potentiometer circuit

Discussion in 'Homework Help' started by THOMAS, Jan 9, 2004.

  1. THOMAS

    Thread Starter New Member

    Jan 9, 2004
    2
    0
    A potentiometer series circuit contains 2 resistors either side of a slidewire. The slidewire resistance is 20ohms and the supply voltage is 1.38V. If the maximum & minimum tap-off voltages are 9.0mV & 33.0mV respectively, how can I determine the values of R1 & R2??
     
  2. Davis

    Member

    Jan 5, 2004
    13
    0
    Well if I'm understanding your correctly (just look at the diagram below) I would do this.

    Part #1)
    You know that at the potentiometer (POT) lowest position it's going to produce 9.0 mV drop accross R2 and therefore you get the equation 0.009V = I * R2.

    Part #2)
    You know at the potentiometer's highest position there would be a +1.38V - +0.033 Volt drop across R1, which gives you the equation +1.347V = I*R1

    Also, there is a +0.033V across the pot and R2 which gives you the equation +0.033V = I * (R2 + 20ohms), you have R2 + 20ohms because that's the total resistance to ground from the highest position of the pot, which is pots resitance + R2

    Part #3)
    From these two equations solve out for I and R2 by pluging one into the other
    0.009V = I * R2.
    +0.033V = I * (R2 + 20ohms)

    From this equation and using the current found in the previous equations solve for R1
    +1.347V = I*R1

    I hope someone else takes a look over this I could have easily made a simple mistake, however this is the way that I would approach this problem

    - Matt

    Then
    +1.38 V
    \ R1
    /
    \
    /
    |
    |
    |
    |
    \ 33.0mV Max resistance
    / 20ohms Max resistance
    \ <-------
    \
    / 9.0mV Minimum resistance
    |
    |
    |
    |
    |
    \ R2
    /
    \
    /
    GND
     
  3. mozikluv

    AAC Fanatic!

    Jan 22, 2004
    1,437
    1
    :huh: hi,

    pls. try to review your Ohms Law or Kirchoffs Law. the answer is there. ;)
     
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