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

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Aim: 

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:

Calculations:

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:

 Cautions were taken in connecting the circuit, because the Voltmeter had to be in parallel and the ammeter had to be placed in series. The various different wires were tested on two measurements and the results were recorded in a table.

Results for Preliminary Testing:

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.

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Prediction: 

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. If a wires length is longer then the electrons will have to gather together for a greater period of time to pass through a wire then they do in order to pass through a short wire that’s why there is greater resistance in a longer wire. So if the length is doubled the resistance should also double. This is because if the ...

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