OK. EMP 101, exam review.

EMP is a burst of electromagnetic energy, similiar in concept to what is happening an microwave or right next to a radio transmitter. When the electromagnetic waves strike metal (or any other conductor), they are converted into electricity.

That electricity is a very fast, very short, very sharp spike. It can damage a vacumme tube, at demonstrated at the only high altitude nuclear bomb test at Bikini, which blacked out much of Hawaii's radio transmitters until parts can be ordered. That being said, tubes are much more robust than transistors and integrated circuits. An old style, stand alone transistor is more robust than a modern IC containing thousands or millions or billions of transistors. The reason for this is, the smaller the widget, the more readily smoked by the EMP.

A device which is unpowered is less likely to be damaged, as you only have W(EMP) going through the circuit rather than W(source) + W(EMP). As a result, you are less likely to overload the components, but the statistical difference is very, very tiny unless you are pulling hundred of watts- most things that really matter live off less than then enough to be effective. (Please note that the computers that control the power grids have the same power requirement as you household PC- 12V or less at varying milliamps.) You have to worry about both the voltage and the amperage- remember, volts hurt, amps kill.

As a result, anything with integrates circuits (including some lithium batteries) will be smoked even unpowered, unless heavily shielded. Yes, taking the batteries out helps, so does bailing with a coffee cup when the boat is sinking. Yes, turning it off helps, so does bailing with a soup spoon.

Simple transistors, like LEDs, might survive. Powered tubes, might survive. Unpowered tube probably will survive unless they are too close. Problem, we haven't made tubes in this country for over 20 years, and even the last factory in Russia is shut down most of the time due to lack of demand.

If we are talking widespread EMP, we are talking TEOTWAWKI. And no more wrist watches unless you have one that winds.