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."

    Pot.png

    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.

    Equivalent.png

    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

    Moderator

    Jan 28, 2005
    9,030
    214
    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
    2,039
    287
    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
     
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