An investigation into factors affecting the resistance Of a metal wire.

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      An investigation into factors affecting the resistance

                             Of a metal wire

What is resistance?

 

Electricity is conducted through a conductor, in this case wire, and travels through free electrons. The number of free electrons depends on the material being used and the size of it. The more free electrons the better the conductor, i.e. it has less resistance. For example, gold has more free electrons than iron and, as a result, it is a better conductor. The free electrons are given energy and as a result move and collide with neighbouring free electrons. This happens across the length of the wire and thus electricity is conducted. Resistance is the result of energy loss as heat. It involves collisions between the fixed particles of the metal, free electrons and impurities. These collisions convert some of the energy that the free electrons are carrying into heat.

 

How is it measured?

We measure resistance in units called ohms (Ω).The resistance of a length of wire is calculated by measuring the current in the circuit and the voltage across the wire using mille ammeters and volt meters. The current must flow through the volt metre and mille ammeter. These measurements are then used in this formula:

 V = I / R                     where V = Voltage, I = Current and R = Resistance.

This can be arranged to   R = V / I

Length, area, temperature and material might affect the resistance in the wire in many ways. If you were to measure two different length wires, one with a length of 100cm and the other with a length of 50cm, there would be more resistance in the longest wire. So we know that this is a big factor that affects the resistance. Area is a little trickier to be precise but still affects the resistance as the bigger the wire the less resistance. This is because there are more free electrons to pass through with. The temperature affects the resistance less than length and area. The wire may heat up as it resists the current flowing through it. As the temperature increases so does the resistance. The material the wire is made of is also a factor affecting the resistance. Although the change is very small it still makes an affect on the resistance.

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The factor I have chosen to investigate

I have decided to investigate how resistance is affected depending on the length of wire.

Control of variables

In order to keep this a fair test I will have to keep the variables constant throughout the experiment. This means that the wire will have to remain the same temperature, have the same cross section and be made of the same material each time. I will use the same equipment throughout the experiment as some of the wires will have different resistance. The power level will remain ...

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