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### Why does high capacitance correspond to low impedance and vice versa? Physically, why do capacitors increase in impedance when you lower frequency, and vice versa?

Capacitive impedance is , which means that, for a given AC frequency , a large capacitance means a smaller impedance (i.e., more current for a given voltage according to the AC Ohm's Law, ). Here's the qualitative explanation: if you have a very large capacitance, that means a lot of charge can be stored for a given potential difference, and the capacitor takes a long time to charge up. In an AC circuit, current only passes through a capacitor during the time a capacitor is either charging or discharging. If a capacitor is fully charged or discharged, it acts like an open circuit and does not pass current-- its impedance is infinite. A large capacitance means that (for a given of AC driving voltage) the capacitor will spend more of its time in a charging or discharging mode. A small capacitance means that the capacitor will charge up quickly and spend most of the cycle behaving like an open circuit and so not passing current.

Similarly, for a given , a fast driving wiggle will mean that the capacitor is constantly charging-discharging-charging-..., and so passes more current on average (so has low impedance). In contrast, a small will mean that the capacitor has a chance to charge all the way up or discharge all the way down, and so will be open-circuit-esque during much of the cycle, and hence won't pass much current (so has high impedance).

Both the size of and matter; impedance is related to the product of them.

Next: Can you clarify reactance? Up: Content Questions Previous: How did you go
Kate Scholberg 2017-02-05
LOW impedance capacitors