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Conducting Putty

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Introduction

 Conducting Putty

Aim: To investigate how length affects the resistance of conducting putty.

Background:

Resistance is worked out by using the equation ‘resistance=voltage/current’ and is measured in ohms. The higher the resistance, the lower the amount of current there will be flowing around the circuit. This means that if there if is a high amount of current flow, there will be a lower resistance.

Factors such as width of a wire, length of a wire, material of a wire and temperature affect the resistance in a circuit.  In a circuit, the electrons in the wires are a flow of tiny particles. These electrons are very small so can therefore pass between the atoms of the wires, each carrying a small electric charge. Electrons have a negative charge. The flow of this charge is called current, so the flow of the electrons is called current. Resistance is the amount of collisions between the electrons as they travel, because when electrons collide they slow down and oppose the flow of electrons.

In this experiment I will be using carbon putty instead of a wire. Carbon is not a metal, it is a semi-conductor and it does not behave like a wire when hot. Semi-conductors are poor conductors when cold but are better conductors when warm. Carbon is found in several forms and they have very different properties. The most common form is graphite, and one of the good things about graphite is that it conducts electricity.

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Middle

Keep the currant the same and connect the next length of putty to the circuit, and carry on doing this until all 5 lengths have been tested.Repeat the experiment 3 times, working out the resistance for each result using the formula ‘R=V/I’.

Before carrying out the experiment, preliminary work was done in order to find out which width would be best to use in order to achieve good, reliable results. I tested 3 different widths at 1cm, 1.5cm and 2cm.

Fair test:

To ensure that my experiment is a fair test I will keep the following factors the same:

  • The shape of the putty – I will achieve a constant shape by using callipers to make sure that the width of the putty is the same all the way across it. This is as the wider the width, the less the resistance there will be. I will put a 1p coin at each of the ends of the putty and clipping crocodile clips on to the pennies rather than onto the putty to ensure that it will not get squashed, or change the shape or area of the putty.
  • Temperature – I will keep the temperature the same by carrying out the experiment in the same room and by not opening any windows once the experiment has begun. The higher the temperature, the more the resistance.
  • Wires – I will use the same wires for each of my experiments to ensure they are all the same size. Also, the material of the wire should be the same each time as this may effect the outcome of the experiment.
  • Current – I will keep the current flowing through the wires the same to ensure that it will not affect the outcome of my results.
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Conclusion

 If I were to do the experiment again I would use a wider range of lengths and increase each length by 1cm each time. I would use the following method:

  1. Take some putty and using your hands roll it in to sausage like cylindrical shape. Use callipers to ensure that the putty is 1.5cm wide the whole way through.
  2. On a white tile and using a knife, cut the putty into different lengths using a ruler.(starting at 30cm and decreasing by 1cm each time until the putty is 1cm long).
  3. Set up the circuit as shown in the diagram above. Put 2p coins on the end of the putty so that the crocodile clips can be clipped on to them.
  4. Adjust the current to 6V and record the readings from the voltmeter on to a table of results.
  5. Keep the currant the same and connect the next length of putty to the circuit, and carry on doing this until all 5 lengths have been tested.
  6. Repeat the experiment 3 times, working out the resistance for each result using the formula ‘R=V/I’.

Other ways I could extend the experiment could be to use different materials such as putty, for example wire to see if I get a similar pattern of results and I could also change the thickness of the material.

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