Electricity - Resistivity

Question 1

Resistivity

Answer 1

• Resistivity is a property that describes the extent to which a material opposes the flow of electric current through it
• it is a property of the material itself, not the size or shape of the sample.
• It usually depends on temperature and may depend on other quantities such as pressure.
• The resistance of a piece of material depends on its resistivity and also its size and shape.
• The equation for Resistance using resistivity is:
Resistance = (Resistivity * Length)/Cross-sectional Area
• The unit of resistivity is the ohm metre.

Question 2

Resistance of a wire

Answer 2

• When current flows through a component, the resistance depends on the geometry of the component (length and cross-sectional area) as well as property of the material (resistivity).

Question 3

Temperature Dependence of Resistivity

Answer 3

• Resistivity also depends on the temperature of the material. At a constant temperature, we can assume that the resistivity is a constant.
• In metal conductors, when the temperature increases the resistivity also increases
• In thermistors, increasing the temperature decreases the resistivity, however this is not in a linear manor, as resistivity decreases a lot for a small temperature increase.
• In Superconducting materials, the resistivity is always zero, as long as the temperature does not increase past the critical temperature, the resistivity will stay at zero.