Electrical Power

Discussion in 'Homework Help' started by Steve1992, Aug 25, 2006.

  1. Steve1992

    Thread Starter Senior Member

    Apr 7, 2006
    100
    0
    eq 1. P = I^2R
    eq 2. P = V^2 / R

    V = 250V
    I = 10A
    P = 2kW

    I get different answers using eq.1 and eq.2. when making R the subject:

    eq 1. R = P / I^2
    = 20 ohms.

    eq 2. R = V^2 / P
    = 31 ohms.

    :confused:
    How do I know which equation to use, when they are suppose to give the
    same answer?

    Steve
     
  2. Dave

    Retired Moderator

    Nov 17, 2003
    6,960
    144
    Your problem is your numbers:

    Remember P = VI

    Therefore P = 250 x 10 = 2500W

    Whereas you have P = 2000W

    If P = 2500W then R = 25 Ohms

    This can be verified by: R = V/I = 250/10 = 10 Ohms

    Dave
     
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