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Opposite in nature to a high-pass filter, a low-pass filter is a filter that allows signals with a frequency lower than the cut-off frequency (the frequency at which the output voltage is 70.7% of the source voltage) to pass through it. It also attenuates those signals whose frequency is higher than the cut-off frequency. In other words, low-pass filters help in removing short-term fluctuations, and provide a smoother form of signal.
In electronics, a low-pass filter is basically implemented in two ways: inductive low-pass filter and capacitive low-pass filter. The difference between the two lies in the way the components are arranged. In inductive low-pass filters, the inductors are inserted in series with the load, whereas in capacitive low-pass filters, the resistors are inserted in series and a capacitor is inserted in parallel to the load.
Many applications make use of low-pass filters as they are known to filter noise from a circuit. In power supply circuits, they are used to remove AC ripples. In order to block harmonic emissions that could potentially cause interference, radio transmitters make use of low-pass filters. They are also used as inputs in audio applications and certain loudspeakers in order to prevent the high pitches that are not produced efficiently. Low-pass filters are also used as integrators in electronic circuits.