Here, Ip (the current through Rp) is needed.

1) This problem should be done by superposition (when V1=0 and then when V2=0) or it is also possible without that?
2) When V1=0 is the current through R1 and R2 the same (but in opposite directions) or not?

 

Hello,

Do you know how to use superposition with two constant voltage sources?

For this circuit you end up with two different common op amp circuits, one for each source, then add the results.
You can then think about question 2.

Since no values are given you'll have to solve this symbolically.

 

Here, Ip (the current through Rp) is needed.
1) This problem should be done by superposition (when V1=0 and then when V2=0) or it is also possible without that?

This problem CAN be done using superposition, but as to whether it SHOULD be done, that's largely personal preference. Any of the standard analysis techniques will work.

2) When V1=0 is the current through R1 and R2 the same (but in opposite directions) or not?

Apply KCL at the node containing the inverting input of the opamp. What does that tell you about the currents in R1 and R2, regardless of what V1 is?

 

One of the very basic properties of ideal op amps is: current never enters the op amp input. This means that current in R1 and R2 is the same.

 

One of the very basic properties of ideal op amps is: current never enters the op amp input. This means that current in R1 and R2 is the same.

Hi,

That's a good point, but i think we should be careful about using the word, "never".
We often disregard the input bias current and thus simplify by stating that the current does not enter the op amp input, however that is ONLY when the op amp is operating in the linear mode. That is, it has proper feedback to keep it working in the linear region (not saturated for example and in some cases steady state output).

 

Hi,

That's a good point, but i think we should be careful about using the word, "never".
We often disregard the input bias current and thus simplify by stating that the current does not enter the op amp input, however that is ONLY when the op amp is operating in the linear mode. That is, it has proper feedback to keep it working in the linear region (not saturated for example and in some cases steady state output).

which part of IDEAL op amp you did not understand?

 

One of the very basic properties of ideal op amps is: current never enters the op amp input. This means that current in R1 and R2 is the same.

which part of IDEAL op amp you did not understand?

Hi,

Well since you asked, the part where you seemed to be assuming that an IDEAL op amp MUST also be always operating in the linear mode, i guess. The 'ideal' attribute is an intrinsic attribute that does not by itself imply any particular operating mode. Therefore an ideal op amp can be running linear or in saturation, same as a non ideal op amp.

One of the more important points is the current through the input resistor. It can change in an unusual way when the op amp is not operating in the linear mode. That puts a different load on the previous circuit.

Sorry if i misunderstood you or something.

 

As with a diode are a transistor, there are a couple of models or an ideal opamp. The first is the purest, of course, and has infinite input impedance, zero output impedance, infinite gain, and no limit on range of operation for either the inputs or the output. The next step up, and which is probably the most commonly used, applies saturation limits either at the supply rails are a fixed voltage (commonly 2 V) inside them. This model is almost always still referred to as an ideal opamp, just as a diode with a fixed forward voltage drop is almost always still called an ideal diode. From there the various parameters are relaxed and, at some point, it is no longer referred to as an "ideal" opamp.

 

Hi,

Yes and in one model we might think of infinite input impedance and unlimited output voltage.
That might be able to keep the op amp in the linear mode for any circumstance other than maybe a short across the two inputs, but that case as well as others would probably bring us into those murky waters where we dont really have to go for most op amp circuit theory.

For example, a op amp circuit with a short across inputs, non inverting terminal grounded, a short from input source to inverting input, a short from output to inverting input terminal...is the gain equal to 1 or zero
These kind of questions are more for fun than the practical i think, except maybe to talk about theory.