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What affects the resistance of a wire?

Extracts from this document...

Introduction

Physics coursework*

In this experiment I will be describing the potential difference (or voltage) as the electrical ‘pressure’ pushing the charges around the circuit. I know though that some of this pressure is dropped while pushing the charges through any form of electrical resistance in the circuit. So, the potential difference across the two ends of a resistance is just the pressure dropped across the resistance.

WHAT IS RESISTANCE?

Current is a flow of tiny, negatively charged electrons through a conductor

Like a metal wire, Metals are particularly good at carrying a current, because they have lots of “free” electrons. This means electrons which are not bound onto a particular atom in the wire, will move through the wire if you drop the pressure across its ends. The number of free electrons depends on the material, the more electrons flowing freely the better the 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.

The property of the conductor restricts the flow of electricity through it.

Resistance is the result of electrons; motion is impeded. It involves collisions between the free and the fixed atoms of the wire material, and other free electrons and impurities causing less current to flow.  These collisions convert some of the electrical energy that the free electrons are carrying into heat.

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Resistance opposes current, which is the flow of negatively charged electrons.

...read more.

Middle

        Power pack

image01.png        Ammeter

image01.png        Voltmeter

image01.png        Copper wire

image01.png        Meter Ruler

image01.png        Crocodile clips

image01.png        Connecting Wires

image01.png        Digital multimeters will be used to measure the voltage and current this is because it is more precise and therefore easier to read. If I were to use an analogue, which has a tiny like needle that keeps on moving slightly, it would be much harder to read off.

The circuit will be set out exactly like this.

 METHOD

 To ensure that this investigation will go well I will stick to the method below:

image01.pngThe equipment is set up as shown in the diagram.

image01.png         A metre long of wire is attached to a metre rule. The positive crocodile clip is attached at 0cm. And the negative (which is used as the sliding contact) is firstly set at 100cms.

image01.png        The power pack is then switched on; the voltage is increased until 0.3Amps shows on the ammeter.

image01.png         The voltage and current is then taken, which is read off the voltmeter and the ammeter, and then recorded.

image01.png         The power pack is switched off (to make this investigations safer for the next use and also so that we do not mix the previous readings with the current use.)

...read more.

Conclusion

These results could be done better. If I were to do this experiment again, I would use a longer duration for the investigation. Because we only had a fixed duration for this investigation it is more likely to create complications then get rid of them. I would use newer, more accurate ammeters and voltmeters,the experiment will be done three times with different ammeters in case of any damaged or old equipment to gain more accurate results, a more accurate method of measurement, and take a much wider range of readings, and more readings so that a more accurate average can be taken. I would also investigate other factors, such as temperature, voltage and current, and see how these affect the resistance. I would also do the experiments under different conditions such as temperature and pressure to see if it makes any difference to resistance.

 To further investigate, I could increase and decrease the cross-sectional area of the wire just by adding more wires and seeing if this too will affect the resistance. I already know though that the larger the cross-sectional area is the lower the resistance, this is because the negatively charged electrons moving in a current are spread out over a greater area. There is less chance of a negatively charged electron to collide with an atom, so more current can flow. Increasing the thickness of a wire decreases its resistance. I would still investigate this to make sure I am certain of my judgement.

...read more.

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