 #1
peasngravy
 72
 6
 Homework Statement

FIGURE 1 shows two amplifier circuits, each of which has one unknown
voltage (shown highlighted). Select, from TABLE A, the most
appropriate value for the unknown voltages for each circuit. Assume that
the opamps are ideal and that the magnitude of their output voltages is
less than their maximum peak output voltage swing (VOM).
 Relevant Equations

V+ = V1/(R+10R)
(V2  V)/R = (Vo  V)/10R
Hi  I have made an attempt at both of these circuits, but I am not 100% sure I am correct. Would it be possible to check if I have this right, and if not, please give me some pointers as to where I have gone wrong? Thanks
First opamp
Given data:
Vo = 5V
I have called the voltage feeding into the noninverting input V1 = 0.5V
voltage feeding into the inverting input = V2
For non inverting input V+ = V1/(1+10)
For inverting input V :
(V2  V)/R= (Vo  V)/10R
V2  V =(Vo + V)/10
10(V2  V)V = Vo
10V2  11V = Vo
Plug in values
(10*0.5)  11V = 5
11V = 10
V =10/11 = 0.909V
As it is an ideal opamp:
V+ = V = 0.909V
Therefore:
V+ =V1/(10+1)
V1 = V+ * 11
V1 = 0.909*11 = 10V
Second opamp
At noninverting input:
V+ =Vo/(R+R)
V+=12/2=6V
As it is an ideal opamp:
V+ = V =6V
Due to short from inverting input to output, output voltage (V) is 6V