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Homework Help: Power and Resistor problem

  1. Jan 25, 2009 #1
    A blow-dryer and a vacuum cleaner each operate with a voltage of 120 V. The current rating of the blow-dryer is 13 A, and that of the vacuum cleaner is 3.0 A.
    (a) Determine the power consumed by the blow-dryer.
    1 W

    (b) Determine the power consumed by the vacuum cleaner.
    2 W

    (c) Determine the ratio of the energy used by the blow-dryer in 21 minutes to the energy used by the vacuum cleaner in one-half hour.
    Ebd / Evc = 3

    Relevant Equations R=E^2/P

    I mostly get confusedon what E is and what R is in the problem
  2. jcsd
  3. Jan 26, 2009 #2

    Gib Z

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    Homework Helper

    Hello johnson!

    I'm afraid I just don't see how you get yours answers for Part a) and b). Here, we could use the equation [tex]P = IV[/tex], so for eg part a), I get approximately 1.6 kW, not 1 W. I think there may be a misunderstanding here.

    For part c), Power is the rate of Energy per time, ie [tex] P = E/t[/tex]. Rearrang the equation for E (Energy). We can work out how much energy each item takes by then replacing P with the value we got earlier, and t with the time we are told (remember to convert to SI units). Then we can divide appropriately to get the ratio.

    We don't need R anywhere.
  4. Jan 26, 2009 #3
    thanks soo much...i just figured out that I messed up the equations like crazy...i have the right answers now.
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