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To investigate different resistance's of wires in order to solve 'The Lamp Problem'.

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To investigate different resistance’s of wires in order to solve ‘The Lamp Problem’.

Introduction to the task:

  1. Carry out experiments to investigate factors affecting the electrical resistance of different wires. Make measurements to include resistance up to about 12-15 Ohms.
  1. Use results of the investigation to solve ‘The Lamp Problem’.

The Lamp Problem:

A lamp has a resistance of four Ohms and can take a maximum of 1 Amp. Unfortunately, the only battery available has a potential difference of 12 Volts, which would blow the lamp.

A resistor can be connected in series with the lamp so that the maximum current is 1 Amp.

Circuit Diagram of the lamp problem:


The resistance needed in order to solve the lamp problem is 8 Ohms as four Ohms is taken up by the lamp and hence we need another 8 Ohms so the voltage does not blow the lamp.

The working can be shown as:

Volts/amps = resistance

12/1= 12 Ohms

12- 4(The lamps resistance) = 8 Ohms

Preliminary Method:

In the preliminary testing, I will use different lengths of wires to measure their resistance. The main idea of doing this is to find a suitable wire, which I can do my main testing on, as I will need a wire, which doesn’t have such a low current I will need a huge amount of length to increase the resistance. I also wanted to become more familiar with the experiment for the main testing. Also if I had any problems I could correct them for the main testing. This would enable me to achieve I believe better results for the main course of the investigation.

Firstly, the circuit was set up as shown below:

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Bar graph of preliminary results showing the different materials with varying lengths:

From these results I have chosen to use 0.23mm constantin for the wire I am going to test in my main experiment. I have chosen this wire as it has the highest resistance and so I will be able to get a good range of readings for the varying lengths.

Main investigation:

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

Factors affecting resistance:

  1. Diameter of wire
  2. Length of wire
  3. Temperature at which wire is kept
  4. The material of  the wire
  5. The potential difference or voltage.
  6. Voltage across circuit
  7. Cross sectional area.

I am going to keep some of these factors constant but I will vary the diameter and length of the wire as well as the material for the first part of the investigation to see which wire would be most suitable to fit the lamp problem. This will be part of my preliminary work after that I will choose a wire to carry out my investigation on as I will be able to have a rough idea from the preliminary work which wire will be most suitable because some values maybe to high or to low.


I believe that:

The greater the length of the wire the greater the resistance as there are more atoms and therefore there is a greater opportunity for electrons to collide and hence the greater resistance.

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If I could have had a more precise measuring tool for measuring the wire this could have possibly given me more reliable results as I do not believe that the measurements of length I took were exact and this could have effected the resistance that I obtained for certain results. A way in which I could have tackled the problem was to place two points on the wire and then cut these points at either end using an electronic saw this would have given me more precise measurements. I also think the investigation could have been made more accurate if the wire was perfectly straight as the wires which I clipped onto the crocodile clips were often bent and had kinks in them, I feel this could have slightly altered the resistance. If I had a machine to straighten the wire then I think I would have possibly got more reliable results.

I believe that my investigation was successful as I did manage to complete all tasks set. I also feel that the results I took were sufficient to provide proof for my conclusions as I had enough results to draw a descent line graph from and then later analyse. I also was able to make relevant comments on my results and I was able to see patterns and trends, which lied in them.


Mohammud Malik

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