The coil opposes
the flow of ac current, as a resistor does in a dc circuit.
This opposition
is called inductive reactance, XL.
The bottom formula shows how inductive reactance is calculated. f is the frequency of the applied voltage, and L is the value of the coil in Henries. It can be seen
from this formula that the value of XL
goes up as the frequency
This means that
as the value of L or f increases, the opposition to the flow of ac
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