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Factors affecting resistance (R) of a wire

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Factors affecting resistance (R) of a wire

Introduction                                                                                                        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. The unit of resistance is the ohm and the symbol for ohms in electric circuits is the Greek letter omega, Ω. 1 ohm is the amount of resistance that limits the passage of current to one ampere when a voltage of one volt is applied to it.

Resistance occurs when the electrons travelling along the wire collide with the atoms of the wire. These collisions slow down the flow of electrons causing resistance. Resistance is a measure of how hard it is to move the electrons through the wire.

The basic law of current flow is ohm’s law. Ohm’s law was named after its discoverer George Ohm (1787-1854) a German physicist who researched electrical current in circuits.  George Ohm discovered that the amount of current flowing through a circuit is directly proportional to the electromotive force (volts) impressed on the circuit. Also it is inversely proportional to the total resistance of the circuit. George Ohm also discovered that the circuit also resists the flow of electricity.

George Ohm discovered a rule for working out the voltage of a circuit:

V = I R

V = volts

I = current

R = resistance

This formula can be rearranged to find the current or resistance by dividing the voltage by the known factor.

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Make sure the mains to the power supply is switched off when removing the wire from the circuit to be measured.

Fair test

In order for this experiment be fair, I must take repeats. I will read the ammeter and voltmeter carefully. The room temperature must also be kept constant.  I will use the same ammeter, voltmeter, and power pack, throughout the experiment. To get accurate results I will use a digital ammeter and voltmeter. The voltage going through the circuit will be kept the same every time. Also, the same wire will be used every time so that the material of the wire remains the same.

In this experiment two factors will be changed – the length and thickness of the wire. I will perform an investigation on each variable one at a time, so I don’t get mixed up with the variables. All other factors will be kept the same. These precautions will make my final results more reliable and keep anomalies at a minimum to make the entire investigation more successful.


The following apparatus will be used in the experiment.

  • Power supply
  • 7 Wires
  • Ammeter
  • Voltmeter
  • Wire cutter
  • Variable resistor
  • 2 crocodile clips


First, the power pack was set up with wires leading out of it. The power pack was set as 4v and was at a direct current supply. The wire was connected to an ammeter and then to a resistor by crocodile clips.

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Most errors in our experiment were encountered in the measuring of the wire. This is because it simply was not very practical to hold a piece of wire straight, whilst holding it next to a ruler and then trying to accurately fix crocodile clips to the right part on the wire. Also I do not feel that the crocodile clips were always fixed securely to the wire with a good connection. This also meant that they were easy to move about on the wire changing the length of it. Errors rarely occurred in the setting of the current and the reading of the voltage. Another example of this is the wire was never totally straight when we started the experiment, which may also affect the resistance of it

I do not think that doing any more results in our experiment would have made it any more accurate. I feel that the only way to make it more accurate would be to use a different method – perhaps were we had a bar that did not bend in place of the wire. We could even use a rheostat in place of the wire, because it is essentially a long coiled wire that is connected at different lengths to change the resistance of the circuit.

The results would then have been more reliable and would definitely produce better results, however the results in this experiment are fairly reliable and they did support my prediction. So all in all I think this was a good experiment and best that could have been done with the time and resources available.

...read more.

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