How are the capacitors and inductors of a low-pass filter Pi-network arranged between the network's input and output?
Why A Pi-network is named for the shape of the Greek letter pi: two vertical legs to ground with a horizontal element bridging them. For a low-pass version, the shunt legs must be capacitors (low reactance to high frequencies, shorting them to ground) and the series element must be an inductor (high reactance to high frequencies, blocking them from reaching the output). Low frequencies pass straight through the coil while the capacitors look like open circuits, so the network passes the low end and attenuates the high end. This is the classic tube amplifier output tank arrangement used for both harmonic suppression and impedance matching.
Watch out Two inductors in series with a capacitor to ground is also a low-pass filter, but it forms a T-network, not a Pi; the two series capacitors with a shunt inductor is a high-pass T.
Pi = two legs down, one bar across. Low-pass Pi: caps are the legs to ground, coil is the bar.