Power factor

Discussion in 'Homework Help' started by kvi037, May 17, 2013.

  1. kvi037

    Thread Starter New Member

    May 17, 2013
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    0
    Hi,

    I'm struggling with this task for my preperation for a exam next week.
    Can sombody please help me?

    An AC voltage of amplitude 150 volts is impressed across a pure resistance of 100 ohms. Calculate the current and the power dissipation when the frequency of the voltage is 60 cycles/sec.
     
  2. MrChips

    Moderator

    Oct 2, 2009
    12,447
    3,363
    Firstly, we have to make some assumptions.
    When you say amplitude we would assume that to be the value A as in v = Asin(ωt).

    To calculate power, we need to use the rms value.

    The power factor is 1.
     
    screen1988 likes this.
  3. WBahn

    Moderator

    Mar 31, 2012
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    4,800
    The thread title implies that you are looking for the rms values, but the question sounds like you might be looking for instantaneous current and power dissipation. Could you please clarify?
     
  4. WBahn

    Moderator

    Mar 31, 2012
    17,757
    4,800
    Basically correct, but your equation is not consistent with your result.

    You have

    I = 150/0.707*100, which is 21216

    You you should get in the habits of tracking your units throughout your work. So it should be:

    I = Vrms/R = (150Vpk)*(0.707Vrms/Vpk)/(100Ω)
    I = 1.0605 Vrms/Ω = 1.061Arms
     
  5. kvi037

    Thread Starter New Member

    May 17, 2013
    17
    0
    Sorry, I just wrote the calculation in a wrong way.

    Thanks for that you wrote it in the correct way:)
     
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