<P> Another way to understand this circuit is through the concept of reactance at a particular frequency: </P> <Ul> <Li> Since direct current (DC) cannot flow through the capacitor, DC input must flow out the path marked V o u t (\ displaystyle \ scriptstyle V_ (\ mathrm (out))) (analogous to removing the capacitor). </Li> <Li> Since alternating current (AC) flows very well through the capacitor, almost as well as it flows through solid wire, AC input flows out through the capacitor, effectively short circuiting to ground (analogous to replacing the capacitor with just a wire). </Li> </Ul> <Li> Since direct current (DC) cannot flow through the capacitor, DC input must flow out the path marked V o u t (\ displaystyle \ scriptstyle V_ (\ mathrm (out))) (analogous to removing the capacitor). </Li> <Li> Since alternating current (AC) flows very well through the capacitor, almost as well as it flows through solid wire, AC input flows out through the capacitor, effectively short circuiting to ground (analogous to replacing the capacitor with just a wire). </Li>

The magnitude response of first order low-pass rc filter is given by