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This investigation discusses the aspects of wire resistance in a particular wire. I will be investigating the variable factors of wire resistance and setting up a simple circuit to test for wire resistance.

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Resistance of Wire

Aim:        This investigation discusses the aspects of wire resistance in a particular wire. I will be investigating the variable factors of wire resistance and setting up a simple circuit to test for wire resistance.


Everything on Earth is made of tiny building blocks called atoms. Inside atoms are smaller electrically-charged moving particles called electrons. It is the movement of these electrons that creates electricity. Some substances - especially metals - have electrons which can flow freely from one atom to another. The flow of electrons from one atom to another is know as an electric current, this is measured in volts (V). Metals such as copper and aluminium are particularly good at allowing the free flow of electrons and are known as conductors. These two metals are the ones most commonly used in electrical wiring. Resistance is how much the electrons don’t move and is measured in amps (A). The electrons in metals like copper move very easily so they have a very low resistance. Constantan as another example has a higher resistance because electrons in its atoms do not move as easily. The following diagram explains how this works.

The flow of electricity can also be explained by the following diagram.

Electricity on an atomic level


The atomic number of copper is 29, which means it has 29 protons in the middle and 29 electrons moving around the outside.

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•        Voltage applied (V)                                                         (Constant)

•        Temperature of wire                                                 (Constant)

I decided to use the length of the wire as the factor that I will change, this is because it will give the widest range of results.                                 I decided to test the resistance of wire using increments of 100mm of constantan. Constantan is an alloy metal made of copper and nickel. I will start at 100mm and go up to 1000mm on the same piece of wire to ensure a fair test and give a wide range of results.                         My reason for using constantan is that I already know it has a noticeable resistance. I know this from the research I did before conducting the experiment. It would not be a wise choice to use copper as the material of wire because copper has a low resistance therefore I would need to use very long pieces of wire before a noticeable change in resistance was visible.                                                                         The thickness of wire, or SWG, I will be using is 28 SWG. This is 0.375mm thick and should be the most suitable for this experiment.                The voltage I will be applying is 1 volt, according to the power pack. During the preliminary experiment the volt meter recorded a voltage of about 1.5 volts. If a too high voltage is applied then the wire will become very hot and affecting the resistance of the wire, using a too low voltage will not give accurate results.

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From my results I now know how I could have made it better and more accurate. To begin with I made the right decision to use digital meters. I chose digital not analogue so I could record exact results, rather than guessing the reading from a needle.

I chose a wooden ruler to measure with so I could be sure it would not short the circuit, meaning it would not make any connections between the wire and the ruler.

I didn’t however make the right choice of using crocodile clips to connect to the wire. The width of a crocodile clip is about 3mm, so when connecting it to the wire it could easily make results incorrect. The crocodile clip could be 3mm either way of each measurement. If some one was measuring it at 100mm it could be possible that the clip was at 97mm or 103mm. This makes all the readings unreliable. It would have been a wiser choice to use something with a point, so the width would be less than 1mm. This would make the results much more accurate and reliable.

The most important thing in the test was the wire. We carefully thought out what type of wire and what thickness it would be. But we only tested one strand of wire. As explained before the results were not exactly as expected. The wire could have had imperfections in the width of it. Or there could have been a kink or bend in the wire. If I was to conduct the experiment again I would do the experiment on about 3 or 4 different pieces of wire to ensure that results were accurate and unreliable.

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