An investigation intoThe resistance of a wire

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An investigation into

The resistance of a wire

Physics Coursework

Ben Smith, 10S

Aim: To discover if a relationship exists between the length and resistance of a wire.

Prediction: I believe that I will discover that the resistance of a wire increases proportionally with the length. I think that this is due to the way resistance occurs in a typical wire.

Resistance is the result of negatively charged electrons (the actual current) colliding with the positively charged ions that make up the wire. The collisions cause the energy in the electron to be lost, and when they occur on a larger scale there is a noticeable difference between the start and end voltage of a circuit.

As the length of the wire increases, so must the number of particles. As the number of particles increases, so will the number of collisions, and therefore the amount of resistance encountered.

George Ohm discovered that the voltage of a circuit is directly proportional to the current flowing through the circuit, meaning that if you triple one, you triple the other. He then came up with a rule for working out the resistance of a circuit (rearranged from his original equation):

Resistance = Current / Voltage

This is the formula I will use to calculate the resistance of the wire.

A wire, showing collisions occurring

If you double the length of the wire, I believe you will double the resistance.

Background:

The flow of charge in a wire is called the current. It is expressed in terms of the number of "coulombs" per second going past a given point on a wire. One coulomb/sec equals 1 ampere (symbol A), a unit of electric current named after a French physicist.

I have explained how resistance occurs above, and volts are an expression of the amount of energy being carried by the electrons flowing through a circuit. The electrons are negatively charged, and move round the circuit (from the negative side to the positive side of the battery) as a result of attraction to the protons.

Plan:

I will carry out the experiment by first affixing the 100cm length of the chosen wire to a ruler, using sellotape.
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I will then set the power supply to approximately the right voltage, and then use the variable resistor to set the exact current (measured on the voltmeter). I have to use this method because the PSU itself is not accurate enough for our purposes.

Once this preparation is complete, I will attach the first crocodile clip to one end of the ruler, and the second clip at the first distance, completing the circuit drawn below. The power supply will then be turned on long enough for the measurement to be taken, to prevent the wire heating up.
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