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Input resistance for AC input

Q

qwerty

Jan 1, 1970
0
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?
 
D

Don Kelly

Jan 1, 1970
0
Govind said:
Yes. Its wrong. Input resistance of an ideal voltage source is Zero.
pls click the following link for more iformation
http://en.wikipedia.org/wiki/Voltage_source
--------------------
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 [email protected]
remove the X to answer
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