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Resistance Coursework

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Introduction

Resistance in Wires.

Aim: to investigate how the length of a conducting wire affects the resistance of the wire.

Relevant Scientific Knowledge:

Resistance is something in a circuit, which slows down the flow of the current. It is the measure of the material’s opposition to the flow of electric charge. It is denoted by the symbol ‘R’, and the SI unit is ohm (Ω).

Ohm’s La w: Ohm’s law is named after George Ohm who discovered it. It states that the voltage drop across a resistor is proportional to the current running through it. The formula used to work out the voltage is V=IR

It is easier to set out in the formula triangle: image02.pngimage03.pngimage00.pngimage01.png

The primary causes of resistance in the metal are:

  • Imperfections;
  • Impurities;
  • Electrons colliding with the atoms themselves.

When the temperature of the metal increases the amount of collisions increases, which means the resistance increases. Temperature is a measure of the kinetic energy of particles. Positive ions in the metal gain kinetic energy from electron when collisions occur, and therefore they have larger vibrations. This leads to the frequency of the collisions to increase. This is the heating effect of the current and makes the resistance increase. This effect cannot be avoided but can be limited by controlling the time the current can flow through the wire.

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Middle

0.195

5.12820512821

5.13

28

1

0.18

5.5555555555

5.56

30

1

0.16

6.25

6.25

During this trial run I have found many ways to improve the experiment so that it is fair and gives me better more accurate results.

  • I noticed that the voltage changed each time we changed the lengths, so to make it fair I will use a variable resistor in my investigation. This will allow me to adjust the voltage to 1.
  • I will also use sellotape to make sure the wire stay straight along the wire so that the length is correct.
  • I also think that the range of lengths I used was not wide enough so I will measure the wire up to the length of 55cm and measure at 5cm intervals.

Prediction: I predict that the longer the wire the more resistance because as the length of the wire increases the number of collisions increase causing the resistance to increase. This will happen because by increasing the length of the wire, will increase the amount of electrons in the wire, these will collide with the atoms so therefore increasing the resistance.

Method:

  1. Get all the equipment needed :
  • 4 crocodile clips;
  • 4 normal wires;
  • An ammeter;
  • A  variable resistor;
  • A multimeter/ voltmeter;
  • Michrome wire – gauge 32, diameter 0.28mm;
  • Meter rule;
  • Power pack;
  • Sellotape.
  1. Set up the circuit:

image04.png

image05.png

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Conclusion

Improvements: if I were to do this experiment again the improvements I would make are:

  • That I consider the resistance in the rest of the circuit, because the length of the copper leads may have affected the total resistance of the circuit;
  • I could expand the experiment by using more lengths of the wire;
  • I could also use my gradient of my graph to calculate the amount of resistance per length of wire.

I could also expand the investigation by repeating the experiment but using different materials, so I could use a different material of wire and change the lengths – I think that the resistance will be different to other materials because they all have different atomic structures, so they will have different conductivities. But I would expect the resistance to increase steadily with the length of the wire increasing. I could also just use the same material but just increase the thickness of the wire and then change the lengths and see how thicker wires affects resistance. If I were to do this I would expect a low range of results for resistance for a larger diameter of wire. I will expect this because more current will flow through the wire and there will be less resistance, but this will only happen if I allow the same voltage to flow through the wires in both experiments.

Science Coursework                 

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