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The Electrical Resistance of a wire

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Introduction

The Electrical Resistance of a wire

Resistance

To understand electrical resistance in a wire, you must first understand how the wire is able to conduct electricity. In metal atoms, the electrons in the outer shell are loosely attached. These electrons float around in a “sea” of electrons. This is called metallic bonding. This explains why metals can conduct electricity so well. So when electricity is passed to one part of the metal, the electrons quickly carry it to all the other parts. The conductivity of a solid will depend on the density of free electrons and how easily they move. Resistivity depends on how difficult it is for electrons to move through a medium. Atoms are arranged in “ energy bands”. The lower band is called the valence bad and the higher band is called the conduction band.  For electricity to flow, the electrons gathered at the lower bad must flow to the conduction band, where they are free to flow to make an electrical current. Resistance is how hard it is to move electrons through a medium. When travelling electrons in a wire collide with the atoms of a wire and other obstacles, such as impurities. The collisions between the electrons and atoms cause the electrons to move slower, which causes resistance.  

Aim

I aim to plan and carry out an experiment, which shows one variable that affects the resistance of a wire.

Planning

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Middle

2)Proportional to 1/A (where A is the area of the cross-section of the wire)

We can then, therefore create an equation for the resistance of each wire in terms of a constant of proportionality called Resistivity.

R=PL/A

Where  R=resistance

P=Resistivity of the metal

L=length

A=area of cross-section

With this equation, we can work out why copper is used for wires, as its Resistivity is very low. The electrons will move towards the positive charge, when an electrical potential is applied, as like charges attract. Electricity will flow from the negative terminal to the positive terminal. The electrons are the charge carriers that carry electricity through the circuit.

Method

Equipment:        Power Pack

                Voltmeter

                Ammeter

                Wires with crocodile clips/croc and plug clips

                Reel of wire

                Scissors

                Micrometer

                Calculator

                Ruler

                Stopwatch

Circuit

I will take the wire and cut a 10cm strip with the scissors. I will be extremely careful when trying to cut the wire, as it’s sometimes a struggle. I will set up a circuit like the one above. I will connect the wire to the circuit to act as the resistor. I will make sure that the ammeter is connected in series and the voltmeter is connected in parallel. I will set the power pack to direct current D.C.

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Conclusion

   There is also my rounding in my figures to a suitable degree of accuracy, which in this case, is to two decimal places. I feel this to be of appropriate degree of accuracy, as the voltmeter only reads to an accuracy of two decimal places. I also had to read an ammeter with a dial, so when reading the reading, it was of my own judgement, and this was not reliable. I therefore to improve the experiment, I will use a digital ammeter in my circuit. When working out my averages, I think I could use the not rounded off figures to calculate the resistance, to make my results more accurate.

   To improve my experiment next time, I think I would use wire length no smaller than 10cm, as then I could perhaps increase the voltage, to see if that makes any difference. A length smaller than 10cm with a higher voltage than 2V would overheat making the temperature of the wire increase and increasing the resistance. I would perhaps next time, make the width as my variable and the length as my constant and see how the width will affect the resistance of a wire.  

...read more.

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