Question

An ideal square wave with period of 20 ms shown in the figure, is passed through an ideal low pass filter with cut-off frequency of 120 Hz. Which of the following is an accurate description of the output?

Answer 1

Given, T = 20 msec
Fundamental frequency,
$f_0=\frac{1000}{20}=50Hz$
The given signal is an odd signal and it also has half wave symmetry. So, it will have spectra components only for odd harmonics. So, the spectrum of the signal will have component of 50 Hz, 150 Hz, 250 Hz, 350 Hz, ....
When passed through an LPF of cut-off frequency 120 Hz, the output of filter has only 50 Hz component. So, option (c) is correct.