Input resistance for AC input

I read on a book that when a circuit has an AC voltage source as
the input then it's input resistance is
Ri= ui/ii
where ui is the instantaneous input voltage and ii the
instantaneous input current.
Isn't this false?
Reply to
qwerty
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It's not a definition that I've seen. It doesn't strike me as a good definition in general because the math would get a little dicey at the zero crossings. Otherwise I guess it would be basically correct for a resistive network, even if resistances changed with time.
Reply to
operator jay
Yes. Its wrong. Input resistance of an ideal voltage source is Zero. pls click the following link for more iformation
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Reply to
Govind
-------------------- The input resistance implied is not that of the source but that of the circuit supplied by the load-as seen by the source and is independent of the source.
In any case, an ideal voltage source is a convenient fiction useful in circuit analysis but hard to find in the real world (sure with fast enough feedback one can come close).
As for the definition- it simply notes that v(t)=R*i(t) rather than v(t)=L*(di/dt) or i(t)=C*(dv(t)/dt That is correct.
If R is constant over the range of possible v(t), i(t) then be happy, Ohm's Law is valid and life is simple(?) .--
Don Kelly snipped-for-privacy@shawcross.ca remove the X to answer ----------------------------
Reply to
Don Kelly

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