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Poster has been reminded to post schoolwork in the Homework Help forums (moved from EE)

Hi everybody!

This is my first post as I am needing some help in a question I am struggling with. Not looking for answers, just some guidance in the right direction.

[/B]

I need to calculate the unknown, highlighted, voltages on the op amp circuits (attached).

Assume all op-amps are ideal

See below

I have done the following so far:

a) Inverting

A=-Rf/Ri =(-100)/10=-10

Vi =I1*R1 =0.00001*100000=1 V

Vo=(-Rf/Ri )*Vi

Vo =1*-10

Vo =-10 V

b) Summing

Vo=-(Rf/R_1 V_1+Rf/R_2 V_2 )

-2=(Rf/R_1 1+Rf/(R/2) V_2 )

c) Non-inverting

V1 =V2

V1 =100 mV

V2 =100 mV

d) Current to Voltage

Vo=-I1*Rf

Vo =-0.0002*10000=-2

Vo =-2 V

I am struggling the (b). I can't see how to calculate given only one value, and also with (c)

Many thanks in advance, happy to discuss the methods.

Joel

This is my first post as I am needing some help in a question I am struggling with. Not looking for answers, just some guidance in the right direction.

## Homework Statement

[/B]

I need to calculate the unknown, highlighted, voltages on the op amp circuits (attached).

Assume all op-amps are ideal

## Homework Equations

See below

## The Attempt at a Solution

I have done the following so far:

a) Inverting

A=-Rf/Ri =(-100)/10=-10

Vi =I1*R1 =0.00001*100000=1 V

Vo=(-Rf/Ri )*Vi

Vo =1*-10

Vo =-10 V

b) Summing

Vo=-(Rf/R_1 V_1+Rf/R_2 V_2 )

-2=(Rf/R_1 1+Rf/(R/2) V_2 )

c) Non-inverting

V1 =V2

V1 =100 mV

V2 =100 mV

d) Current to Voltage

Vo=-I1*Rf

Vo =-0.0002*10000=-2

Vo =-2 V

I am struggling the (b). I can't see how to calculate given only one value, and also with (c)

Many thanks in advance, happy to discuss the methods.

Joel

#### Attachments

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