Opamp problem

  • #1
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-)
 

Answers and Replies

  • #2
gleem
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Isn't the gain of this amp Vout/VR?
 
  • #3
gleem
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But Vout and VR are given.
 
  • #4
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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  • #5
gleem
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There is no zero in my equation in post #2
 
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  • #6
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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  • #7
gleem
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That is the general definition of gain.
 
  • #8
OK.
Vout=Ao(V+-V-), am I right?
Vout=5.8V
V+=69mV
V-= ?
 
  • #9
gleem
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Why do you want V- ?
 
  • #11
gleem
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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
LvW
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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
NascentOxygen
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[ Mentor note: this thread has been tidied up ]
 
  • #14
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
 

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