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A manufacturer of resistors uses a variety of wires to make resistors of fixed values. You are to carry out tests to investigate how he can produce resistors with different values of resistance.

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Introduction

Problem and Planning Experimental Procedures Problem: A manufacturer of resistors uses a variety of wires to make resistors of fixed values. You are to carry out tests to investigate how he can produce resistors with different values of resistance. Background Knowledge: What is resistance and what causes it? The more resistance a component has, the more voltage is needed to make a particular value of current flow through it. The unit of resistance is the ohm and is represented by the Greek letter ? (omega). Definition: A wire has a resistance of one ohm if a p.d (potential difference) of one volt is needed across it to make a current of one ampere flow through it. Ohms Law The equation that comes form Ohms law is very useful for calculating values in electric circuits. Factors affecting Resistance Firstly, the length and the cross section of wire can affect the resistance. We use an ammeter to help us find the resistance. Secondly, if we take two wires of different materials, both 1metre long and 1mm2 in area and we measure their resistances, we find that one has a much higher resistance than the other. ...read more.

Middle

We put into the circuit two crocodile clips. When nothing is attached here, the circuit is incomplete but when we connect the different lengths of wire, the circuit is complete. For each length of wire, we will make 3 attempts; the first will be against a current of 0.2 amps, the second, 0.6 amps and the third - 1.0 amp. To adjust the current each time, we turn the dial on the power unit and to attain the precise current, use the rheostat slider while observing the ammeter. We will then record the readings of the voltage each time. The reason we repeat the experiment three times, is to make sure that are recordings are accurate and to give us more results to record to reinforce our predictions. After observing the experiment we tabulate the results to make them easier to examine. From these results, we will then construct a graph showing length against resistance. We will examine the graph and look fro any correlations or patterns that we could link to our conclusions. Safety: When increasing the current from the power supply, we must be careful not to increase it too far otherwise the wire may get very hot and snap (This is due to the melting point of the wire being exceeded) ...read more.

Conclusion

From the results we can see that when we increase the current against the different lengths, the voltage increases each time. When we calculated the resistance (i.e. R=V/I) we could clearly see that the margin in the resistance fro each length of wire against the different voltages was within 0.8/0.9 of an ohm out each time and so they were very alike. 20 0.55 0.57 0.55 40 1.05 0.98 1.00 60 1.55 1.53 1.43 80 2.10 2.05 2.11 From these results, we can draw the conclusion that: The longer the wire, the more resistance it has. Shown above in the results. As we have drawn this conclusion from the results, I am confident that my results support my prediction. I feel that the design of the experiment was reliable and the results that were produced from it are accurate. The only improvements I see that could be made to the experiment are 1. The measuring of the lengths of wire 2. The adjusting of the rheostat to attain the current. Fortunately, the experiment produced good results meaning we had no anomalous results. I feel that it is for this reason, my results are strong enough to support my conclusion as already stated above. ?? ?? ?? ?? GCSE Coursework ...read more.

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