## Resistivity and Conductivity

### Gap-fill exercise

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There are three factors in determining the resistance of a wire:
• Its length;
• Its ;
• Its material.

The resistance is proportional to the length, and proportional to the area. The property of the material is the .

The diameter is measured using a screw gauge. It gives us the diameter in . However, the area in the formula is in square metres.

To convert square millimetres to square metres, we have divide by .

Conductivity is also a property of the material. It is worked out by the equation = 1 ÷ resistivity.

When the temperature is very low, the resistivity gets very low. If the temperature of some materials is low enough, the resistance is . The temperature has to be below the temperature, otherwise super-conduction does not happen.