The circuit above is a low-pass filter while the one below is a high-pass filter. Both cut-off frequencies are at 1KHz.
In the low-pass filter (above), the source frequency is at 1.5KHz, and only frequencies below 1KHz are allowed to pass, the source frequency is attenuated.
In the low-pass filter (below), the source frequency is at 0.5KHz, and only frequencies above 1KHz are allowed to pass, the source frequency is attenuated.
