Art of Electronics Exercise 4.3 Operational inverter

[CSOleson]

Homework Statement

The circuits in Figure 4.14 let you invert or amplify without inversion, by flipping a switch. The voltage gain is either +1 or -1, depending on the switch position.
http://tinypic.com/r/2hnql2c/6
http://tinypic.com/r/2hnql2c/6

Homework Equations

Gain for the first image with the switch set to ground is equal to -R2/R1, because it is an inverting amplifier, struggling to identify how to consider the circuit as a follower, because it doesn't look like a typical follower circuit. Unsure how to consider the circuit when the positive and negative terminals are connected.

The Attempt at a Solution

 

[berkeman]

Homework Statement

The circuits in Figure 4.14 let you invert or amplify without inversion, by flipping a switch. The voltage gain is either +1 or -1, depending on the switch position.
http://tinypic.com/r/2hnql2c/6
http://tinypic.com/r/2hnql2c/6

Homework Equations

Gain for the first image with the switch set to ground is equal to -R2/R1, because it is an inverting amplifier, struggling to identify how to consider the circuit as a follower, because it doesn't look like a typical follower circuit. Unsure how to consider the circuit when the positive and negative terminals are connected.

The Attempt at a Solution

What is the difference in voltage between the + and - inputs for an opamp in the follower configuration? So what is the feedback current in this configuration?

 

[CSOleson]

are the + and - inputs equal, because of the negative feedback loop?

 

[CSOleson]

so the voltage across the 1st resistor would be 0V because it is V+ - V-

 

[berkeman]

are the + and - inputs equal, because of the negative feedback loop?

so the voltage across the 1st resistor would be 0V because it is V+ - V-

Correct-a-mundo

Kind of a weird follower, but that's one of the ways that H&H teaches us how to be comfortable thinking about circuits. Have you seen this thread?

https://www.physicsforums.com/newreply.php?do=newreply&p=4315656