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Investigating resistance of resistors in series - What effect, if any, does the length of a wire, have on its resistance?

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 Pilot Study:

Investigating Resistance of Resistors in Series


Circuit A                                                Circuit B


Set up Circuit A according to the diagram.

Set the power pack to a low voltage: it should give a low current around 0.20 A. this is because a high current would cause a resistor to get hot and this will affect the resistance.

Switch on the power pack and record values for the V (voltage) and I (current).

Repeat this twice to ensure the experiment is reliable.

Calculate resistance using Ohm’s Law (R= V/I).

Repeat the procedure for Circuit B.


Circuit A

V (V)

I (A)

Resistance (Ω)










Average Resistance is 5.13 Ω

Circuit B

V (V)

I (A)

Resistance (Ω)










Average Resistance is 11.33 Ω


Using two identical resistors in series gives double the resistance of one. We can see this from the results that show Circuit B to have double the resistance of Circuit A.

Each resistor is made of a fixed (a certain) length of wire, and if we double the number of resistors, it means doubling the length of wire. This doubles the resistance. This suggests the longer the wire, the higher the resistance.

Skill Area P: Planning

What effect, if any, does the length of a wire, have on its resistance?

The purpose of this investigation is to see how the length of wire affects the dependent variable, resistance; by using 9 different lengths of wire, to compare and contrast results to deduce a conclusion, and hopefully prove my prediction correct.


I think that the resistance of the wire is in direct proportion (the relation between two quantities whose graph is a straight line, and if one of the quantities is changed by whatever factor, the other would also change by that factor)

...read more.


  • Length of Wire

This is our key variable, as this is the factor that we are going to change throughout the experiment. By changing the length of the wire, this will have an effect on the resistance, as the two are directly proportional. We measured the length of wire using a meter stick, and applying crocodile clips at correct intervals.

  • Current Supplied

This is a controlled variable, as it is constant throughout the experiment. If we supply more current, this will affect the resistance as resistance is measured by the energy pushing the electrons around the circuit, and the rate of the flow of the electrons, (R=V/I). We will control this variable by carefully reading the ammeter, making sure it is at exactly 0.20 amps, and recording our results.

  • Material

This is also a controlled variable, and we have used 28 SWG NICHROME wire throughout the experiment. This is because different material as have different numbers of free electrons in them, and these free electrons collide with the fixed electrons in them, and the energy lost as a result of these collisions is resistance; so if we changed the material, this would change the number of free electrons, which would change the number of collisions, which subsequently would change the resistance.

  • Voltage

This is our dependent variable as this is the one we will measure so we can calculate voltage, and by using voltage and current (0.20 amps) we can calculate the resistance. If we increase the voltage this will increase the resistance in accordance to Ohm’s Law (R=V/I). We measured the voltage by carefully reading the voltmeter.

  • Temperature

This is also a controlled variable, and at a higher temperature, resistance too is higher.

...read more.


We could use exactly the same procedure and wire (SWG 28 nichrome) as this experiment, however we could use a wider range of wire lengths, till 10m, over intervals of 50 cms. This means that we will be conducting the experiment with a far wider range of wire lengths, to see whether the results we obtain follow our original experiment’s line of best fit. The controlled variable within this experiment will be the current supplied, and we will monitor the voltage using a voltmeter, and use our findings to calculate the resistance if the length of wire. By then plotting a graph of length of wire against resistance, we will be able to see whether there is a pattern between the results, and whether they support our original conclusion.

Another experiment we could conduct is to see whether our conclusion is supported when using different wire materials. We could use the same procedure as our original experiment, but with a different key variable. In this experiment the key variable is the length of wire, as we are constantly changing it; however in a further investigation, our key variable could be types of wire. So we would keep the length, and thickness of the wire constant, however we could change the material from which the wire is made from e.g. Silver/ copper/ nichrome/ constantan etc. We could supply one given current to the length of wire, and by using a volt meter to measure voltage, we can calculate the resistance of the wire, we could then plot the resistance of the wire against the length, and then seeing whether in all materials the length of the wire is still directly proportional to the resistance.

...read more.

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