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Investigation To See If the Length of Any Type of Wire Affects Its Resistance.

Extracts from this document...

Introduction

Investigation to see if the length of any type of wire affects its resistance.

Introduction:

Resistance is a force. It opposes the flow of an electric current around a circuit. A circuit itself can resist the flow of particles if the wires are either very thin or very long. E.g. the filament across an electric bulb is very thin, as it needs to resist the flow of particles so that the bulb can glow.

Resistance is measured in ohms. This discovery was made by George Ohm. He found out that the voltage of a circuit is directly proportional to the current flowing through the circuit. It means that if the voltage is doubled then the current is also doubled. . He also discovered that a circuit sometimes resists the flow of electricity. He called this resistance. He also made a general rule for working out the resistance of a circuit:

V/I = R

V - Volts

I - Current

R - Resistance.

Extra Information:

Before starting my coursework I have decided to write down the factors that will affect the resistance of a wire. Below is a list of factors and reasons why they affect the resistance of a wire. To explain the how the factors would affect the resistance of a wire I have drawn a diagram to show how resistance occurs.

WIRE=

ATOMS=

ELECTRONS=

Middle

3.85

10.13

90

0.36

3.89

10.81

95

0.32

3.92

12.25

100

0.31

3.94

12.71

Figures have been rounded off to two decimal places for the resistance.

Observations:

1. I observed that the reading on the voltmeter and ammeter change as we change the length of the wire. The voltage increases as the length of wire we use increases.
2. The range of current was quite high in the beginning. From 10cm to 50cms the range was 1.28amps. From 50cms to 100cms, the range was only 0.28

Evidence: to make sure our overall values are as accurate as possible we will repeat our readings once more and then take the mean resistance of the 2 readings. I will also be able to spot any anomalies from our results.

Results:

 Length (cm) Current (I) Voltage Resistance (ohms) 10 1.85 2.35 1.27 15 1.48 2.72 1.84 20 1.15 2.95 2.57 25 1.00 3.18 3.18 30 0.87 3.34 3.95 35 0.75 3.45 4.60 40 0.70 3.48 4.97 45 0.62 3.63 5.86 50 0.57 3.68 6.46 55 0.51 3.69 7.24 60 0.49 3.76 7.67 65 0.45 3.80 8.40 70 0.45 3.80 8.40 75 0.42 3.82 9.10 80 0.40 3.84 9.60 85 0.36 3.85 10.69 90 0.34 3.89 11.44 95 0.30 3.92 13.10 100 0.29 3.94 13.59

To check to see if my prediction was correct I performed a test with another type of wire. This wire was thicker than the nichrome wire so it should have a lower resistance than the nichrome wire. The apparatus and the circuit diagram are the same as shown for the previous wire.

Table of results. The experiment was performed twice to make the readings more accurate.

 Length (cm) Current (I) Voltage Resistance (ohms) 10 20 30 40 50 60 70 80 90 100

Conclusion

The accuracy for this experiment is, theoretically, ± 15.7%, but as one can see this does not seem to be the case from looking at the graph. The reason for this could have been due to a number of different factors. Firstly the temperature of the wire was not necessarily 20C when we conducted the experiment and the material of wire may not be as pure as it should have been. The main reason for this was probably due to the equipment that we used being inaccurate. This did not stop us from seeing the trend, though, because the equipment would have been out by a constant amount each time therefore there was a constant error. So the trends that were predicted in the plan still were shown. Also I do not feel that the crocodile clips were always fixed securely to the wire with a good connection. This also meant that they were easy to move about on the wire changing the length of it. Errors rarely occurred in the setting of the current and the reading of the voltage.

The crocodile clips and the connecting leads could have affected the fairness of the experiment. They are a different type of metal from the Nichrome wire and may have different properties and therefore different resistance. Therefore the resistance of the Nichrome wire showed up on the multimeter was slightly more than it actually was.

Mean table of results for nichrome wire.

 Length (cm) Mean Current (I) Mean Voltage (V) Mean Resistance (ohms) 10 1.865 2.35 1.265 15 1.475 2.71 1.84 20 1.165 2.95 2.535 25 1.00 3.18 3.18 30 0.87 3.34 3.89 35 0.76 3.445 4.54 40 0.70 3.48 4.97 45 .625 3.63 5.815 50 0.58 3.68 6.24 55 0.51 3.69 7.24 60 0.49 3.76 7.67 65 0.45 3.795 8.41 70 0.45 3.80 8.42 75 0.425 3.82 9.00 80 0.405 3.84 9.485 85 0.37 3.85 10.41 90 0.35 3.89 11.125 95 0.31 3.92 12.675 100 0.30 3.94 13.15

Mean table of results for thicker wire.

 Length (cm) Current (I) Voltage Resistance (ohms) 10 20 30 40 50 60 70 80 90 100

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