Factors affecting the resistance of a wire.

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Hannah Marchant

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Factors affecting the resistance of a wire

Introduction:

Resistance is a force, which opposes the flow of an electric current around a circuit so that energy is required to push the charged particles around the circuit. The circuit itself can resist the flow of particles if the wires are either very thin or very long. E.g., The filament across an electric bulb is quite thin as it needs to resist the flow of particles for the bulb to glow.

Resistance is measured in ohms. George Ohm discovered that the electromotive force of a circuit is directly proportional to the current flowing through the circuit. This means that if you triple one, you triple the other. He also discovered that a circuit sometimes resists the flow of electricity. He called this resistance. He then came up with a rule for working out the resistance of a circuit :

V/I = R

V - Volts

I - Current

R - Resistance.

Plan: Three external factors influence the resistance in a conductor. Thickness (cross sectional area of the wire), length, and temperature all have some effect on the amount of resistance created in a conductor. The fourth factor is the conductivity of the material we are using. Some metals are just more electrically conductive than others are. This however, is considered an internal factor rather than an external one.

For the temperature of the wire, I would not be able to carry out a fair test because it is extremely difficult to produce and control the range of temperatures needed without the correct equipment. If I chose to measure the difference in the resistance in different widths I would find it difficult to obtain different widths with out having to increase the width by doubling the wire like so.

The final factor is the length of the wire. To measure and record the findings for this factor would be simple and the results collected could show a connection between the length of the wire and the resistance given by the wire. This is why I have chosen to investigate this factor.

Prediction: I think that as the length of the wire increases so to will the resistance of it. I also believe that the rate at which the resistance of the wire increases will be directly proportional to the length. The graph to show this should therefore look something like this:

Reason: The best way to describe what will happen is through an analogy. Imagine the charge that is flowing through a wire to be water flowing through a pipe. The Rate at which the water is flowing is the current in an electrical system. Resistance is what restricts the movement of the charge through the wire. The length of a pipe, the cross-section, and the imperfections in the pipe (clogs and such) all impede the flow of the water, and are analogous to how electric current is impaired as it flows through a wire. Things like making the wire longer and thinner make the resistance go up since it is harder to push a charge through the wire. Therefore, you can see that resistance is inherent in every type of wire. There are cases when some materials can be cooled down to temperatures where they have effectively zero resistance, but in everyday electrical encounters this doesn't really have much bearing these are called superconductors.

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With electricity, the property that transforms electrical energy into heat energy, in opposing electrical current, is resistance. A property of the atoms of all conductors is that they have free electrons in the outer shell of their structure. (All metals are conductors and have an arrangement in similar form to diagram A)

As a result of the structure of all conductive atoms, the outer electrons are able to move about freely even in a solid. When there is a potential difference across a conductive material, all of the free electrons arrange themselves in lines moving in the same direction. ...

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