# To find out if and why wire lengths give resistance - To find out if the wires obey Ohm's Law.

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Introduction

Resistance Coursework

Ben Sweeney

Aim: 1) To find out if and why wire lengths give resistance

2) To find out if the wires obey Ohm’s Law.

Prediction: I predict that the three lengths of wire (200mm, 400mm, 600mm) will all obey Ohm’s Law, and each will put up a resistance. Resistance is when a component in an electrical circuit prevents electric currents from flowing as quickly as they could, the electrons are all compact and it takes longer for and electrical current to get by. Ohm’s Law states that, “for any given conductor at a constant temperature the current (the flow of electricity) in it is proportional to the applied voltage (the force that the current is pushing at)”^{[1]}, meaning; for any component in an electrical circuit the resistance will always be the same for it, no matter what the voltage is. I predict that the wire will obey Ohm’s Law, and the longer the wire the higher the resistance will be. I think this is because a wire is long and thin and constricts the movements of electrons, like too many people in the corridor. The electrons will keep bumping into each other and the longer the wire the longer it’ll take for the electrons to get through. So for the shorter wire the electrons will squeeze through quicker.

Middle

1.13

0.34

3.32

2.46

0.88

2.8

2.49

0.89

2.8

1.88

0.58

3.24

2.83

1.01

2.8

2.79

0.99

2.82

2.52

0.77

3.27

3.18

1.13

2.81

3.09

1.1

2.81

3.15

0.97

3.25

3.53

1.26

2.82

2

1.42

1.41

3.55

1.1

3.23

Table to show the current and voltage put through a 400mm wire and the resistance it gives

first test | first repeat test | second repeat test | ||||||

Voltage (v) | Current (a) | Resistance ( r) | Voltage (v) | Current (a) | Resistance ( r) | Voltage (v) | Current (a) | Resistance ( r) |

1.21 | 0.62 | 1.95 | 1.18 | 0.62 | 1.9 | 1.17 | 0.62 | 1.89 |

1.57 | 0.81 | 1.94 | 1.52 | 0.8 | 1.9 | 1.51 | 0.8 | 1.89 |

1.86 | 0.96 | 1.94 | 1.8 | 0.94 | 1.91 | 1.82 | 0.96 | 1.9 |

2.11 | 1.09 | 1.94 | 2.08 | 1.1 | 1.89 | 2.09 | 1.11 | 1.88 |

2.36 | 1.22 | 1.93 | 2.31 | 1.22 | 1.89 | 2.31 | 1.23 | 1.89 |

2.63 | 1.36 | 1.93 | 2.54 | 1.34 | 1.9 | 2.56 | 1.35 | 1.9 |

Table to show the voltage and current put through a 200mm wire and the resistance this wire gives

first test | first repeat test | second repeat test | ||||||

Voltage (v) |

Conclusion

Wire length: | |||||||||||

First test | First repeat test | Second repeat test | Third repeat test | ||||||||

Current (a) | Voltage (v) | Resistance ( r) | Current (a) | Voltage (v) | Resistance ( r) | Current (a) | Voltage (v) | Resistance ( r) | Current (a) | Voltage (v) | Resistance ( r) |

Turn the powerpack on and move the dial to the first mark. In the first test section jot the results for the voltage and current from the ammeter and voltmeter. Move the dial onto the next mark and take the results again. Repeat this task again until it has been done seven times in total. Turn all the equipment off and let it cool down for a minute or two. Turn the powerpack back on and repeat the test three more times until the whole table is filled.

With the other three tables repeat all said in the last paragraph for the last three lengths of wire (400mm, 600mm, 800mm).

Having four sets of results for each length of wire , work out the average resistance and plot a scatter graph for each collection of results using the averages. All the marks, if Ohm’s law is unaffected by the magnets presence should be on the line of best fit.

[1] Extract from The physical World by Ken Dobson, published by Nelson

This student written piece of work is one of many that can be found in our GCSE Electricity and Magnetism section.

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