Investigating the Resistance of Wires

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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:

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In a larger diameter, there

[IMAGE][IMAGE][IMAGE][IMAGE][IMAGE][IMAGE][IMAGE][IMAGE][IMAGE][IMAGE][IMAGE][IMAGE][IMAGE][IMAGE][IMAGE][IMAGE][IMAGE][IMAGE][IMAGE][IMAGE][IMAGE][IMAGE]Figure

1: are more routes for free

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electrons to travel

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through.

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In a smaller diameter,

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2: there are fewer routes

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for the free electrons

[IMAGE] to travel through.

Plan:

I will set up a circuit consisting of a cell, ammeter, voltmeter and

50cm of constantan wire. The diameters I will use are as follows.

0.56mm, 0.43mm, 0.38mm, 0.32mm, 0.27mm and 0.20mm. I will measure

these diameters with a micrometer. I will take three readings of the

current and potential difference for each different diameter of the

wire and take an average for V (potential difference measured by a

voltmeter) and I (current measured by an ammeter) in order to get the

most accurate results possible. I will then plot these results in two

graphs one plotting V against I and another plotting the average

resistance (using ohm's law R=V/I) against the diameter.

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