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Homework Help: DC circuits

  1. Mar 23, 2004 #1
    Hi all,

    I really need somebody to explain to me how to work the following problem...

    A 1.50E2 - W heater is designed to operate with an EMF of 120V. If the potential difference across the heater changes by a small amount such as 2.6%, approximately by what factor does the power change? (Hint: approximately the changes with differentials) (unit %).

    can somebody kindly explain to to go about it?? thanks
  2. jcsd
  3. Mar 24, 2004 #2

    Doc Al

    User Avatar

    Staff: Mentor

    The first step is to express the power as a function of voltage. That should be easy. Then you have P = f(V).

    Then you approximate the changes as follows:

    ΔP = f'(V)ΔV

    You can then manipulate this equation to give you the relationship between ΔP/P and ΔV/V. Give it a try.
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