This video shows how frequency-domain concepts can be used to find the output signal of an ideal-low pass filter (LPF).

The input to the LPF is a periodic pulse train signal. We use the Fourier series representation of the input signal to determine which frequency components pass through the LPF to easily write a time-domain expression for the output signal y(t).

This video shows how frequency-domain concepts can be used to find the output signal of an RC circuit.

The input to the RC circuit is a fully-rectified sinusoid signal. We use the frequency-domain representation of this signal from a previous video example to determine the output signal y(t). The key concept here is that each frequency component passes through the RC circuit unchanged except for being multiplied by a single complex number.

The complex number that multiplies each frequency components is given by the transfer function of the system evaluated at the point j*n*omega_0.