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# An investigation into the theory of resistance

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Introduction

An investigation into the theory of resistance Resistance of a wire An electric current is the flow of electrons through a material. The Current through a wire is proportional to the potential difference across it. Plotting a graph of P.D against current would give a straight line graph through the origin. P.D (V) [image002.jpg] I (A) The gradient of the line (V/ I) is a constant and is called resistance. Resistance is measured in ohms (Ohm). The graph above is an ideal case where there is no temperature change of the wire during the time that measurements are being taken. This will not be the case as passing an electric current through a wire causes it to heat up, as in an electric kettle or electric fire. By setting the following circuit it is possible to determine the resistance of a wire: [image004.jpg] ( [image006.jpg] = wire sample) Planning I shall apply an electrical current through a piece of wire one hundred centimeters long. I will be taking readings of current and P.d. every 10 centimeters. With the information I gather, I will then be able to calculate the resistance using the formula: Voltage (V) = resistance (Ohm) Current (I) Aim I aim to carry out an experiment which will enable me to show a relationship between length of a wire and resistance of a wire. ...read more.

Middle

P.d. (V) Current (A) Resistance (Ohm) 0.0 0.03 0.65 0.05 10.0 0.40 0.46 0.87 20.0 0.60 0.30 2.00 30.0 0.67 0.30 2.23 40.0 0.75 0.28 2.68 50.0 0.80 0.23 3.48 60.0 0.96 0.19 5.05 70.0 0.95 0.19 5.00 80.0 0.95 0.18 5.27 90.0 1.17 0.12 9.74 100.0 1.03 0.16 6.44 From this table I have realised that my prediction was actually correct, the further the length the higher the resistance. My table reinforces that prediction except for two readings (IN BOLD), these are the anomalies. These readings at 70cm, which is too low, and at 90cm, which appears to be far too high, could be due to many reasons. These reasons could be endless, one for example could simply be a poor connection. From completing my pre-test trial I have decided I will make no alterations whatsoever, I believe my preliminary investigation was quite successful and straight forward. Moving on from this somewhat simply completed pre-test I will carry out my actual results within the main experiment, in this main bulk of my investigation I shall redo the experiment and record my results as shown above 3 times, calculate the average, draw up a series graphs and evaluate (as explained in the method). Results Table The following table is my recorded three experiments and the calculated average's and the average resistance: Length of wire (cm) Test 1 Test 2 Test 3 Average Resistance (Ohm) P.d. (V) I (A) P.d. (V) I (A) P.d. (V) ...read more.

Conclusion

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