I should note that my statements below may be FOC; I do not myself have a CS or EE degree, so take what I say with a modicum of salt...
But first, note that I wrote "function", not "circuit".
It could be argued that CS, on the whole, is a subset of mathematics, particularly that of boolean algebra and logic. As such, the functional equivalency between the abstract of boolean logic/algebra, and its implementation on a physical substrate, could be considered among the most important of CS concepts.
One could also argue (maybe?) that Turing's "equivalency theorem" might be related to such as well. Consider the case of an emulation of hardware done in software; one could consider that - at a base level, it is boolean logic expressed physically, being expressed equivalently as boolean software functions.
The opposite it also true, of course - that it is possible to express software boolean functionality in the equivalent physical form.
What form it physically takes does not matter (other than speed of course), which is why I also didn't ask for an implementation/representation in electrical terms or schematic form, but rather a diagram of something that could be expressed as a physical and mechanical object. If the person were so inclined, they could express it as a series of levers and marbles, or in LEGO, or Meccano, or any other similar option.
EE knowledge is not needed here, I don't believe (Martin Gardner might agree).
did you talk like this to the CS masters, no wonder they left