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How does the Length of Pencil Lead affect Its Resistance

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              How does the Length of Pencil Lead

                         affect Its Resistance


Aim: The aim of this piece of course work is to find out how does the resistance of a pencil lead changes as I increase its length. And to find out what is the relationship between the length of a pencil lead and its resistance.  

Safety: Safety is a very important thing to consider as we doing a scientific experiment, so is this experiment. For make sure there will not be any accident as I doing this experiment, I will do the following things.

1, I will make sure I had set up the right electrical circuit before I let the electricity run through the circuit, to prevent the short circuit.

2, I will add a switch in the circuit, so that will prevent the lead get too hot to handle and to prevent the battery wasting.

3, I will be careful when I am holding the pencil lead because it would burning your skin if it got to hot.

Fair Test: I will try to make this experiment as fair as I can, therefore I would be able to get some reliable results.

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Prediction: I predict that the length of pencil lead will be directly proportional to its resistance, which means the longer the lead have the bigger resistance. This should produce a straight-line graph where resistance doubles when length doubles (see following page). I predict this because the resistance in a conductor is due to collisions between electrons and the particles of the conductor, therefore a piece of lead twice as long as another will have twice the number of particles and the probability for collisions will consequently be double, meaning double the resistance.

This is what I predict the shape of the graph will look like:    

Analysing and Concluding:

  The graph 1 shows the length of pencil lead against its resistance. My results did not reflect my prediction perfectly well, it shows that they have the directly proportional to each other but it did not show the double length have double resistance. The line has crossed y-axis at 3.9263 that is not right because it should be crossed it at 0. I have found out the equation of my line which is y=1.0295x+3.9263 by mathematical method, I should get the equation y=x but I actually got the plus-3.9263.

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  To improve my method to get more reliable results, I will do the following things. Firstly, I will choose something else to instead of crocodile clips, which have more contacting area with the lead; therefore it will allow the electricity passed more easily. Secondly, I will carry out this experiment more time and I will finish all the experiments at the same time, which means I will not do the whole experiment separately.

  To extend this experiment, I will do the following steps. Firstly, I would choose the other compositions of the pencil lead to investigate, such as 2B, 4B or 6B. Secondly, I would try to find out how does the thickness of the pencil lead affect its resistance. Thirdly, I could investigate the relationship between the temperature of the pencil lead and its resistance.        

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