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Find out how the thickness of a wire affects the resistance.

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Introduction

Title Electrical Resistance

The aim of this investigation is to find out how the thickness of a wire affects the resistance.

Background Knowledge

Structure of a metal:

A metal consists of a huge structure of atoms, which have released their electrons from their outer shell to form a ‘sea’ of electrons. Releasing the electrons causes the atoms to become positively charged ions. This leaves the metal atoms surrounded by a ‘cloud of electrons’. A metal item is like one big atom with many nucleii but only one electron cloud. Instead of the atoms having their own electrons, the outer electrons of each metal atom leave the individual atoms and create a sea of free electrons throughout the metal. This allows the outer electrons of each atom to move freely as they orbit among all the atoms as a whole. The sea of electrons is there merely to hold the ions together, however if a potential difference is applied to the metal, these electrons are free to move.

When these free electrons move around, an electric current is produced. In other words, an electric current in a metal is made up of electrons

supplied by metal atoms. A current is not ‘injected’ into the metal from outside. Instead electric fields caused by the power supply cause the wandering electrons to begin flowing. The power supply is not the source of the electrons.

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Middle

Each time I do the experiment, I will cut the desired piece of wire of a certain SWG (Standard Width Gauge), using pliers, to 1.lm. In my experiments, the length of wire that the current will flow through is going to be im long. The reason that I will be cutting the wires to 1.lm is so I have an extra 10cm so I can place the crocodile clips Scm in from each side of the wire. I will coil up the wire in between the crocodile clips. This means the length of wire that the current will flow through is im seeing as the electrons will only flow between the crocodile clips.

The length of the wire affects the resistance. If the length of the wire is increased then the resistance will also increase, as the distance the electrons will have to travel will be longer. In other words there are more atoms in a longer wire for the electrons to pass through. This means more collisions will occur.

Collisions are when particles collide with one another. In this case, a longer wire means more atoms, and more atoms means more chance of the electrons colliding into them. Collisions slow down the rate at which the electrons are travelling in, and therefore cause a higher resistance. Due to this fact, the length increase should be proportional to the resistance increase.

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Conclusion

This is because of the increase in the space for the electrons to travel through. bue to this increased space between the atoms there should be less collisions. Less collisions means less resistance. This means that the thicker the wire, the more space for the electrons to travel through, meaning less collision.

ADparatus

® Micrometer-screw-gauge

® Variable resistor

® Ammeter

® Voltmeter

Tray

® Beaker

® Pen

® Connecting wires

® Scissors

® Pliers

® Meter ruler

® Power pack

® Thermomet

® Goggles

® Crocodile clips

® Calculator

How to measure

I will use the micrometer accurately, n use the meter stick in the correct way, to make sure all my measurements are accurate. My results will be verified due to me doing the test on each thickness of wire 10 times, with different current each time. I can be sure whether my results are precise by working out the resistance from the currents and the voltage.

Analysis

I did a graph of my results of the cross sectional area of the wire against the resistance. This gave me a reciprical graph, which did not give me a clear conclusion. I needed to redraw the graph with 1 over the cross sectional area. This gave me a straight line graph, and from that I could make out a very apparent result,

Evaluation

From the graphs, I can see that my prediction was correct. As you increase the thickness of the wire, the resistance decreases.

...read more.

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