# op-amp circuit explanation [closed]

Hi everyone I'm studying Op-Amp but I can't understand this point in the AC circuit :

In the first picture it says Vo = Ic * Rc, and in the second picture I have the value of Ic, when I try to apply this in the given formula before the answer is wrong. Why?

This second formula is used instead of the first one?

Is there is a difference ?

You're first picture has no component called $R_c$, but we can clearly see that $V_o = I_c R_c$ does not apply for the second picture, but instead it is $$V_{R_c} = I_c R_c \qquad V_o = V_{cc} - I_c R_c$$
But when doing a AC-Analysis $V_{cc}$ is removed, as it is a constant voltage source, and therefor $R_c$ is short-circuited to ground. Then you actually have $V_o = I_c R_c$.