inverting amp problem help please

 

The most important thing to remember about opamps is that the output will adjust to whatever voltage it takes to make the voltage at the two inputs equal to each other.

hgmjr

 

When the switch is open it will output +10V
When the switch is closed i will output -10V

 

Go ahead and sketch up your own attempts at a solution and then post it here. I am sure you will find many members will be able to assist you in clearing up any confusion you may be encountering.

hgmrjr

 

Here's the formula

 

You have been handed some very good hints from mik3 and joejester. Now is a good time to take a moment and work through the derivation steps to see if you can duplicate their results.

hgmjr

 

thanks mik3, i also got the same answer for b) but i couldn't get the answer for a)
and thanks joejester for giving the actual formula.. i will try to understand how you got to that

 

dizzyuz,

There are two states for the switch, when open you could call it 1 terra ohms or 1 giga ohm, and 1 milliohm when it's closed.

Then you will get the answer or somewhat close to mik's answers.

 

Think in terms of voltages. You know what the voltage is at the noninverting input with the switch in either state. What conditions would apply to match the same voltage on the inverting input.