Measuring the Resistivity of Copper Wire of Different Lengths

Topics: Measurement, Resistivity, Copper Pages: 11 (3795 words) Published: March 24, 2013
Measuring the Resistivity of Copper Wire of Different Lengths In this report I will be writing about the experiment I will conduct on copper wire of different lengths. The dependent variable I will be measuring is the resistance of the Copper wire. To do this experiment, one needs to obtain measurements with a high degree of accuracy, taking care of the equipment they use and measuring each value to a certain degree of accuracy for all results. The problem with measuring the resistivity of Copper wire is due to the properties of copper as a material. Copper naturally has a low resistance due to it being a superconductor, meaning that it only has a resistance of minute amounts. As it has this property, it is important to use a copper wire specimen that is long enough and thin enough to have an appreciable resistance. The normal value for the resistivity of copper is about 10-8Ωm. A 1m length of copper wire with a cross sectional area of 1mm² (10-6m²) can be predicted to have a resistance of 0.01Ω. This can be calculated by using the resistance formula of: R=ρlA≈ 10-8 Ωm x 1m10-6m2=10-2Ω

The wire I will use is going to be thinner than this and will vary in length from 0.2-1.0 metres with a difference of 0.2m from the previous wire specimen. In total I will have 5 different lengths. Apparatus:

* Voltmeter- Accuracy stated as (± 0.5% Read. + 1dgt) in the user manual * Ammeter- Accuracy stated as (± 1.2% Read. + 1dgt) in the user manual * Battery Supply of 6V
* Copper Wire
* 1m Ruler in cm
* Scissors
* Electrical Wires
* Crocodile clips
* Micrometer

The following procedure described below is how I intend to gain my results: 1. I will measure out the different lengths of copper wire I intend to use using a millimetre ruler to gain the most accurate results I can. 2. Once the lengths are cut, the diameter of the copper wire I am using must be measured. To gain the most accurate result, I will use a micrometer and measure the diameter in several places on the wire and take an average value from these readings to work out the average cross sectional area. 3. I will connect the first length of wire into an electrical circuit, making sure that current can flow through the entire length of the copper wire connected. The circuit will look like this diagram:



4. The voltage will be recorded across the wire and the current running through it. 5. To find the resistance of the wire I will use the formula V=IR. 6. The resistivity can then be worked out using the formula: ρ=RAL where R is the resistance calculated, A is the cross sectional area of the copper wire calculated and L is the length of the copper wire. The measurements shall be recorded in the following table shown below:

Resistivity of Wire
The physical properties of a wire can either be categorised as being an intrinsic property or an extrinsic property. The difference between the two categories of properties is that intrinsic properties do not depend on the amount of material that is present, whereas extrinsic properties do depend on the amount of material that is present. In the following investigation of the resistivity of copper wire, one could say that the value of the voltage, resistance and current are all intrinsic properties of the copper wire. The extrinsic value of the copper wire would be its resistivity. The resistivity of the copper wire will be dependent on the material itself, which is copper. The resistivity of a material can be defined as the resistance of a 1m length with 1m² cross-sectional area. As the resistivity of material depends mainly on the properties of the material itself, each material whether it is copper or pure silicon has its own resistivity coefficient. The coefficient for copper is 1.72 × 10-8Ωm. This value may seem very small for resistivity, but if one were to know that copper is classed as a superconductor meaning that it conducts electricity extremely...
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