How to Determine V- Without Knowing Resistance?

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AI Thread Summary
The discussion centers on determining the negative voltage (V-) in a circuit where the positive voltage (V+) is known to be 69mV, but the resistance is unknown. Participants clarify that the gain of the amplifier (A0) can be calculated using the formula Vout = A0(V+ - V-), with Vout given as 5.8V. There is some confusion regarding whether the focus is on the gain of the op-amp or the entire amplifier stage. Ultimately, the conversation highlights the importance of understanding the context of the gain being discussed. The thread concludes with participants gaining clarity on the distinction between A0 and the overall circuit gain.
Janiceleong26
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1. Homework Statement
image.jpg


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


Vout =A0(V+-V-)
 
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Isn't the gain of this amp Vout/VR?
 
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Likes CWatters
But Vout and VR are given.
 
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Likes CWatters
I'm sorry, but can you please explain to me why is V-=0 in your eqn for the gain in post #2 , thanks
 
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There is no zero in my equation in post #2
 
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gleem said:
There is no zero in my equation in post #2
Then, how did you know that the gain is Vout/VR? Why didn't you take account of V-?
 
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That is the general definition of gain.
 
OK.
Vout=Ao(V+-V-), am I right?
Vout=5.8V
V+=69mV
V-= ?
 
Why do you want V- ?
 
  • #10
gleem said:
Why do you want V- ?
So that I can use the formula, Vout=A0(V+-V-) ,and get A0
 
  • #11
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.
 
  • #12
Janiceleong26 said:
So that I can use the formula, Vout=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?
 
  • #13

[ Mentor note: this thread has been tidied up ]
 
  • #14
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
 

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