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Homework Help: Electric Power Units

  1. Feb 5, 2008 #1
    Show the quantity volts squared per ohm (V^2/ohm) has SI units of power.

    P = V x I
    P is the power (watt or W)
    V is the potential difference (volt or V)
    I is the current (ampere or A)
    From Ohm’s law
    I = V / R
    R is the resistance (Ohm or Ω).
    So substituting in the above equation
    P = V x (V/R)
    P = V2 /R
    So in unit , watt = (volt)2 / Ω

    I can rewrite, V^2/R = V.V/R = V.I
    From definition of potential difference as Work done per unit charge, V = W/q
    Unit volt, V = unit of W/unitof chaarge = J/C
    Also current = charge/time
    I = C/s
    so, V^2/R = V.V/R = V.I
    = J/C xC/s = J/s
    = watt, (unit of power.)

    Which seems most reasonable?
  2. jcsd
  3. Feb 5, 2008 #2


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    Homework Helper

    You should use the 2nd one as that uses what they gave you V^2/omega to get J/s.
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