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Investigating the Resistance of Wire.

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Physics Coursework: Investigating the Resistance of Wire

Resistance can be defined as an opposition to current flow. It can be calculated using Ohm’s Law;

Resistance (Ω) = Potential Difference (V)

Current (A)

This law will hold as long as the temperature of the wire is kept constant

The value of the resistance of a wire will depend on a number of different factors: The length of the wire; the cross-sectional area of the wire; and the material the wire is made out of.

Length of the Wire

The longer the wire, the greater its resistance. Without a potential difference, the free electrons move at random throughout the wire. A direct current causes the electrons to flow in a set direction. As they move, they

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Material of the wire

Some materials are better conductors than others for a number of reasons. They may have a larger number of free electrons per volume than other materials. These free electrons are available to carry current when a potential difference is applied to the ends of the wire. In addition, the size and closeness of the remaining ions may contribute to conductivity. Metals such as copper are very good conductors and will have a low resistance. The measure of a material’s resistance for a given length and thickness is its resistivity (ρ). The units of resistivity are Ωm.


I predict that doubling the length of the wire will double the number of collisions an electron has with the ions. Therefore, the resistance is doubled.

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Ammeter (accurate to 2d.p. or ±0.005A), 2 Crocodile clips, Meter rule, Power pack, Voltmeter, Switch, Wire (varied in length)

Circuit diagram


From the results of this investigation, it is proven that the resistance of wire increases, or becomes greater, when the length of the wire is increased and no other variable is changed at the same time.


There are a few things that could have affected the results, and perhaps given false results, during this experiment. For example, if one of the group cut the wire too short or too long, this would not give the correct result for say 80cm. Also, if someone misread a result and recorded it under the wrong measurement, that would affect the graph. If the wire was bent this would affect its resistance.

All these factors could have potentially made the results void.

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This student written piece of work is one of many that can be found in our GCSE Electricity and Magnetism section.

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