# amplitude in an AC circuit

#### paul_alan

Joined Nov 5, 2011
43
if you have an AC circuit with say, two resistors, and two capacitors connected to a signal generator putting out 15khz and an amplitude of 6V. if the frequency was to be increased or decreased, what effect would it have on the amplitude of a node between a cap and a resistor? would the amplitude decrease with an increase of frequency because the capacitors opposition to current flow decreases?

#### praondevou

Joined Jul 9, 2011
2,942
if you have an AC circuit with say, two resistors, and two capacitors connected to a signal generator
Connected How? Post a circuit please.

Consider simply the impedance of a capacitor changing with frequency. Your circuit becomes a simple resistor/impedance network.

Impedance of a capacitor decreases when frequency increases.

#### paul_alan

Joined Nov 5, 2011
43
i'm looking at node 5 which is the furthest to the right above the 10k resistor and the 0.1 microfarad cap.

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#### praondevou

Joined Jul 9, 2011
2,942
i'm looking at node 5 which is the furthest to the right above the 10k resistor and the 0.1 microfarad cap.
The AC voltage on node 5 (to Gnd) will decrease with lower frequency, because the capacitors impedance increases.

Calculate the impedance of the caps for any given frequency and make a network analysis.

At 15kHz their impedance is a bit more than 100 Ohm, so they are almost negligible.

#### thatoneguy

Joined Feb 19, 2009
6,359
Check out the impedance graph paper in my sigline, there's an example of how to use it in the thread, it should give you some pretty good insight of how frequency and capacitance interact, while resistance is a constant.

Let me know if you have problems.