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# Resistance of a wire.

Extracts from this document...

Introduction

Philip Jacobs 11R

Resistance of A Wire

Theory and Background Write Up

Wires have resistance because they have thousands of atoms inside them. When voltage flows through a wire the electrons hit these thousands of atoms. This slows down the electrons. This slowing down process is what we call resistance. The electrons always travel from negative to positive on diagrams, although in conventional current it actually flows in the other direction.

## Figure 1 – Inside of a Wire

_+

### The resistance of a wire can be altered depending on the following: -

• The material of a wire – This can be because some wires have more atoms inside them than others do.
• The temperature of the wire – If there is a high temperature in the wire then the atoms will vibrate more. This means that electrons are more likely to “hit” the atoms.
• The cross-sectional area of the wire – When the cross-sectional area of a wire increases the resistance of a wire goes down. This is because the area that is occupied by atoms is reduced.
• The length of a wire – When the length of a wire is increased so is the resistance of that wire. This is because there are more atoms inside a longer wire.

The factor that I have chosen to investigate is how the length of a wire effects the resistance of the wire.

Middle

The procedure that I use in my main experiment will be slightly different to that of my preliminary experiment, this will be because I will collect 10 sets of results and will then repeat the experiment for a total of 3 times.

I predict that in my main experiment I will find that the resistance of a wire is directly proportional to the length of a wire. I have predicted this due to the results I gathered in my preliminary experiment and from my background work which was that when the length of a wire increases so does the resistance.

Main Experiment

Diagram

Apparatus

In my main investigation I used 1 meter of constanton wire, 2 crocodile clips, 6 coated wires, 1 power pack, 1 ammeter, 1 jockey key, 1 voltmeter, 1 meter ruler, 8 pieces of cellotape (3cm each) and 1 pair of scissors.

Method

1. I plugged a power pack to a plug socket and connected a wire to it. I put this wire in to my ammeter.
2. Out of this ammeter came another wire on the end of this wire was a crocodile clip which I attached to the constanton wire which had been attached to the meter ruler.
3. Connected to this crocodile clip was another crocodile clip which via another wire led to a voltmeter which was in parallel to the meter ruler.
4. Coming out of the other side of the voltmeter was another wire.

Conclusion

When I did my main experiment there were only two changes in apparatus and procedure. The change in apparatus was to use a jockey key to connect to my piece of Constanton wire with the rest of the circuit to give me my readings. Before using a jockey key I used a crocodile clip, this didn’t give me a reading as accurate as the jockey key. This is because it is very hard to keep the crocodile clip steady to give an accurate reading without the ammeter and voltmeter flickering. The only change to my procedure was to collect ten pieces of data instead of seven in my preliminary investigation. Also once I had collected the results I repeated the experiment a further two times. Perhaps if I were to do the experiment again I would measure fifteen different lengths and repeat it four times. This would give me an even better set of results and would then give me an even more accurate results graph.

To learn more about the resistance of wire I could have done more experiments. The experiments that I could have done are: -

• To have changed the material of the wire
• To change the temperature of the wire using a optical pyrometer. An optical pyrometer allows you to measure the temperature of a wire without touching it.
• To have changed the cross-sectional area of the wire using a micrometer. A micrometer used with a microscope accurately measures small distances, like that of a wire.

This student written piece of work is one of many that can be found in our GCSE Electricity and Magnetism section.

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