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Homework Help: Circuit indicator problem

  1. Mar 25, 2008 #1
    could anyone help me with this problem?

    1. The problem statement, all variables and given/known data

    An automobile gasoline gauge is shown schematically in Figure 27-61. The indicator (on the dashboard) has a resistance of 10 . The tank unit is a float connected to a variable resistor whose resistance varies linearly with the volume of gasoline. The resistance is 200 when the tank is empty and 30 when the tank is full.


    *Find the current when the tank is half-full*

    2. Relevant equations

    V=IR

    3. The attempt at a solution
    the current when the tank is empty is 12=I*200. so i multiplied that by two to get the answer but it was incorrect. i also tried to plug 15 into the equation since it's half of thirty but that too was wrong
     

    Attached Files:

    Last edited: Mar 25, 2008
  2. jcsd
  3. Mar 25, 2008 #2
    First let's make a little chart to describe the variable resistor:

    200 ohms ...... tank empty
    ??? ohms ...... tank half-full
    30 ohms ....... tank full

    What number should I replace those question marks with?
     
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