these two circuits are how filter circuits work. The top filters out high frequency signals and the bottom filters out low frequency signals. This is possible because the impedance of the inductor and capacitor are dependent on the frequency.
Low frequency inductor = short
High frequency capacitor = short
using this is it easier to imagine how this circuit acts as you can see the top circuits output gets larger as the frequency increases. Likewise, the bottom circuit's output grows smaller as the frequency increases.
