Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

How can you get power used from step down transformers

  1. Apr 13, 2005 #1
    Suppose there are two transformers between your house and the high-voltage transmission line that distributes the power. In addition, assume that your house is the only one using electric power. At a substation the primary of a step-down transformer (turns ratio=1:29) receives the voltage from the high-voltage transmission line. Because of your usage, a current of 48 mA exists in the primary of this transformer. The secondary is connected to the primary of another step-down transformer (turns ratio=1:32) somewhere near your house, perhaps up on a telephone pole. The secondary of this transformer delivers a 240-V emf to your house. How much power is your house using? Remember that the current and voltage given in this problem are rms values.

    Im lost :confused:
  2. jcsd
  3. Apr 13, 2005 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Hint: The voltage steps up as you move back towards the High voltage line, and power in equals power out.
  4. Apr 14, 2005 #3
    I dont know if this is right...
    but heres what i did
    Is = IpNp/Ns
    =48*10^-3 * 29 = 1.392A
    Is = IpNp/Ns
    =1.392A* 32 = 44.544A
    P(avg) = Irms*Vrms = 44.544A * 240V = 1.1*10^4W

    is this right?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook