‘Passive’ refers to the fact that this type of filter is incapable of power gain and uses no active components. This also means that no external power source is needed for it to function.
A low-pass filter, as the name suggests, allows low frequencies to pass whilst cutting off higher frequencies. The cut-off frequency (Fc), is calculated by using the formula below. ‘R’ is the resistor value, and ‘C’ is the capacitor value.