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An experiment to find the resistivity of nichrome

Extracts from this document...

Introduction

An experiment to find the resistivity of nichrome A. Planning Plan of the method to be used: - The resistivity of nichrome can be determined using the equation ??=?RA/L Where: R:- Is the resistance of the wire in ?"ohms" and can be determined using the equation R=V/I where "V" is voltage in volts and "I" is current in Amperes. L:- Is the length of the nichrome wire used in metres. A:- Is the cross-sectional area of the wire in metres square and can be determined using the equation A= ??d2 where "d" is the diameter of the wire. If I plot a graph of length on the x-axis against resistance on the y-axis. From the relation R = ? L /A which corresponds to the st. line equation ? y=mx the graph should be a st. line passing through the origin where "m" is the gradient of the st. line graph and corresponds to ?/A. Since the cross-sectional area of the wire can be found by knowing it's diameter. Therefore the resistivity of nichrome can be calculated. ? Diagram of the circuit used in this experiment List of the apparatus used: - 1- Power pack supply of 4V 2-A variable resistor 3-A full scale deflection ammeter with a measuring range of 0-1 A 4-A digital voltmeter with a measuring range of 0-5 V 5-P, Q represents terminal blocks. 6-Circuit wires 7-PQ=Nichrome wire 8-A meter ruler 9-Michrometer screw-gauge 10-Sellotape Detailed method: - I set up the circuit as shown in the diagram that I have drawn. I started the experiment by taping a meter ruler between the terminal blocks P, Q so that I could measure 100cm of nichrome wire. I made sure that the wire was carefully tightened at both terminals to try to minimise the kinks or twists in the wire. I then switched on the power pack supply and adjusted the variable resistor until a constant current of 0.2A was flowing through the circuit. ...read more.

Middle

5 10 15 20 25 30 35 40 45 50 This will investigate the value of varying the length of the wire. The repeat results will be produced in a graph similar to this. I will need a ruler, different metals and an instrument to measure the surface area of the wire. I will also need a voltmeter and an ammeter. The equipment will be set up in the following manner as shown in the circuit diagram so that I can measure the voltage readings and ammeter readings for each length and wire. I will vary the Wire by placing a crocodile clip at different lengths down the wire in order to vary the lengths. I will use the results of the investigation to answer the question by placing the results into a chart and then transferring the information onto a graph so that is easy to interpret. We can see that if my prediction was correct because we can see that there is a direct proportionality between the factors and the resistance. Other work and preliminary work that I have done that will help me in this experiment is that How the length of a wire changes the resistance The resistance of a wire depends on certain factors. Investigate the effect of two of these factors - Planning Some variables that will be relevant to this investigation are: * Length * Thickness * Temperature * Voltage * Resistance * Material Of these the variables will be input and output voltages in experiment one, and length and resistance in experiment two. The other variables (temperature, material and voltage) will have to be kept constant in both experiments to make sure that only length, thickness and resistance are investigated. In experiment 1 the same bit of wire and the same thickness need to be kept constant. In experiment 2, the length will need to be kept constant to make sure only the variables indicated are investigated to ensure a fair test. ...read more.

Conclusion

Evaluation From my results table and graph I can see that my results that I collected are very reliable. I know this because my results table does not show any individual anomalous results this means that I did not have to leave any results out of my averages because they were anomalous. Also on the graph I can see that none of the averages plotted are anomalous because all the averages lie along the same straight line. During my experiment I have noticed several modifications I could make to improve on the Investigation if I was to repeat it. The first of these modifications would be the circuit that I would use. To be more accurate with my results I would use the circuit layout below: POWER SUPPLY 2 VOLTS AMMETER VOLTMETER WIRE METRE RULER Instead of connecting the voltmeter to the main circuit I would connect it to the wire which is being tested. I would do this so that the voltmeter is measuring the voltage of just the wire being tested and not the wires of the main circuit as well. To also improve on my results I would use a digital voltmeter instead of an analogue meter. I would do this because a digital voltmeter is a lot more accurate than an analogue because if the needle in the analogue voltmeter is bent then the readings given off will be false whereas a digital voltmeter does not rely on a needle or any other manual movements. The next modification I would make would be to use pointers instead of crocodile clips , I would do this because pointers would be more accurate. The pointers would be more accurate because the tips have a much smaller area than the crocodile clips giving a more accurate measurement of the length of wire. As well as making these modifications I would also improve my Investigation by testing the same wire but different widths of that wire. I would do this to expand on my Investigation. 1 1 ...read more.

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