# capacitive coupling question

Discussion in 'General Electronics Chat' started by holden c, Mar 1, 2014.

1. ### holden c Thread Starter New Member

Jan 23, 2014
19
2
i read in a book that the higher the resistance, the more parasitic capacitive coupling we have on the wires that connected to that resistor. Can anyone help me out to understand this? why this is so? I mean, is this thing true at all?
thanks

2. ### BillB3857 Senior Member

Feb 28, 2009
2,402
348
If you compare the capacitive reactance of the distributed capacitance with the value of the resistance, you can see that as the resistance increases, the distributed capacitive reactance has a greater effect.

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3. ### #12 Expert

Nov 30, 2010
16,705
7,355
The important word is, "coupling", as in "amount of current induced into the circuit". I am going to call it, "noise" because it is being coupled by stray (unintended or parasitic) capacitance.

For any physical circuit, stray capacitance happens. For any fixed physical circuit, that capacitance is stable and has an Xc which changes with frequency. Any radiated energy in the neighborhood is coupled into the circuit at V/Xc (which equals V2PiFC). The resulting, "noise" is introduced into a voltage divider with Xc as the supply impedance and R as the drain resistance. The higher the resistance of the circuit, the less radiated noise will be drained to ground.

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