RL filter on the scope

// A generator into an RL low pass, both ends on the scope.
//
// L = 160 mH, R = 1 k. The corner is where the inductor's reactance equals
// the resistance:
//
//   f0 = R / (2 pi L) = 1000 / (2 pi x 0.16) = 995 Hz
//
// The generator is set to 1 kHz, as good as on the corner, so the filtered
// trace (blue, CH2) comes out at
//
//   |H| = 1 / sqrt(1 + (2 pi f L / R)^2) = 0.705
//
// of the yellow one, and an eighth of a cycle behind it. Count the divisions:
// 2 V/div vertically, 400 us/div across.
//
// Things to try. Take the frequency to 100 Hz and the two traces sit on top
// of each other; take it to 10 kHz and the blue one is down by ten. Swap the
// resistor and the inductor and it is a high pass. Halve L and the corner
// doubles: an inductor's reactance grows with frequency, which is the whole
// difference from the capacitor in the RC example, whose reactance shrinks.