Here are three circuits which are identical except for the frequency of the source. Capacitors are able to "pass" higher frequencies more easily than lower ones. The higher frequency of the bottom circuit results in a higher current. This is because the voltage across a capacitor is proportional to the charge stored in it, and charge is the accumulation of current over time. With a shorter A/C cycle, a higher current can flow for a shorter period of time and still result in the same peak charge (and thus the same peak voltage).
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