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What effects the electrical resistance of a wire?

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Introduction

GCSE PHYSICS COURSEWORK                                                                  Moe Shimizu 11G

PLANNING :

The problem : What effects the electrical resistance of a wire ?

Background knoweledge :

Resistance is measured by the following equation:

R = V / I

Ohm's law states that the amount of current flowing in a circuit is directly proportional to the voltage of the circuit and inversely proportional to the total resistance of the circuit.  For my experiment, Ohm’s Law shows that if the current increases or decreases, then the voltage will increase or decrease accordingly and propotionally.    Knowledge that I already have of Ohms law is how to measure resistance using a voltmeter and an ammeter. The law is usually expressed by the formula I = E/R, where I is the current in amperes, E is the electromotive force in volts (voltage), and R is the resistance in ohms. (This enables us to work out the resistance using the current and voltage:
R=V/I.)  I will measure resistance by using an ammeter for current and a voltmeter for voltage.

Energy from a cell is carried along through a circuit, because charged particles move within leads or connecting wires giving energy to another particle.  These charged particles are known as free electrons.  This is called electrical conduction. Connecting wires and leads are excellent conductors of electricity and do not affect the flow of these electrons.

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Middle


the atoms are moving into the path of the electrons. This increase in collisions means that there will be an increase in resistance. Therefore resistance is greater.  As I have to ensure the temperature is constant (Ohm’s Law), I will make certain that I do not leave the energy supply on for long periods of time.  For extra accuracy, I will use the thickest wire to avoid over-heating, which is 28s.w.g.

Thickness also varies the resistance.  In a thick wire, there is less resistance because there is more surface area for the free electrons to move and avoid collisions with atoms.  Narrow and thin wires restrict the surface area in which electrons can move, therefore the resistance increases.  I will keep the thickness of my wire as 28s.w.g to avoid dramatic change in resistance.

The type of wire also varies the resistance. Different metals have different atomic structures, and this means that they have different resistances.  The more atoms metals have, the higher the resistance.  To prevent affecting the constant resistance throughout each of my experiments, I will only use one material.

The equipment I use must also not change throughout the experiment, as different batteries may have different voltages.

Results:

I am planning to take 3 sets of 8 results for a reasonable and suitable average.

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Conclusion

- I found that although I used 28s.w.g constantan which is on the outside of the wire board, the crocodile clips managed to touch the other wires.  I must set up my experiment so that the wires do not touch.

- For future reference, I discovered that the wires on the board are not straight and there are kinks that I cannot fix.  This may restrict my experiment.

I also drew a graph to show whether my experiment is dependable, and whether there are any anomalous results.  This also showed whether my experiment needed development or not.  In my graph, I plotted the length of the wire against the average resistance of the wire.

This graph shows a positive correlation, showing that my experiment will be suitable.  In spite of this, there is a single anomalous result.  I believe this is because of many possible reasons. For example, the equipment (crocodile clips in particular) may have been flawed or damaged.  The temperature may also have affected the experiment, by over-heating slightly.  Also, I may have made a error while taking my readings.  For these reasons, I will ensure that I use suitable equipment and record accurate results.  

The graph also supports my prediction.  In spite of the anomalous result, my graph showed a positive correlation, so I feel my experiment will go well. I also feel that changing my material to another wire that my school provides, nichrome.  Hopefully, this will help me to prove my prediction once again.

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