# Potentiometer Question

Discussion in 'Homework Help' started by PetrusB, Feb 22, 2010.

1. ### PetrusB Thread Starter New Member

Feb 14, 2010
5
0
"In the following circuit, RL is a potentiometer which varies from 0 to 30 Ohms. Plot (1) The voltage of R2 and (2) the power dissipated by R2."

I understand the overall concept of a potentiometer, and I've read several web sites on them, but I'm still not 100% sure how to use standard nodal or mesh analysis to solve a circuit with a potentiometer and our textbook doesn't address the subject.

Here is what I did. Can someone please tell me if this is correct or not?

I replaced the potentiometer circuit with this second circuit, where the potentiometer is replaced with two separate resistors which resistance values that must sum to 30 Ohms (if one is 5 Ohm the other must be 25 Ohm). This diagram shows 15/15, but it could be two values that sum to 30.

From there, for a given RL setting, I can solve for the current, voltage, and power across R2.

Is this valid? Is there a better way?

2. ### hgmjr Retired Moderator

Jan 28, 2005
9,030
218
Hint: replace the potentiometer with two resistances. One is the variable Rx and the other is the value of the potentiometer minus Rx.

hgmjr

3. ### PetrusB Thread Starter New Member

Feb 14, 2010
5
0
Thanks. That's what I did in the op, but I wanted to be sure. Appreciate the confirmation.

4. ### KL7AJ AAC Fanatic!

Nov 4, 2008
2,181
410
I might add that in the TRUE application of a potentiometer, R2 would either not exist or be of infinite value. As soon as you start drawing current through R2, you no longer have a true potentiometer, but instead, a rheostat.

Just a fine point...but it does simplify things immensely.

eric