## Learn more physics!

*Most recent answer: 07/10/2017*

Q:

Frankly I wasn't sure if this was a crank question or deeply profound, I'll let you be the judge.I've been an electronics hobbyist all my 50 years, and I've used resistors, capacitors, and less often inductors. How many different types of passive electronic components are possible? I searched for and found something called a memristor which apparently IS a brand new kind of component that behaves differently than any of those. Wikipedia has a diagram here:https://en.wikipedia.org/wiki/Memristor#/media/File:Two-terminal_non-linear_circuit_elements.svgI'm curious, there are components on all the outside edges, what about the diagonals, what do these represent? They have different equations so they MUST behave differently, what ARE these components?

- David Kaye (age 50)

Minnapolis, MN USA

A:

The memristor is a *non-linear* circuit element. In principle one can imagine an infinite variety of non-linear elements with different types of non-linearity.

Resistors, capacitors, and inductors are *linear* elements. Linear elements must have response consisting of current in-phase with voltage or ±90° out-of-phase, or some linear combination. That leaves only three possibilities. You might imagine a fourth possibility, with current 180° out-of-phase, but that would dump energy into the circuit instead of dissipating it. In thermal equilibrium, that would violate thermodynamics. So, at least at any one frequency, resistors, capaciitors, and inductors are all you need.

Mike W.

*(published on 07/10/2017)*

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