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

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Introduction

 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

...read more.

Middle

Prediction

The longer the wire, the higher the resistance. This is because the longer the wire, the more times the free electrons will collide with other free electrons, the particles making up the metal, and any impurities in the metal. Therefore, more energy is going to be lost in these collisions (as heat).

Preliminary experiments

Before the real experiment I carried out some preliminary tests to check a few things. I checked how much power would be needed to keep the ammeter below 2 amps. I then did some tests involving the wire I would be testing. I found that if I use thick wire with a high voltage, the wire gets very hot and this would affect the resistance. So I then decided to use a thinner wire with a low voltage. The current was so low I decided to use a mille ammeter as it is more accurate. I had to make sure the current didn’t go above 200 mA at all lengths. If it did it would mean the current is too high.

  I fastened the wire to the meter ruler at three different points. I noticed that when I attached the crocodile clips the wire began to coil up. This would mean that the length I would be testing is inaccurate.

Proposed method

(Diagram on the page after this)

...read more.

Conclusion

The line of best fit clearly shows that the results followed the expected pattern very well. The points are very close if not touching the line. This shows how the results were directly proportional through out, as the gradient remained the same.

Evaluation

My experiment may have been slightly inaccurate, as there are a few minor details that I did not check. These include that the wire may not have been the exact length as it is very hard to get it exactly the right length just by looking at it. I could have used a more accurate measure and got it exact every time. Also the metre stick was old and may not have been accurate. Over night 2 of my wires had been taken so I had to replace them and start over. If I hadn’t the wires could have different resistances. All these potential problems could have very slightly affected the results but as it was so insignificant it didn’t matter too much.  The resistance of the crocodile clips and wires linking everything together would affect the results as their resistance would have added to the resistance of the nichrome wire.  think my experiment went very well as I did not have to repeat any lengths. At first I didn’t know how to set up the circuit but after I figured it out it was fairly easy.

...read more.

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