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

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1. Sep 20, 2016

### eroc1002

1. The problem statement, all variables and given/known data
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?

2. Relevant 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.

2. Sep 20, 2016

### kuruman

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.

3. Sep 21, 2016

### rude man

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.

4. Sep 21, 2016

### kuruman

Right you are. I missed that.