Resistivity

Intermediate

A material property independent of shape.

Key relationρ = RA/L

ρ is a property of the material: copper 1.7×10⁻⁸ Ω·m, nichrome 1.1×10⁻⁶, glass 10¹⁰ or more. It's independent of the wire's size.

Worked example

Heating elements use high-ρ alloys.

Common mistake

Don't mix resistance and resistivity.

In more detail

Resistivity ρ is a material property defined by R = ρL/A. It describes how strongly a material resists current, independent of its shape.

Choosing materials for cables, heating elements and resistors.
Copper's low resistivity makes it ideal for wires.
Engineers choose copper for wires and nichrome for heating elements because their resistivities differ greatly.

What units does resistivity have?

Ohm metres.

Why is resistivity important?

It lets you compare materials regardless of the size of the component.

Does resistivity depend on the size of a wire?

No. It is a property of the material, while the resistance also depends on length and cross-sectional area.