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On non linear resistor and how to calculate a fixed resistor.

  1. Sep 25, 2011 #1
    1. The problem statement, all variables and given/known data

    The current in amperes through a certain type of non-linear resistor is given by I=0.05V^3, where V is the potential difference in volts across the resistor. This resistor is connected in series to a fixed resistor and a constant voltage source of 9V is connected across the series combination. What value of resistance should the fixed resistor have so that a current of 0.40A flows ?

    2. Relevant equations
    V=IR and P=VI ?



    3. The attempt at a solution
    I first tried to calculate the total resistance which gives 22.5 ohms. But I do not know how to calculate the non-linear resistor as it does not obey ohm's law hence no proper formula can be used ? Please help.

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



    2. Relevant equations



    3. The attempt at a solution
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Sep 25, 2011 #2

    gneill

    User Avatar

    Staff: Mentor

    Suppose that, as stated, a current of 0.40A is flowing through the nonlinear resistor. What will be the voltage drop across it according to the given formula for it (you may have to rearrange the formula)?
     
  4. Sep 25, 2011 #3
    By I=0.05V^3, when I=0.40A, V=2V. Hence voltage drop across the fixed resistor is 9-2=7V.
    Therefore by V=IR, 7=0.4R,
    Therefore R=17.5 ohms

    Am I right ?
     
  5. Sep 25, 2011 #4

    gneill

    User Avatar

    Staff: Mentor

    Looks good!
     
  6. Sep 25, 2011 #5
    Thanks a lot !
     
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