I was not intending to solve the problem, since I am just looking over all problems in the book. Something caught my attention, however. I was looking at node c, the one labeled with \$v_c\$ in the Figure. If I were to apply Kirchhoff's Current Law to then perform node-voltage analysis, I would not know what currents to write down. I know the current flowing into the positive input of the second OpAmp is zero, so that means there is either current going into/coming out of the output of the first OpAmp, and current through the 150K resistor; or else, no current goes through the 150K or out of/into the first OpAmp output. Then, what is the point of cascading two OpAmps?
Yes, current can flow into and/or out off the output of an op-amp.
However, an op-amp provides a voltage output. It is the circuit that surrounds the op-amp that dictates what current will flow into/out of the op-amp's output.
To apply hand analysis to your circuit you would assume:
- \$V_b = 0\$ (due to op-amp action)
- \$V_e = V_c\$ (due to op-amp action)
Apply KCL at the \$V_b\$ and \$V_o\$ nodes.
You now have 2 equations with 2 unknowns (\$V_o\$ and \$V_c\$).