EMP Q and A

I’ve gotten some questions in emails and comments on other sites regarding my EMP discussion. The science is all well and good, but give some practical advice!

See, there’s your problem. You know what we call the practical side of physics? Engineering. And it’s those engineers that build weapons of mass destruction and my orbital death lasers and the like, not physicists. Anyway, I’ll see if I can give more practical answers, but don’t hold your breath.

Does it matter if an electrical appliance is plugged in or not?

Ooh, good question. If you’ve got something plugged in, it’ll likely get more EMP. Power lines can act like antennas and conduct the EMP right into your appliance.

What if the electrical appliance is running?

Mmm, I wouldn’t expect that to make much of a difference.

Hey, in Jericho that lady’s Rolex died from the EMP. Would that really happen?

Most cheaper watches are electronic, and keep time by measuring the piezoelectric oscillation frequency of a little chip of quartz. EMP is likely to zap those kinds of watches. But a Rolex? Those are normally mechanical rather than electronic. The EMP shouldn’t do anything to them.

Would my car still work?

Depends on how old it is. Your fancy-schmancy CPU-controlled electronic fuel injectors are likely to die, as are any other electronics in your car. Older cars are more likely to be okay, since their electrical systems are mostly just wires, like the starter.

Can you fix stuff that an EMP has damaged?

For the most part, no. Well, let me back-pedal some: you can’t fix the individual components, but you might be able to fix the whole device by swapping out undamaged parts. Semiconductors such as transistors and diodes fail by melting internally and causing a short, and there ain’t no fixing that. Capacitors will fail when the EMP-induced voltage is more than the capacitors’ dielectric breakdown threshold, and then they’re useless. If plain vanilla wires are damaged, it’ll be from them shorting through their insulation and into neighboring wires. That’ll mostly happen when the wires are coiled up, like in transformers. Replace the insulation (or, heck, the entire wire) and you should be okay.

Come on, can’t you just tell us what will survive and what will fry?

Not easily. It depends on too many variables. How strong was the bomb? How high was the detonation? Is the equipment inside a building that has a lot of metal in it, which will shield stuff that’s inside? Is the equipment near an unshielded power line?

I can tell you what’ll be zapped first. Semiconductors are the most susceptible, especially low-power transistors. Capacitors are next, then film resistors, then wire-wrapped resistors, then wire-coil devices like transformers and inductors and car starters. So anything computerized or that has a circuit board in it is most susceptible, but your old-fashioned toaster is probably okay.

But if the EMP is strong enough, everything’s going to go. Fuses will blow, circuit breakers will trip, wires will arc, and everyone is out of luck.

3 thoughts on “EMP Q and A

  1. Engineering. And it’s those engineers that build weapons of mass destruction and my orbital death lasers and the like, not physicists.

    I need to shower now. Thanks! 😉

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