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To investigate how the diameter of a constantan wire will affect its resistance and hence the current flowing through it.

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Introduction

Investigating the Resistance of Wires Aim: To investigate how the diameter of a constantan wire will affect its resistance and hence the current flowing through it. Prediction: I predict that the thicker the diameter the less resistance there will be. Reason: In a metal, some of the electrons are free to move between the ions, to form a "sea" of electrons around the positive metal ions. Metals that are good conductors have more "free" electrons and therefore these electrons move easily around the positive metal ions. However in metals that have fewer "free" electrons, the ions act as obstacles to the flow of electrons and therefore the wire has resistance. The current becomes stronger with the more electrons that flow through a wire in one second. As the diameter increases the electrons will have more available routes between the ions to pass through per second, making the electron flow greater hence the current becoming stronger. See figures 1 and 2: In a larger diameter, there Figure 1: are more routes for free electrons to travel through. ...read more.

Middle

I will keep the wires the same length, use the same type of wire and make sure the wires are always room temperature. To do this I will make sure the wires have cooled down from their last use. I will achieve this by leaving 2 minutes between each experiment so the wire can cool down. I will use a micrometer will be used to measure the diameter of the wires. Diagram: 50cm Constantan wire. A V Crocodile Clips Results table and graphs: See graph and result table pages. Conclusion and Analysis: My results show that as the diameter is increased the potential difference (V) decreases, the current (I) increases and the resistance (V/I) decreases, showing that when the diameter is increased the resistance is lowered and therefore the current is increased. I can see this from my results table, looking at the averages. On my graph I plotted the diameter against the resistance the points plotted produce a curve of best fit, showing that the diameter could be indirectly proportional to the resistance of the wire. ...read more.

Conclusion

This was the reading for V / I on the 0.43mm wire on my graph. It did not fit the curve of best fit. This inaccuracy could have been caused by human error, by which I misread the voltmeter and/or the ammeter or the connections in the circuit were faulty. I also had an anomalous result in my results table which did not fit the pattern and is not anywhere near the previous experiments. I repeated this reading and found the true result. After performing the experiment I feel diameter was not a good variable to choose, as the wire is three dimensional, with an uneven range which was out of my control. Due to the wire being 3 dimensional, the free electrons flow through all the routes in the area of the wire, so a relationship between the resistance and the area of the wire is more likely than a relationship between the diameter and the resistance. To extend my investigation I could calculate areas of the cross section of each wire and plot a graph to find out R x I/A. Kimberly Williams Physics Coursework 1 ...read more.

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