Value of RF (feedback resistor formula)

[qwerty22]

I need help as I have the answer but I don't know the formula

its an 741, with vi 1Vpp, input resistor is 10k, Value of output signal 10Vpp

I have to work out RF which is 100k, I did the usual **** 1vpp = 10k
10 vpp=10k x 10= 100k
But not the proper formula so I though this:

AV ( idk what it is) = 10v/1v = RF/10k =10

so RF = 10k*10 = 100k

Is that the formula? i need to show proper formula as working out, which i don't know,

however the answer is correct...

I can't seem to find the formula online anywhere btw.

 

[Fish4Fun]

You might look here:

http://www.google.com/url?sa=t&rct=...Xad8l8azzazwTuQ&bvm=bv.56146854,d.eW0&cad=rja

You might also consider posting future homework assignments in the homework section.

Fish

 

[Laplace]

Instead of trying to find the correct formula, why not derive it yourself? Just realize two facts:

1. When the 1 Vp-p input is at +1V the 10 Vp-p output is at -10V.
2. The '-' input to the opamp is a virtual ground. The '+' is tied to real ground and negative feedback keeps the '-' input at the same voltage as the '+' input (within a few microvolts).

So what you have there is a simple voltage divider where 11 volts is divided between Rin and Rf. Solve that and you have the correct formula for finding Rf.