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Investigating how the length of a wire affects the resistance of a wire.

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An Investigation Studying the Effect of Length on the Resistance of a Wire


Investigating how the length of a wire affects the resistance of a wire

Background Theory:

During the 1820`s. the German Physicist; George Ohm investigated the resistance of different metals. The unit we now use for resistance is the ohm, in honor of him.

Ohm showed that doubling the voltage doubles the current. Trebles the voltage will treble the current and so on. The larger the resistance, the greater the voltage needed to push each ampere of current through it.

The voltage in a metal conductor is proportional to the current through it, provided the temperature stays constant. Therefore R=V/I.

The current is the flow of negative electrons in a wire. The electrical current is usually measured in amperes (amps). Therefor one ampere equals one coulomb per second.

Voltage can be though of as the pressure pushing charges along a conductor is a measure of how difficult it to push the charges along.

Resistance can be affected by certain factors:

  1. Length: As you increase the length of the constant wire the resistance increases, because the longer the wire the more energy is needed to push the charges or the electrons along the wire. Therefore voltage must be increased and as you increase the voltage the resistance also increases. Because R=V/I (if the current or I is constant).
  2. Thickness
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As we carried out the experiment, we noticed that the wire heated up during the experiment which meant that this was not a fair test a fair test because resistance varies with temperature, and we want only one variable to affect the experiment which is the length of the wire.

To assure that a fair test is done therefore we decided to add a variable resistor in the circuit. The variable resistor keeps the current constant, and since that we have a constant current therefore we will have a constant temperature.


In order to perform a safe experiment, a low voltage of 3V was chosen so that overheating was avoided. Also lengths less than 10cm were not tried, which also helped to avoid overheating.


After setting the apparatus as shown in the diagram and adding in the variable resistor to set the experiment to a constant current to cause the temperature to be also constant, follow those steps:

  1. Set the first crocodile clip lead to the 0cm position on the meter ruler.
  2. Fix the second crocodile clip lead on the 10cm position on the meter ruler.
  3. Turn on power supply or connect batteries.
  4. Set the current to 0.02 amps to get a constant temperature.
  5. Read off voltmeter reading.
  6. Calculate resistance (resistance=voltage/current), and record results
  7. Turn off power supply or disconnect batteries.
  8. Move the second crocodile clip from 10cm to 20cm and repeat experiment again. After finishing each of these experiments move the crocodile clip 10cms up till you get to 80cm.
  9. Make sure you repeat the whole experiment till you think that your results are reliable enough, and then make an average of all your results.


Length (cm)

Current (amps)

Voltage (volts)

Resistance (ohms)

































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I did that because I felt that some of the wires were short, long, thick, or thin. This would affect the experiment by using more than one variable and it would also affect my results negatively.

I think that I had reliable results because both of the sets of results that I got had nearly the same results and my results and graphs show that.

I don’t think I had a problem with the accuracy of the experiment because I used accurate equipment that measured to the nearest 0.01 units.

I could have improved the experiment by using a bigger range of lengths, and I could have done more sets of results to make my results more accurate. Or even I could change the variable from the length of the wire, to the thickness of a wire or even changing the material of the wire. But I have to consider that I have to keep all the other variables constant of I am changing one of them. i.e., if I am changing the thickness of the wire, I have to keep the other two variables constant. So the length has to be the same all through the experiment, and also I have to use the same kind of wire all over the experiment.

...read more.

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