flows for the same PD. This is because the nichrome wire has more resistance than the copper wire. A basic definition of the term resistance is anything in the circuit that slows the flow down. So, resistance is the ability of an object to resist the flow of currant.

Resistance is calculated using the equation:

RESISTANCE (Ω) =    PD across conductor (V) xx

                       Current through conductor (I)

The SI unit of resistance is the ohm. Its symbol is Ω. (The symbol Ω is the Greek letter omega). The resistance equation was stated in ohms law.

This diagram shows how the equation is compiled:


In a circuit there is always a balance between the voltage and resistance. The voltage is trying to push the current round the circuit and the resistance is opposing it. The relative sizes of the voltage and resistance decide how big the current will be.

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  • 1 Power Pack
  • 4 Wires
  • 55cm wire on board
  • 2 Crocodile Clips
  • Voltmeter (0-5V) (Low range for more accuracy)
  • Ammeter (0-2A) (Low range for more accuracy)


  1. Attach 1 wire to the power pack and to the ammeter, connect another from the ammeter to the wire on the board.
  2. Attach 1 wire from the power pack to the voltmeter. Connect another wire from the voltmeter and (using a crocodile clip) connect onto the metal on the board at 0cm.
  3. Take a reading from the ammeter and the voltmeter at 0cm, then move to 5cm and take the two readings.
  4. Move the clip and take readings at 0cm, 5cm, 10cm, 15cm, 20cm, 25cm, 30cm, 35cm, 40cm, 45cm, 50cm and 55cm.

Repeat each distance twice to get an average set of results. To find the resistance use the equation: RESISTANCE (Ω) =      PD across conductor (V)

                                                     Current through conductor (I)

  1. Find the average set of results and record them into a table.
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        Inaccuracies to our results could have been caused when clipping the crocodile clip onto the length of wire on the board. If we have misjudged a measurement slightly the value for that length of wire could have been inaccurate as the resistance through that distance could have been increased or decreased. Inaccuracies could also have been caused by an inaccurate and changing supply of power into the circuit we were measuring resistance on.

If we were to do this experiment again, I would increase the number of results we collected. Instead of collecting 11 results and choosing lengths in distances of five we could record smaller intervals of length like every 2cm. This would make our graph more accurate as it would have more points plotted on it. I would also use a more reliable source of power, which is constant throughout the experiment, as this would keep changes in the voltage and therefore the current minute. Further procedures like repeating the experiment for a third or even forth time could improve the accuracy of the results as well.

...read more.

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