# vrms value

#### joka2188

Joined Nov 10, 2006
9
A microphone with output resistance of 7kW, is connected to an opamp inverting voltage amplifier whose gain is set at -100 by using resistances of 98 kW and 980 W. If the microphone output is 0.05 Vrms, determine the Vrms value at the output of the opamp.

#### Ron H

Joined Apr 14, 2005
7,014
A microphone with output resistance of 7kW, is connected to an opamp inverting voltage amplifier whose gain is set at -100 by using resistances of 98 kW and 980 W. If the microphone output is 0.05 Vrms, determine the Vrms value at the output of the opamp.
I hope you don't expect a numeric answer. You need to show your work, and ask for feedback.

#### hgmjr

Joined Jan 28, 2005
9,027
Greetings joka2188,

I would recommend you begin the solution to this problem by sketching the circuit. You can replace the microphone by an ideal voltage source that outputs 0.05 Vrms in series with the microphone's internal or source resistance of 7 Kohms.

Once you draw up the circuit, you should be able to apply the equation for the gain of an inverting opamp to find the final answer.

Keep in mind that the internal resistance of the microphone will appear in series with the 980 ohm resistor that is already in place.

HINT: The final voltage gain of the overall circuit will be less than the -100 that is stated in the problem.

With this information in hand, take a stab at an answer and then post it. It would be best if you indicate the basic math you used to arrive at the answer you post.

hgmjr