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# How can I change the resistance of a wire?

Extracts from this document...

Introduction

Physics Coursework

How can I change the resistance of a wire?

Introduction:

Electricity is conducted through a wire, it moves using free electrons – the amount of free electrons depends on the type of wire, the more free electrons the more conductive the wire.  Free electrons are what are called ‘given energy’ so they move and collide with other free electrons beside them.  These collisions or ‘jumps’ as they are sometimes called; occur all the way down the wire, and this is how electricity is conducted.  Each time they collide it converts some of the energy the free electrons have in to heat. And that is what RESISTANCE IS THE RESULT OF KENITIC ENERGY LOST AS HEAT.

Ohms law is also quite important to this; in 1826, George Ohm discovered that: the current flowing through a metal wire is proportional to the potential difference across it (providing the temperature remains constant).  It says that the current is proportional to the voltage.  So if you double the voltage the current doubles to.  This also comes into play with the length of the wire, if you double the length of wire, the resistance doubles too.

Middle

Diagram:

Preliminary work:

I did a preliminary test so I could see if the experiment produced useful results.  I tested two lengths of wire and if there is a noticeable difference between the 2 then the experiment will be a success.

 Length Current(Amps) Voltage(Volts) Resistance (Ohms) Short 0.88 3.00 3.41 Long 0.50 3.00 6.00

I have decided not to change the method of carrying out this experiment because the results suggest that there is a noticeable difference.

Results:

Conclusion

Evaluation:

I have a lot of confidence in my results; I think that I have collected them quite accurately.  There doesn’t appear to be any results that are very out of place, they are all close to the line of best fit.  I think the experiment procedure made the best use of the equipment available to me.  My prediction was also pretty accurate, so I have a lot of confidence in that also.

To make the results more accurate I could have used digital voltmeters and ammeters because I could have easily made errors when reading off the measurement, a digital one would give an exact number with decimal places that I would not be able to read off the normal meter.  If I had used something more like a knife blade, instead of crocodile clips – which are quite wide, to clip the wire then the measurement of wire would have been much more accurate.  The wire may have been tarnished, so to make sure it wasn’t I could of used some glass paper and smoved off the wire.

I could have used a totally different variable, which would change my results completely.

Overall I feel that my results were as accurate as I could have made them with the equipment I had available to me.

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