There are plenty of references tothis claim on the internet that tying knots in power cables willprevent a piece of equipment e.g. television or computer from apower surge.
How can this be debunked (or proven) using mathematics?
I stumbled across this which seems reasonable to me, but isthere some way this can be proved?
The surge impedance of any line is the square root of itsinductance divided by its capacitance, and electromagnetic wavestravel most readily down a line where that surge impedance doesn'tchange. A point of changing impedance is a discontinuity thatcauses a partial reflection of the wave back towards its source. Asan example, the end of the line is a surge impedance jump toinfinity and the whole wave is reflected back (which means the wavevoltage at the open end doubles!) This is also the reason why youwant to use terminators on the ends of coaxial cables. Open-endedcables will reflect back the signal causing poorer picture qualityand ghosting (and similar things happen for poorly made connectionsthat have higher impedances than the surge impedance of thecoax).
Knotting the line gives that part of it a higher inductance(think of the knot as a coil with a couple of turns). That meanstwo surge impedance discontinuities (from line to knot, and fromknot back to line). It seems to me (too lazy to resort to doing themath) that this is bound to reduce the magnitude (voltage andcurrent) of a surge passing through the knot because some will bereflected back. However, I'd guess that the reduction would besmall.
