Find Vout for Op-Amp Circuit with Attached Image

[Metamorphose]

1. Please refer to attached image.



2. The attempt at a solution.

I noted that V_b was grounded and would therefore be equal to 0 and because one of the two op-amp rules states that V_a = V_b, both will be equal to 0.

I wrote an equation at node V_a:

[V_a - V_in]/R₁ + [V_a - V_out]/R₂ = 0

Because V_a is 0, the equation simply became:

-V_in/R₁ - V_out/R₂ = 0

And plugging in the given values for part (a), I acquired - 5V. I'm not sure if this is correct or not as the book does not have a solution manual available yet.

 

[lewando]

-5V is right. In this configuration, the circuit is an "inverter".

 

[Metamorphose]

Thanks! I was just wondering :)

 

[CWatters]

Just for completeness...

Take your equation...

-Vin/R1 - Vout/R2 = 0

then rearrange it to give..

Vout/Vin = -R2/R1

where Vout/Vin is known as the Gain.

a) R2 = R1 so Gain = -1
b) etc