Resistance, Resistivity & Sheet Resistance

You’ll often hear the terms resistance, resistivity, conductivity, sheet resistance, etc. thrown about. These are all related, and are different ways of answering this question:

How easy is it for electricity to move through the material?

There’s a detailed explanation here, but it’s pretty boring. Read on for the slightly-less-boring version.

Resistance (R [Ω])

What is it?

Resistance (R), measured in Ohms (Ω), tells you how much effort it takes to move electricity through an object — or, phrased differently, it tells you how much an object resists the flow of current.

How do we use it?

Primarily in Ohm’s Law, the workhorse of basic electronics calculations: If you know the resistance of a thing, you can get current at some applied voltage, or vice-versa.

How do we talk about it?

Resistance is specific to a single object.

GOOD:

“What is the resistance of this trace?”

“What is the resistance of this piece of wire?”

BAD:

“What is the resistance of copper?”

Why bad: This doesn’t mean anything. For this, you need resistivity!