# Need some help

Discussion in 'Homework Help' started by mattysoxfan, May 3, 2013.

May 3, 2013
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2. ### mattysoxfan Thread Starter New Member

May 3, 2013
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As far as this problem goes. i'm just starting out, and with the numbers given to me i'm sure i have to apply the resistors numbers with the 1 Volt given to me. I'm just not sure how i'm supposed to get -5 volts.

3. ### #12 Expert

Nov 30, 2010
16,703
7,338
Use the equation for the gain of an inverting op amp. It surely must be in your textbook.

4. ### paulktreg Distinguished Member

Jun 2, 2008
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Have a look here.

5. ### mattysoxfan Thread Starter New Member

May 3, 2013
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So it is inverted. and the 50K resister is giving me the -5. ok that makes much more sense now. wondering how it gave it -5.

6. ### WBahn Moderator

Mar 31, 2012
18,087
4,917
You need to understand how to analyze the circuit and not just how to look up a formula to throw at it. For this circuit, the analysis would proceed as follows:

Q1) Assuming the opamp is operating in its active region, what is the voltage at the inverting input to the amplifier?

Q2) What is the current (magnitude and direction) of the current in the input resistor given an input voltage Vin and the answer to Q1?

Q3) What is the current (magnitude and direction) of the current in the feedback resistor?

Q4) What is the voltage at the output given the answers to Q1 and Q3?

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