# The resistance of copper wire.

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Introduction

PHYSICS AS COURSEWORK

NAME: Rameez Ali

TITLE OF EXPERIMENT The resistance of copper wire

To find out the resistance of copper wire and to work out the resistivity of the copper wire you can use the following equation: R=ρl

A

PLAN

Diagram | A2b for partial A4c for complete, correct, labelled (including dimensions) (correct circuit diagram where appropriate) |

List of apparatus Here are the tools and equipment we will be using: Power pack (12v dc max.), used voltage: 2v, Metre ruler stick (1000mm length), Copper wire – (cross-sectional area= 0.31mm), Ammeter (5amps, >0.2A), Volt meter (20 volts, >0.1v), Micrometer (>0.01mm), blue tack, crocodile clips, heatproof mat. | A2d for some A4d for all A6d for all with full specifications (eg instrument ranges) |

Input (independent) and output (dependent) variables Input- The length of the copper wire. Output- The voltage and current readings. | A4b for one of each |

Control variables (to be kept constant) The cross-sectional diameter of the copper wire will be kept constant throughout the experiment to ensure a fair test. Also, the type of wire used will be kept the same, (wire used=copper). | A6a for one |

Method First of all you will need to set up the apparatus in the correct order as shown in the diagram. You will need a voltmeter, ammeter, battery pack (12volt) and six wires. You will then secure the wire to a metre stick ruler and make sure that there is a distance of 67cm between the two crocodile clips on each end – (1cm of space must be added on because of the width of the crocodile clips), this will bring the distance between the two clips to 65cm. To ensure the wire is secured to the ruler stick you would have to coil the wire around the ends of the stick, whilst doing this make sure there are no crossovers (to prevent the circuit from short-circuiting). You will the need to take eight individual readings from both the voltmeter and the ammeter; these should then be repeated to ensure accuracy and a fair test. After each of the readings is taken from the different lengths of wire the length of the wire will have to be shortened by 10cm each time (e.g. 50-40cm), however the last reading to be taken should be shortened by a length of only 5cm (e.g. 10-5cm). The thickness (cross-sectional length) of the copper wire was accurately measured to be 0.31mm. | A2a for outline plan A4a for detailed plan A6c for logical sequence |

Safety considerations To ensure safety whilst we are using the electrical equipment we will work away from areas where water is present (e.g. taps, containers and bottle etc.). Also we will make sure that the voltage does never exceed 6 volts as this will cause the wires to heat up and could present a safety risk. | A2c for anything appropriate |

Number and range of intended readings We will be taking 24 readings altogether (including repeats) and the range of length of the readings will be 65cm, going down 10cm after each reading is taken. | A6b for number and range |

Reasons for procedures based on scientific knowledge and understanding (eg why range or number or sequence of readings should give good or more accurate results) Through past experiments I have found that the resistance of a wire/circuit is greatly dependant on the length of the wire and also the thickness of the wire, overall I discovered that the longer the wire the higher the resistance – this is the main reason why we chose the length of the wire as our input variable as we knew that this would give variable current and voltage readings, also resistance. . As the electrons in an electric current move around a circuit, they bump into atoms in the metal wire in which they pass. Atoms of different elements impede the electrons by different amounts. Copper was used in the experiment because I know it is a good conductor of electricity and therefore has a lower level of resistance than many other metals | A8a for at least one valid reason |

Design justifications based on supporting theory (eg formulae and calculations) From my own scientific knowledge I can state that voltage (V) is proportional to current (I) – (provided that the temperature stays constant) and that the resistance of a wire or a circuit can be calculated using the formula: R=V/I. Therefore I predict that that the resistance of the wire will increase as the length increases because each electron must travel further throughout the wire and are therefore exposed to more ions and electrons within the metal which ultimately results in more resistance. I can also give a prediction that the thicker the wire the less resistance and the thinner the wire the greater the resistance. V=I x R. | A8b |

Middle

1.27V

0.28A

1.29V

0.30A

600mm

1.26V

0.31A

1.24V

0.32A

500mm

1.22V

0.35A

1.20V

0.37A

400mm

1.17V

0.42A

1.14V

0.45A

300mm

1.10V

0.55A

1.09V

0.58A

200mm

0.97V

0.71A

0.98V

0.70A

100mm

0.75V

1.06A

0.73V

1.07A

50mm

0.52V

1.50A

0.51V

1.47A

Average Voltage | Average current | Resistance (Avg.V/Avg.C) |

1.28V(700mm) | 0.29A | 4.41Ω |

1.25V(600mm) | 0.315A | 3.97Ω |

1.21V(500mm) | 0.36A | 3.36Ω |

1.155V(400mm) | 0.435A | 2.66Ω |

1.095V(300mm) | 0.565A | 1.94Ω |

0.975V(200mm) | 0.705A | 1.38Ω |

0.74V(100mm) | 1.065A | 0.69Ω |

0.515V(50mm) | 1.485A | 0.35Ω |

C2a: raw data recorded

B2b some readings made

B2c some readings recorded

B4b most readings accurate

B6b suitable precision

B4c at least 8 readings taken, with repeats

B8d mean values calculated

B2d two units correct

B4d all units correct

B6c clear and accurate presentation

C4b data presented with headings and units

B6a suitable sig. figs

Processed data

C2b equations used C2c p.d. recorded

C4a p.d. correct

A list of possible sources of random error

- Accidental adjustment of the voltage.
- Placing the crocodile clips slightly out of place.
- The crossing over of the wires.
- Faulty power packs, ammeter or voltmeter.

D2a

A list of possible sources of systematic error

- Faulty power packs, ammeter or voltmeter.
- The use of copper wire with a high level of impurities or long-term exposure to air.

Conclusion

D2d

Statement of theory related to investigation

Electrical resistance is the ratio of the potential difference (i.e. voltage) across an electric component (such as a resistor) to the current passing through it:

or

(where V is the voltage and I the current)

It is thus a measure of the component's opposition to the flow of electric charge. Electrical resistance is usually denoted by the symbol R. The SI unit for electrical resistance is ohm. Its reciprocal quantity is electrical conductance measured in siemens.

For a wide variety of materials and conditions, the electrical resistance does not depend on the amount of current flowing or the amount of applied voltage: the two are proportional and the proportionality constant is the electrical resistance. This is the content of Ohm's law.

As the length doubles the resistance doubles. Resistance is caused by electrons bumping into ions. If the length of the wire doubles, the electrons bump into the ions twice as much so the resistance will double.

The resistance of a wire at constant temperature depends primarily on its length, its cross-sectional area and its resistivity.

C8a

Written conclusion (with reasons) for what has been discovered

In an overall conclusion based on my predictions and final results, I have found that as the voltage decreases the current increases, and that resistance restricts the flow of electrical charge. Whenever there is a resistance present in a circuit, it will always restrict the flow of current; therefore making it smaller

C8b

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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