How does a filter work? How does it filter?

From electrical engineering, all components can be summarized into three basic categories, namely resistance, inductance and capacitance. The resistance of a resistor is independent of the frequency of the alternating current. The resistance of an inductor (called inductive reactance) Xl=2πfL, which is proportional to the frequency of the alternating current. The higher the frequency, the higher the inductive resistance. A capacitive element is the opposite of an inductive element, its reactance Xc=1/2πfC, which is inversely proportional to the frequency of the alternating current.

So, in electrical engineering, often use the LC component of different frequencies of the AC power reactance is different, the AC power shunt, known as filtering.

According to different functions, filters are usually divided into three categories: low-pass, high-pass, band-pass. They have a wide range of applications in electrical and electronic circuits. The simplest and most typical example is our common DC regulated power supply, rectifier circuit behind the access to the capacitor, is to reduce AC pulsations and set. It is a low-pass filter.