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Voltage fall

  1. Feb 20, 2008 #1
    1. The problem statement, all variables and given/known data

    A refrigerator is marked 80W and 250 V. What is likely to happen if the voltage falls to
    50V?

    2. Relevant equations

    P=V^2/R
    V=IR

    3. The attempt at a solution
    ---------------------------------------------------------
    R=V^2/P
    =250*250/80
    =781.25 ohm
    Assuming the resistance to be constant.
    --------------------------------------------------------
    Current earlier=P/V
    =80/250
    =0.32 A
    ----------------------------------------------------

    Current when voltage falls to 50V

    =50/781.25 (V=IR)
    =0.064 A

    ---------------------------------------------------

    Power will also decrease.
    P=VI
    =50*0.064
    =3.2 W

    ******************************************

    It seems that the appliance will be damaged. I have no idea about anything further. Am I right? I have written everything i could make out. Please help me now.
     
  2. jcsd
  3. Feb 20, 2008 #2

    chroot

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Your reasoning looks entirely correct to me. Of course, in the real world, you're probably right -- the appliance may well be damaged if its compressor can't turn and it just sits there soaking up stall current until it overheats.

    - Warren
     
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