Closed Loop Concepts and Simplifications – Op Amp

Substituting a = ∞ (1) into (16) results in,
[pmath]A  = 1- 1/b = R2/R1[/pmath]
Recall that in equation (6) we state that Vd, the voltage difference between Vn and Vp, is equal to zero and therefore, Vn = Vp. Still they are not shorted together. Rather there is said to be a virtual short between Vn and Vp. The concept of the virtual short further simplifies analysis of the non-inverting op amp circuit in Non Inverting Amplifier.
Using the virtual short concept, we can say that,
[pmath]Vn = Vp = 0  [/pmath]
In this configuration, the inverting input is a virtual ground.
We can write the node equation at the inverting input as

We can write the node equation at the inverting input as

[pmath](Vn – V i) /R1 + (Vn – Vo) /R2 = 0[/pmath]

Since Vn = 0, rearranging, and solving for A we get

[pmath]A = 1 – 1/b= – R2/R1[/pmath]
The same result is derived above. Using the virtual short concept reduced solving the non-inverting amplifier, shown in Non Inverting Amplifier, to solving a resistor divider network.