1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Apparent power, impedance and alternating current.

  1. Apr 21, 2013 #1
    1. The problem statement, all variables and given/known data
    Two serially connected impedances one with [itex]\Phi[/itex] = π/3 and other with [itex]\Phi[/itex] = 0. They have apparent power of S1=S2=200VA. Find total apparent power.

    2. Relevant equations

    S = sqrt(P^2 + Q^2)

    3. The attempt at a solution

    so cosPhi = P1/S1. So P1=cosπ/3*200=100W. For other one P2 = cos0*200=200W. How should I continue? Should I find Q too and derive somehow a equation to sum those powers?
  2. jcsd
  3. Apr 21, 2013 #2
    The complex power, S, delivered to the load is:
    S = S1 + S2

    and the angle between S1 and S2 is the same as the angle between the impedances.

    You want to find the apparent power |S| = |S1 + S2|. If, say:
    S1 = 200∠0
    S2 = 200∠π/3

    Try drawing them in the complex plane. The length of their sum is the answer you're after.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted