Hacker Newsnew | past | comments | ask | show | jobs | submitlogin

I always understood that CMEs cause EMPs, so that's what I was talking about.


It looks like nitrogen (the user, not the gas) has saved me the trouble of doing the math, but he (she?) has omitted an explanation of the physics so I'll leave one here. Sorry if you already know it, but if you already know it and didn't apply it that's your own damn fault :P

Google keyword: Faraday's Law of Induction

Kirchoff's Voltage Law (sum of voltages around a loop is zero) breaks when there's a changing magnetic field poking through the loop. The amount it breaks by is V=A*dB/dt where V is "extra" voltage, A is area of the loop, and dB/dt is change in magnetic field with time.

An EMP creates a shockwave of enormous dB/dt. Even loops with small A can induct enough voltage to fry sensitive electronics.

A CME has dB/dT of 5mT/min (linked article). Fridge magnets are ~5mT (wikipedia) so you could make a local field with similar dB/dt by walking very slowly towards your computer while carrying a fridge magnet. Of course, unlike fridge magnet vs computer, CMEs are damaging because A is massive (distribution infrastructure is a big loop) so even though dB/dt is tiny they can fry power lines.

That is, unless real-time distribution management notices voltages starting to go haywire and shuts them down because a CME isn't instantaneous and hard to anticipate like an EMP. Or circuit breakers do their job because voltage / km is relatively small. Or inductive loads (anything with a motor or transformer in the circuit) protect themselves from what essentially looks like just another voltage spike (they happen all the time because every time you shut off a poorly designed inductive load it kicks a high voltage back onto the line). Or TVS diodes do the same for sensitive electronics somehow connected without a transformer...

tl;dr a CME is not like an EMP. Same physics equation but with very different numbers.




Guidelines | FAQ | Lists | API | Security | Legal | Apply to YC | Contact

Search: