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# What Factors Affect the Resistance of an Electrical Conductor?

Extracts from this document...

Introduction

## Leanne Heath 10 Derby 1

What Factors Affect the Resistance of an Electrical Conductor.

The key factor I am going to investigate is what affect different lengths of wire has on the resistance of the wire.

## Hypothesis

Resistance is the force which opposes the flow of electrons through an electrical conductor. Resistance occurs when the negatively charged electrons travelling along the current in the wire collide with the positively charged atoms of the wire. Hence the atoms are the property which opposes the flow of electrons. These collisions slow down the flow electrons, causing resistance. The electrons have to try to avoid, or travel around the atoms, therefore the flow of current is slowed down. The amount, size and density of atoms have an effect on resistance. The circuit itself holds some resistance.

There are 3 factors which can affect resistance. These are :

• The material of the wire
• The length of the wire
• The diameter of the wire

The material of the wire is a very important factor. Different wires contain different numbers of atoms. Some wires have lots of atoms, whereas others have few atoms. A wire that does not easily conduct electricity would be said to be a bad conductor of electricity. An example of a metal conductor that does not easily conduct electricity is called nichrome. Wires that have many atoms will have a high resistance compared to wires which have a few atoms which have a low resistance. Wires have a high resistance because there is a smaller area for the electrons to pass through, because there are a large number of atoms present in the wire. Large numbers of atoms reduce the amount of area for the electrons to pass through. Also the size of these atoms can change. Some atoms are large compared to others which are small.

Middle

In the investigation I will also take 2 readings and then an average. This will reduce any anomalous results occurring.

Apparatus

The apparatus that will be used in this investigation is:

• Digital Voltmeter 0-20V – measures voltage across the wire.
• Digital Ammeter 0-10A  – measures current flowing through the wire.
• Power Pack
• Boiling Tube
• Variable resistor 0-25 Ω.
• Crushed ice
• Circuit board
• Constantia wire
• Crocodile clips
• Connecting wire
• Circuit board
• Insulation tape
• Rubber bung
• Switch

Fair Testing

To make sure that this investigation is a fair test:

• Use the same material each time (Constantia wire)
• Keep the diameter of the wire the same
• The temperature must be kept constant.
• Must use new wire each time. Old wire may still hold an electrical charge which would affect the resistance.
• Don’t let the wire touch as this causes the wire to short out decreasing the length of the wire.
• Switch the power supply on for the same amount of time.
• Stop taking readings after all of the ice has melted.

Ice will be used to keep the temperature constant. Ice is used because its temperature stays constant until all of the ice has become a liquid. Therefore when of the ice has melted and become a liquid the temperature rises. That's why the investigation has to be stopped when all of the ice has melted.

To stop the wire touching I will place insulation tape around the wire as it is being wrapped around the test tube. This will stop the wire from moving around which means that the wire will not touch and short out.

Safety

To make sure that this investigation is safe the following aspects should be taken into account:

• Don’t touch the wire and the boiling tube just after the investigation has been done because the wire will still be hot.
• Don’t use faulty wires or a faulty power pack.

Method

Conclusion

The 60cm wire could have already been used. This means that it could have still held an electrical charge which would increase the resistance of the wire. Also all of the ice in the boiling tube could have melted meaning that the temperature would have increased, resulting in the resistance being increased.

If I could repeat the investigation again there would be a number of changes that I would make. One of these changes would to decrease the lengths of the wire. The 100cm wire was too long and it was difficult to wrap the wire around the boiling tube without any of the coils touching. Also I could have used a bigger boiling tube that had a wider diameter. It would be easier to wrap the wire around the boiling tube without any of the coils touching.

Also if more repetitions were done there would be less chance of anomalous results appearing.

If I did the experiment again I would change the ice after each experiment. Therefore none of the ice would melt completely and the temperature wouldn’t rise

I don’t think that the voltmeter and ammeter were read incorrectly because there are no massive changes in the two reading on the table.

If I was to repeat the investigation I would make sure that the wire was new wire that hadn’t been previously used and that the wire came from the same strip.

I wouldn’t change my graph because I fell that it is clear and easy to see where each length of wire is.

## Below is a list of web sites that I used to fin out background knowledge for the investigation:

www.essaybank.co.uk

www.goggle.com

www.sciencefinder.org

www.sciencenet.org

Here is a list of books that I used in my investigation:

• Coordinated Science – Physics

Also I use Encarta 99 to find out information for the investigation.

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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