# Op-Amps help

Discussion in 'Homework Help' started by george102, Oct 21, 2008.

1. ### george102 Thread Starter New Member

Oct 21, 2008
2
0
Last edited: Oct 21, 2008
2. ### hgmjr Retired Moderator

Jan 28, 2005
9,029
218
R2 is not equal to 2.5.

Hint: You know that when dealing with an opamp, the opamp will always tend to drive/adjust its output to a voltage that results in the two input terminals having the same voltage on them.

The problem states that the output voltage of the opamp is to be assumed zero.

All of this means that you know the DC voltage that is applied to the input. You also know the voltage that is on the negative terminal. And finally you know the voltage that you need on the output of the opamp.

You have all of the ingredients for determining the current flowing in R1. And you should know that the current flowing into the negative terminal of the opamp is zero since it has a very high input resistance. That means that all of the current flowing in R1 is going to end up flowing in R2.

Hopefully this helps you solve the problem.

hgmjr

3. ### george102 Thread Starter New Member

Oct 21, 2008
2
0
Thanks solved it: 10k ohms i hope

4. ### hgmjr Retired Moderator

Jan 28, 2005
9,029
218
10K, That's it.

Good Job!

hgmjr