V- in Part II: How to Find it?

[Janiceleong26]

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]

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

 

[gleem]

But V_out and V_R are given.

 

[Janiceleong26]

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]

There is no zero in my equation in post #2

 

[Janiceleong26]

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]

That is the general definition of gain.

 

[Janiceleong26]

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

 

[gleem]

Why do you want V^- ?

 

[Janiceleong26]

Why do you want V^- ?

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

 

[gleem]

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]

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]

[ Mentor note: this thread has been tidied up ]

 

[Janiceleong26]

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.

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