Electromagnetic pulse?

Question

what can cause it and how long canit last

Answer 1

A spark can cause an electromagnetic pulse (EMP). It won't be very strong but it is still an EMP. Typically, EMP is caused by the sudden transmission of current between two electrodes. Lightening has an EMP associated with it. A nuclear weapon detonated in the atmopshere creates EMP by ionizing the atmosphere, causing the free electrons to move. The key to making EMP is a sudden change in current between two electrodes. If therei s a steady current, then ethere will not be any EMP.

EMP doesn't last long. Usually it lasts as long as the sudden jump lasts. If the current becomes a steady state current - doesn't change in time - then there is no EMP. EMP from a nuclear weapon lasts a bit longer - it depends on how long it takes the ionized atmosphere to recombine.