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Resistance of a Wire Investigation

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Introduction

I am going to investigate factors that affect the resistance of a wire. Resistance is measured in ohms. The symbol for an ohm is ?. A resistor has the resistance of one ohm if a voltage of one volt is required to "push" a current of one amp through it. A flow of electricity is a flow of electrons. Imagine a row of electrons, sitting in a wire (for simplicities sake, I will not draw the nuclei). Because we know electrons repel each other, they will spread out as much as possible. Now, suppose an electron is inserted in the left hand end. This would occur if a higher electron pressure were to be at one end than the other, forcing an electron onto the wire. The electrons on the right side force out an electron to the negative positive of the battery. This allows the electrons to spread out and the wire is as before, only the electrons are all one further to the right, and an electron has left the wire. Now, I stated earlier that electricity was a flow of electrons. This means it can be likened to a flow of anything else. As an analogy, I will compare it to a flow of water. The water wheel and the bulb both provide resistance. That is to say they both transform the energy pushing the flow into another sort of energy. Another sort of resistance can be likened to water flowing through a thin pipe. ...read more.

Middle

I will not investigate the effects of changing the temperature of the wire as the effects of temperature are small so consequently a large range of values is required, which is difficult to attain in classroom conditions with any degree of accuracy. I will not investigate the effects of the diameter of the wire as few values of this are available to me in school and it involves using different reels of wire which may for example have decayed or tarnished, so a fair test is not absolutely guaranteed. Therefore I am going to investigate the length of the wire as it is easy to vary, uses the same piece of wire and allows easy re-tests, as well as being quantitative so allowing a conclusion to be formed. I did some preliminary testing that showed copper gave such a small resistance that it was difficult to get any accurate results and generate a conclusion. I will use Constantan because it does. Also, room temperature is the easiest to guarantee so I will use that. I found 10 cm a suitable minimum length as any less meant just a small change in length, as little as 1 mm, made, for example, by misaligning the crocodile clips or having kinks in the wire, could lead to large differences in results. Prediction I predict that the resistance of a wire is directly proportional to its length. This is because when current is flowing in a piece of wire, electrons are moving through the ions that constitute the wire. ...read more.

Conclusion

The line shows that seemingly, a zero-length of resistive wire gives a small resistance. This is explained by the equipment; the wires and components used, such as the ammeter and voltmeter, had themselves a small, though by no means negligible, resistance. Although it does not affect the gradient of the graph, it must be noted that the resistance of the wire is actually a small amount less than plotted. Sources of error The experiment was not perfect; for example, the measuring equipment that was used was only accurate to 0.2 units. The equipment itself may also have been slightly un-calibrated or inaccurate. Measurements were taken by eye; this means the angle of the eye may have affected the reading, and human decision affected which value was taken. In addition, the temperature of the wire varied slightly at low lengths and high voltages; they became hot to the touch and at higher voltages actively burned up; this is why lower lengths have fewer readings. This means the averages are less reliable, and the resistance may have been altered by the heat giving nuclei more energy, making them move more, collide with electrons more and thus slow the electrons. The heat originates from the resistance of the wire; electrical energy cannot simply disappear, and this wire converts the electricity to heat energy as it resists. This is more significant in shorter pieces of wire because there is more current passing through each unit of wire, thus there is more energy that can be converted into heat. ?? ?? ?? ?? Martin Smith 1/2 Centre no. 26146 Physics Coursework ...read more.

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