[SOLVED] operational amplifier question

[emperror123]

i have a question on this analog electronics

i would like to ask, if we would like to get expression on Vout/ Vin as the attachment show

which they ask V2/Vs in terms of k and Ri

which formula can be form for that

i only get a formula

which is V2/Vs = - R2/R1, but i cant get on what they request

 

[LvW]

Recommendation: Use voltage/current rules applicable to each linear electronic circuit (KCL and superposition principle for two sources).

 

[emperror123]

how about the R2, where to put it?

can show me the example, i dun really understand how to do

 

[LvW]

OK, here is my advice:

Calculate the voltage at node A (Vi) in two steps:
1.) Caused by Vin only (opamp output (controlled source) equal to zero)
2.) Caused by opamp output (input=0).
3.) Use V2=kVi

This is the basic principle of superposition of two signals in a linear network.
From this, it should be possible to derive V2/Vin.

 

[emperror123]

then is it, V2/Vs = -(k*Ri*R1)/(R1*R2+Ri*R2+k*Ri*R1+Ri*R1)

 

[LvW]

Yes, it's correct - if you replace in the numerator R1 by R2 (typing error?).

 

[emperror123]

but question ask is in term of k and Ri?

then the final equation is that too?

 

[keremcant]

but question ask is in term of k and Ri?

then the final equation is that too?

yes, since R1 and R2 are alreasy given quantitatively, just put them in, and this will be the final equation

 

[emperror123]

and last 2 question on this, if they ask 1kOhm for Ri and 1k for k, then just substitute both k and Ri in it, and the R1 and R2 remain the same?

another is if Ri or k or both is infinity, what will be the answer if i substitute it in? is it ignore the k or Ri or both

 

[LvW]

emperror, does this really mean that you do not know how to set a parameter to infinite? It's basic mathematics!

 

[emperror123]

ok now i understand, and the problem bee3n solved
thxx all