Page 1118 - Basic Electrical Engineering

connected to the ground. The input voltage is V and the output voltage is
in
V . The voltage at point Q is υ.
0
Current i through the resistance R is
1
1

As the input impedance of the op-amp is infinite, the whole of i will pass
1
through R . The op-amp having infinite input impedance will not allow any
f
current to flow through it.
Therefore,

As the open-loop gain, A of the amplifier is infinite, and the output
voltage, V is finite, we have
0

If A tends to infinity,
v will tend to zero.
Thus, the potential of point Q can be considered equal to zero. This is also

referred to as a virtual ground potential. With v = 0, from equation (i),

or,