How to Determine V- Without Knowing Resistance?

Janiceleong26 · Mar 28, 2016

1. Homework Statement

For part ii) ,
V₊ is 69mV, but how to determine V_-? We don't know the resistance of X, so we can't find the p.d. across X, so how to find V_-?

Homework Equations

V_out =A₀(V₊-V_-)

gleem · Mar 28, 2016

Isn't the gain of this amp V_out/V_R?

gleem · Mar 28, 2016

But V_out and V_R are given.

Janiceleong26 · Mar 31, 2016

I'm sorry, but can you please explain to me why is V^-=0 in your eqn for the gain in post #2 , thanks

gleem · Mar 31, 2016

There is no zero in my equation in post #2

Janiceleong26 · Mar 31, 2016

gleem said:

There is no zero in my equation in post #2

Then, how did you know that the gain is Vout/V_R? Why didn't you take account of V^-?

gleem · Mar 31, 2016

That is the general definition of gain.

Janiceleong26 · Mar 31, 2016

OK.
V_out=A_o(V⁺-V^-), am I right?
V_out=5.8V
V⁺=69mV
V^-= ?

gleem · Mar 31, 2016

Why do you want V^- ?

Janiceleong26 · Mar 31, 2016

gleem said:

Why do you want V^- ?

So that I can use the formula, V_out=A₀(V⁺-V^-) ,and get A₀

gleem · Mar 31, 2016

The question was what is the gain of the circuit not the op-amp. that's why I commented on the simplicity of the question.

LvW · Mar 31, 2016

Janiceleong26 said:

So that I can use the formula, V_out=A₀(V⁺-V^-) ,and get A₀

So you are interested in Ao ?
Up to now I was of the opinion you were looking for the gain of the whole amplifier stage?

NascentOxygen · Mar 31, 2016

[ Mentor note: this thread has been tidied up ]

Janiceleong26 · Mar 31, 2016

gleem said:

The question was what is the gain of the circuit not the op-amp. that's why I commented on the simplicity of the question.

LvW said:

So you are interested in Ao ?
Up to now I was of the opinion you were looking for the gain of the whole amplifier stage?

Ohhh.. I get it now
Sorry I thought they were asking for A₀
Thanks so much