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!

Electric Field and Magnetic Conversion

  1. Jun 15, 2013 #1
    In the solutions of a particular problem, it was stated that:

    <P> = 1/2 |S| = 1/(2μ0) * E^2 / c

    Where <P> is the average power, S is the Poynting vector.

    From the above equation does that mean: B = E /(2μ0c) ?

    I was just wondering how you can show the above relation between Magnetic and Electric field.
    Last edited: Jun 15, 2013
  2. jcsd
  3. Jun 15, 2013 #2


    User Avatar
    Science Advisor
    Gold Member

    No it doesn't. The Poynting vector is [tex]\mathbf S=\frac{1}{\mu_0} \mathbf E \times \mathbf B[/tex]
    and, for a wave propagating in free space, B and E are normal to each other (and to the direction of propagation) and have magnitude [itex]B = \frac{1}{c} E[/itex]. Look it up. When you take a time average to get power, it devolves to your first expression.
    Last edited: Jun 16, 2013
  4. Jun 16, 2013 #3
    Oh ok, thanks.
    Last edited: Jun 16, 2013
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook