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Need your help guys Rheostat Problem

  1. Sep 24, 2007 #1
    Need your help guys!!Rheostat Problem

    The rheostat is used to control the current to a heating element. The circuit is supplied from source V of 150 V. When the rheostat is adjusted to a value of a 8ohm or less, the heating element can burn out. What is the rated value, in A, of the fuse needed to protect the circuit if the voltage across the heating element at the point of the heating element at the point of maximum current is 145 V?

  2. jcsd
  3. Sep 24, 2007 #2


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    Staff: Mentor

    If I read this correctly, the maximum current would occur when the rheostat is at its minimum voltage, so Imax = 150 V / (8 + Rh).

    And the voltage across the resistive element at Imax = 145V, so find the resistance Rh in terms of those two variables.

    Alternatively, at Imax there is a 150 V supply and 145 V drop across the resistive heater.
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