# How to graph amplitude vs. frequency for a Low-Pass Filter?

## Homework Statement

For my lab class my professor wants us to graph the theoretical amplitude of the output from a low-pass filter vs. frequency. I have the resistance and capacitance that I chose for the RC circuit and a V(in). Is there an equation that I should be able to use to relate these and produce a graph?

## Homework Equations

In my notes I have an equation Vout = Vin*(Rc/sqrt(R^2 + Rc^2) and Rc = 2πfε but I have no idea what epsilon represents because I forgot to ask my professor when I was taking the notes.

3. Attempt at a solution

After doing some research, I tried to use 1/sqrt(1+(2πfRC)^2)to get a ratio of Vo/Vin but all I got was a straight line.

kuruman
Homework Helper
Gold Member
I think the epsilon should be C and RC is the capacitive reactance 2πfC.

As to why you got a straight line, it probably has to do with not plotting in the correct frequency range.

rude man
Homework Helper
Gold Member
In my notes I have an equation Vout = Vin*(Rc/sqrt(R^2 + Rc^2) and Rc = 2πfε
First, don't use "Rc" for capacitive reactance. Use Xc. "R" is always resistance in this context.
Second, capacitive reactance is not 2πfC. It's the inverse.

kuruman