# Fourier series / calculate power over resistor

1. Jan 25, 2014

### nikki92

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

V(t) = 4 for 0<t< 1 and 0 for 1<t<3 and repeats itself for all t (negative and positive)

Find the first 5 harmonics of the fourier series in cosine form and find the power if this is the voltage over 100 ohm resistor

3. The attempt at a solution

power = d_dc ^2 / R + .5sum from n=1 to 5 of |v_n|^2 /R = 0.1385 w

This does not seem correct. I am not sure where I went wrong.

Last edited: Jan 25, 2014
2. Jan 25, 2014

### rude man

Where does the sinc come from? Is this some kind of discrete system?

3. Jan 25, 2014

### nikki92

It is a square wave.

Last edited: Jan 25, 2014
4. Jan 25, 2014

### rude man

Why don't you simmply use the integrals for the a_n and b_n coefficients? Then get the series in the form

V(t) = c0 + 2 ∑n=1 to 5 of cn cos(nω1t + øn)?

And what exactly is x_n?