One of my favorite things to point out to friends of mine is this fact:

Remember in Back to the Future (I, II, and III) Doc Brown used a “flux capacitor” to travel through time?  Well, what if I told you that every capacitor is a flux capacitor?

Well that’s true.   As a simple example, say I took a capacitor and hooked it up to a battery, as below.  Then I show the capacitor as two metal plates with electric field between them, and a surface “S” parallel to the two plates.

fluxcapacitor.JPG

As this crude analysis points out, the flux is nonzero so long as the voltage across the capacitor – any capacitor  – is nonzero.

Movie fans will point out that this isn’t magnetic flux, to which I have two rebuttals:

1.) the movie never states whether Doc Brown means electric or magnetic flux

2.) fine, you want a magnetic flux capacitor?  I give you, the mystical LC network – the transmission line stub, the antenna, the cavity resonator…etc.

Sorry Robert Zemeckis.