# average voltage

#### ARUNA711

Joined Mar 7, 2007
2
HI ,

I just have a doubt in the third chapter of our e-book - operational amplifiers-averager and summer circuit.The formula to get voltage is E=IR.In this chapter to find the average voltage the formula is different.

P Arunachalam

#### Papabravo

Joined Feb 24, 2006
20,369
HI ,

I just have a doubt in the third chapter of our e-book - operational amplifiers-averager and summer circuit.The formula to get voltage is E=IR.In this chapter to find the average voltage the formula is different.

P Arunachalam
Can you provide a link to the e-book or elaborate a bit by telling us how it is different?

#### Dave

Joined Nov 17, 2003
6,969
HI ,

I just have a doubt in the third chapter of our e-book - operational amplifiers-averager and summer circuit.The formula to get voltage is E=IR.In this chapter to find the average voltage the formula is different.

P Arunachalam
I assume this is the section in the e-book which you having issues with?

The maths seems in order to me, which bit are you refering to?

Dave

#### thingmaker3

Joined May 16, 2005
5,083
Looks like Ohm's Law to me...

"The voltage at the virtual ground is now held at 0 volts by the op-amp's negative feedback, whereas before it was free to float to the average value of V1, V2, and V3. However, with all resistor values equal to each other, the currents through each of the three resistors will be proportional to their respective input voltages. Since those three currents will add at the virtual ground node, the algebraic sum of those currents through the feedback resistor will produce a voltage at Vout equal to V1 + V2 + V3, except with reversed polarity."