Help with Ideal Operational Amp?

Question

https://eee.uci.edu/toolbox/quiz/form/get_image.php?image_id=83496&hash=DIrS7a9QcS

1) Which is true:
No current flows through the 3 Ohm resistor.
No current flows through the 2 Ohm resistor.
Vout is infinite
(V+) - (V-) = 2Volts

https://eee.uci.edu/toolbox/quiz/form/get_image.php?image_id=83497&hash=xim797reC2

Which is true for the second link

2) No current flows through the 2 Ohm resistor
No current flows through the 3 Ohm resistor
Current flowing through 3 Ohm resistor is equal to the current flowing through the 2V source.
No current flows through the 2 Volts source

3) For the circuit of Problem 2, the output voltage V_out is equal to
10 Volts
10/3 Volts
3 Volts
None of the above

Answer 1

1) No current flows through the 2 Ohm resistor.



This is one of the golden rules for ideal op-amps. The inputs draw no current.



2) No current flows through the 2 Volts source



This is again, one of the golden rules for ideal op-amps. The inputs draw no current.



3) 10/3 Volts



The op-amp configuration is identified as a Non-inverting amplifier. Its input->output relationship is a commonly known derived formula:

Vout = Vin *(1 + Rfeedback/Rground)



Plug in Vin=2 V; Rfeedback=2 ohms; Rground = 3 ohms;



and get your answer

Answer 2

For the second link:-

2) Current flowing through the 3 ohm resistor is equal to the current.......

REASON: Now for an ideal op-amp the difference voltage (Vid) (between the +ve and the -ve terminal) should be zero. hence the voltage drop across 3 ohm resistor has to be 2V.



3) The config is that of a non-inverting op-amp. So the formula for the Vout is (1+ Rf/R1)*Vin. So using this formula the answer comes out to be 10/3 Volts.



For the first link:-

Sorry cant help you with this answer much. It is obvious that for an ideal op-amp the voltage gain is infinite and so the output voltage must be infinite but that is for the open loop op-amp and this is a negative feedback op-amp. I am not convinced with any of the options. But do inform me if you get the correct answer.



All The Best.

Answer 3

It's obviously a homework question, so I'm not going to give you the answer. The first thing across the voltage source is 2:1 attenuator, at the output (junction) of which there will be 1/3 of Vin. What follows is a conventional inverting amplifier. I'm sure you know how to calculate its gain. The polarity indicators at the source and output serve no useful purpose. What is more, one of them must be wrong (since it's an inverting amplifier).