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To investigate how current affects the resistivity of a wire.

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Introduction

To investigate how current affects the resistivity of a wire. Planning Aim: the aim of this experiment is to investigate how current affects the resistivity of a wire. Discussion: atoms are made up of a positively charged nucleus surrounded by negatively charged electrons. In solids one or two of the outer electrons in each atom are used to bond with atoms that hold the solid together. In a metal these electrons are free to move throughout the solid to anywhere they want. These are usually known as "de-localized free electrons". An electrical current is a flow of charged particles and therefore the free electrons can flow through the metal if a voltage is applied to the metal. The resistance of a wire is where a metal wire is placed in an electric circuit and the voltage from the battery makes the electrons flow through the wire. They collide with metal ions whilst doing this and this process slow down the flow. Therefore resistance is the measurement of how easily the electrons can move through the metal- a low resistance means that the electrons can move easily and a high resistance means that the electrons cannot move so easily. The current is the measurement of how much charge flows per second. I=Q/t Current represents the number of electrons flowing per second, as the charge on each electron is the same. If the resistance is high ten the flow of electrons is slow and therefore the number of electrons per second is reduced, i.e. the current is reduced. If the metal is heated the metal ions will vibrate more thus there is a greater chance of an electron colliding with a metal ion and so the flow of electrons is reduced. (I.e. the resistance increases) The most common analogy is that if you consider yourself to be an electron and are walking through a crowd of people (the metal ions). ...read more.

Middle

Conclusion

I kept the cross-sectional area of the wire the same throughout the entire experiment to also help make it a fair test. I did this by using the same piece of wire for each measurement. In not changing the wire I also kept the resistivity of the wire the same as the material of the wire could not and did not change. If you look at the graph for my initial readings you can see there's one anomalous result. This is occurs when the length of wire is 20cm. The anomalous result could have happened because either the wire may have been over heated for that particular reading, hence the resistance increases, or, the result may have been misinterpreted due to human error, i.e., I may have recorded the incorrect reading from the ammeter or put the crocodile clips on the wrong length of the wire. However in spite of this minor setback and despite these problems this experiment provided me with good enough results. I could have repeated the experiment even more times for even greater reliability. From my results I was able to produce accurate graphs and the points on these graphs are close to the line of best fit on the graphs. However, an investigation can always be improved upon and I feel I could improve my investigation by: 1) Using a digital ammeter to reduce human error. 2) Leaving the wire time to cool down between readings to help make it a fair test. 3) A longer wire 4) Water bath 5) Higher voltage 6) Variable resistor 7) Volt meter after power pack In my opinion my results were sufficient enough to form a good conclusion. I took 50 readings in total. All these points on my graphs are close to my line of best of fit, apart from my anomalous result, so I think I am right in saying that my results are accurate and can support my conclusion. ...read more.

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