School me. Capacitive Reactance.

[Kipper4]

Thanks for the guidance Paul it's appreciated.

I'll look into plots too.

[amptramp]

I always visualized impedance as having a resistance that goes left to right and a capacitance that goes down and an inductance that goes up.  The hypotenuse is the magnitude of the combined impedance.

[tubegeek]

If you want to geek up the math on this completely, here is a great resource. This will help you get into the necessary translation between angular functions (trigonometric sine wave behavior) and right-angle, Pythagorean vector space - which as the poster above observed, is exactly what is going on here. This is because the imaginary axis is at right angles to the real axis and Euler's identity offers a very practical method for converting between the two seemingly separate (but actually, exactly equivalent) worlds that is amazingly powerful. Every trig identity you struggled with in precalculus becomes a matter of a few minutes' work using this approach - it's absolutely some of the best math instruction I've ever seen.

It also happens to be exactly the right topic for fully understanding the behavior of resistors, inductors, and capacitors in the frequency treatment of audio signals. Audio electronics is possibly the best evidence available for the statement that "imaginary numbers aren't."

Visual Complex Analysis by Tristam Needham:

http://www.amazon.com/Visual-Complex-Analysis-Tristan-Needham/dp/0198534469

[DrAlx]

Kipper, ignore all the maths on this wikipedia page...

https://en.m.wikipedia.org/wiki/Bode_plot

All you need are the two pictures near the top showing magnitude for high-pass and low-pass filters. Those plots are for simple filters that consist of a voltage divider with one R and one C.  Look at the brown line marked with little triangles.Here is all you need to know...

1) The plots show the ratio of output power vs input power, measured in dB.
2)  0 dB means all the power gets through. That is the horizontal section in the graph.
3)  Minus 3 dB means 1/2 of the power gets through. That corresponds to the location of the bend in the curve.
4) Beyond the bend in the curve, less and less power gets through. That is the sloping section.

All you really need to worry about in most cases is the location of that bend, since it fully characterises the whole graph.  In simple terms you can think of that "minus 3 dB" point as marking the boundary between the frequencies that get through and those that get killed off.

The frequency where the 3 dB loss occurs for a simple RC filter is given by

f = 1 / ( 2 * π * R * C )

So most of the time you do not try and pick a frequency of interest and plug in resistance and reactance values. That is tedious as Paul pointed out, and even if you managed to get the correct answer you would only know about that one frequency. No, it is much more sensible to work out the location of the -3dB point ( I.e. the frequency where half the signal gets through) since then you know what happens to ALL frequencies.

[Kipper4]

Thanks guys
Im getting there.

[Fast Pistoleros]

I always visualized impedance as having a resistance that goes left to right and a capacitance that goes down and an inductance that goes up.  The hypotenuse is the magnitude of the combined impedance.

ELI the ICE man