How to Determine V- Without Knowing Resistance?

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Discussion Overview

The discussion revolves around determining the voltage V- in a circuit where the resistance is unknown. Participants are exploring how to calculate V- given that V+ is known and the output voltage (Vout) is provided. The context includes a focus on gain calculations in amplifier circuits.

Discussion Character

  • Homework-related
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant states that V+ is 69mV and questions how to determine V- without knowing the resistance of X.
  • Another participant suggests that the gain of the amplifier can be expressed as Vout/VR.
  • There is a clarification request regarding the assumption that V- equals zero in the gain equation.
  • Some participants discuss the general definition of gain and its application to the problem.
  • Multiple participants express confusion about whether the focus is on the gain of the circuit or the op-amp specifically.
  • There is a repeated emphasis on the need to find V- to use the formula Vout=A0(V+-V-).

Areas of Agreement / Disagreement

Participants do not reach a consensus on the role of V- in the gain calculation, and there are competing views on whether the question pertains to the gain of the circuit or the op-amp. The discussion remains unresolved regarding the determination of V-.

Contextual Notes

There are unresolved assumptions about the definitions of gain and the specific circuit configuration being discussed. The relationship between Vout, V+, and V- is not fully clarified, and the implications of unknown resistance are not addressed.

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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But Vout and VR are given.
 
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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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