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: Electric field

  1. May 22, 2005 #1
    Given E in a region of space ( [tex]\epsilon_{o} , \mu_{o}[/tex])
    I should think of it as a free space or vacuum?
     
    Last edited: May 22, 2005
  2. jcsd
  3. May 22, 2005 #2
    This is vacuum.
     
  4. May 22, 2005 #3
    I have to find [tex]B[/tex], [tex]\rho[/tex] and [tex]J[/tex]

    [tex] \nabla \times \vec E= -\frac{\partial \vec B}{\partial t} [/tex]

    [tex] \nabla \cdot D=\rho [/tex]

    In free space J = 0 so for J in vacuum I should use

    [tex] \nabla \times H =J+ \frac{\partial D}{\partial t}[/tex]

    or something else?
     
  5. May 23, 2005 #4

    OlderDan

    User Avatar
    Science Advisor
    Homework Helper

    You probably want to use

    [tex]D = \epsilon_{o} E [/tex]

    [tex]B = \mu_{o} H, [/tex]

    to eliminate D and H. Don't know if you will need it, but you can round out your set of equations with

    [tex] \nabla \cdot B=0 [/tex]
     
  6. May 23, 2005 #5
    I think I got B, D, H and [tex] \rho[/tex] and using

    [tex] \nabla \times H =J+ \frac{\partial D}{\partial t}[/tex]

    I get J

    What is the difference between free space (J = 0) and vacuum?
     
  7. May 23, 2005 #6

    dextercioby

    User Avatar
    Science Advisor
    Homework Helper

    Vacuum means [itex] \mu_{0},\epsilon_{0} [/itex].If you're speaking about "free space",then u should assume no charge density [itex] \rho=0 [/itex] and no charge transport [itex] \vec{J}=0 [/itex].

    So we can have sources in vacuum.But not in free space.

    Free space is typically a vacuum in which electromagetic waves (radiation far away from the sources) propagate.

    Daniel.
     
  8. May 23, 2005 #7
    Thanks, So in my problem I will get J not equal 0
     
  9. May 23, 2005 #8

    dextercioby

    User Avatar
    Science Advisor
    Homework Helper

    Please post the text of your problem in its exact form.

    Daniel.
     
  10. May 23, 2005 #9
    In the region of space [tex]\epsilon_{o} , \mu_{o}[/tex]
    [tex]E = (6z\vec{i}+10y\vec{j})cos500t \vec{j}[/tex]

    Find [tex]B, \rho, J[/tex]
     
  11. May 23, 2005 #10

    dextercioby

    User Avatar
    Science Advisor
    Homework Helper

    [tex] \nabla\cdot\vec{E}=\frac{\rho}{\epsilon_{0}} [/tex] (1)

    [tex] \nabla\times\vec{E}=-\frac{\partial\vec{B}}{\partial t} [/tex] (2)

    [tex] \nabla\times\vec{B}=\mu_{0}\vec{J}+\mu_{0}\epsilon_{0}\frac{\partial\vec{E}}{\partial t} [/tex] (3)

    Daniel.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook