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ALL CIE PHYSICS DOUBTS HERE !!!
ashwinkandel:
SkyPilotage Virtual earth approximation is only true for inverting op-amp. For an ideal op-amp the gain must be infinite and gain = Vout/Vin. For gain to be infinite the Vin must be zero. So the difference between V+ and V- must be about zero(which only happens if both are same). In case of inverting amplifier one is earthed(P.D=0) so another must also have zero p.d so it is called Virtual Earth. I don't know the answer to second question(which i am also seeking)
SkyPilotage:
I believe you are talking about the open-loop gain, but in non-inv amplifiers, there is a closed loop gain determined by Vout/Vin and it is not infinite. Therefore Vin cant be zero. I have tried looking it up and I found that only the Differential Input Voltage must be zero.
There tends to be confusion between Vin and the Diff. Input volt, where Vin is the voltage coming before the Rin Resistor. While, Diff input voltage is V+-V- which has to be equal to zero. I am not sure why it has to but I think it has -like you said- to with the open-loop gain which has to be infinite, but ill try makin sure.
Thanks for your help mate! ;D
ashwinkandel:
SkyPilotage once check this out(thing that i have attached)
Rvel Zahid:
--- Quote from: ashwinkandel on April 09, 2012, 10:12:36 am ---Rvel Zahid I have attached solutions to your questions:
--- End quote ---
Bombastic Ashwin! Thank you soooooo much, makes things very clear. :)
one more questionhttp://www.xtremepapers.com/CIE/International%20A%20And%20AS%20Level/9702%20-%20Physics/9702_w09_qp_11.pdf
mcq 14 how it is A?
ashwinkandel:
I was a bit unclear last time for q.n 14. Here i have attached another version
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