A Level Physics CURRENT ELECTRICITY Resistance, resistivity and conductivity.

RESISTIVITY
The resistance of a ohmic material is only constant for a given length and shape, therefore a value for resistivity of a material is more useful as it allows the resistance of all sizes and shapes to be calculated. If the resisitivity of a material is p then

R = p L / A
where L is the length and A is the cross-sectional area. The conductivity is a measure of conductivity and is the inverse of resistivity ( 1 / p ).
To determine the resistivity of a material a know length and diameter would be compared with a resistor of know resistance on a potentiometer.

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Rob Coles 27 May 1996 15:23:19