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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

- Temperature (collision speed alterations) To improve the accuracy of my experiment It would have been helpful if: - The wire was in a temperature controlled environment, this is because resistance is affected by temperature. - The voltmeter and ammeter were difficult to take a reading off, this is due to the unsettling of the actual readings, they flicker and change several times before stopping on a final reading. If you move slightly however, the results will flicker again and become distorted. To prevent this, a better quality analogue meter with a built in mirror to prevent parallax could be used to my advantage. - Also, if I had more time I could have extended my experiment and repeated it with shorter intervals of wire. I could have taken readings every 5cm instead of every 10cm, this way I could gather more information and add a set of supplementary details to my results. If I changed all of the above, in theory I should come across far superior accuracy in my readings. If this theory is correct my results graphs should show a stronger correlation. If I were to present extra evidence I could make the following changes for further experiment. - Increase length of wire - Increase the thickness of the wire, - Change the material of the wire. If the above three changes were investigated for further experiment, I would hope that they would only validate my predictions and basically back up my evidence. By: Luke Stokes ...read more.

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