I think I understand now, I need to think of 'Reactance' as more of a control of a component rather than resistance even though they sort of mean the same thing, this is just a miniscule amount in real terms hence measuring on graphs so it enables to see what we are on about & set the required frequency
Resistance and reactance BOTH are that quality of a component that
lowers the charge flow (current) in a circuit.
One
resistor, all by its lonesome (at a constant temperature) will resist current very predictably and
always the same way, whether it is an AC or DC current. The resistance is totally predictable (and "linear": a straight line, no curves) based on its resistive value ONLY. A 1k resistor will provide the same current
reduction in a circuit for DC or for AC (regardless of the frequency). Always.
If you were to put another resistor in series (or parallel) with the above resistor, its resistive function in this new circuit would be, once again,
the same, linear and utterly predictable, no matter the signal type nor frequency.
In the case of a capacitor (say, 1uf), however, the amount of its resistance to current is NOT always the same. In particular, it varies considerably with a variation in the frequency of the signal being applied to it.
And if you add another component (in series or parallel), such as a resistor or an inductor, that component will radically alter how the capacitor "reacts" to current. It is predictable, but NOT linear.
So now I moved my understanding towards the phase (which is the start of the cycle (Hz) but am I now right in thinking that the reactance is the ability to control the time of the complete cycle by using different value caps giving us required frequency
Two issues here. 1. Yes, the phase value is the start of the cycle, generally in relation to zero degrees (up to the 360° in one complete cycle). And 2. by controlling the timing (which is to say, frequency) with capacitors (and other components as well) one can alter the frequency of the signal.
Just had another look at LOG graph, so what your showing me is the fact that the lower the V the higher the frequency, the higher the V the lower the frequency,
Well, if you're looking at the graph from right to left, then, yes. But keep in mind that the V is nothing more than a representation of the amount of signal getting
through the cap. As the frequency goes up, eventually NONE of the signal gets through.
it is simply a graph showing what gain (V) (or my words-charge) you would have at a set frequency in the cap over one Hz
This part is correct. But, please see the last sentence in this post.
I think you may be confusing the term
Cycle with
Hz. One cycle is one cycle, that all. Hz is the number of repetitive cycles over a given period of time (generally one second), i.e., frequency.
So that would make KISS's example of -3db always 707m the charge capacity at a given frequency, does that make Xc a simple way of finding a charge rate for cap over one Hz, then somehow it is going to have to be tied in with the phase - start time of the cycle
You've mixed and matched several differing concepts here.
1. dB. A method of considering the "gain" (think volume) of a circuit. It can be positive (+ going up) or negative (- going down) but ALWAYS relative to the initial input level. It is a value that is a
result of a circuit. It is not something that affects the circuit (it's an output, not an input).
2. Xc is something that has to derived. That is, whereas a resistor has clearly stated on it what its resistance is, a capacitor NEVER has its reactance stated because its reactance varies all over the place depending on many differing situations.
3. And neither of these is affected by phase. We should probably skip a more thorough discussion of phase fro a later time. It's important, but not all that relevant at the moment.
This would mean you cannot choose any old R as it affects the frequency, it is part of the circuit in a bigger way than I ever imagined, they actually a crucial role to play, so if the cap is the cycle monitor, R must be the control room setting
(My
emphasis).
Yes to the first part. I'm not sure of your analogy in the underlined part.
Maybe it would help to realize that the SA (Signal Analyzer) example graphs only show a voltage level (you could almost think of it a DC level) as a sinewave of
increasing frequency is presented to the RC circuit. Granted, the graph looks like a wave, but it isn't really a wave.
It's just showing us how much of the sinewave, at any given frequency, that is going
into the RC circuit is
getting through it to the output of the circuit.
it is all part of the learning process
