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Electric field in a cavity in a spherical charge density

  1. May 12, 2017 #1
    1. The problem statement, all variables and given/known data
    A uniform spherical charge density of radius R is centred at origin O. A spherical cavity of radius r and centre P is made. OP = D = R-r. If the electric field inside the cavity at position r is E(r), the correct statement is:
    1)E is uniform, its magnitude is independent of r but its direction depends on r
    2)E
    is uniform, its magnitude depends on r and direction depends on r
    3)E
    is uniform, its magnitude is independent of D but direction depends on r
    4)E
    is uniform and both it's magnitude and direction depend on D.

    2. Relevant equations
    E =
    q2/4πεr2
    Where ε is permittivity of medium.
    Electric flux,Φ= q/ε where q is net charge inside gaussian surface.
    3. The attempt at a solution
    I don't even know where to begin




     
  2. jcsd
  3. May 12, 2017 #2

    kuruman

    User Avatar
    Homework Helper
    Gold Member

    Begin by finding the electric field inside a sphere of uniform volume charge density. Then consider superposition. You get zero charge by adding a positive spherical distribution and a negative spherical distribution so if you add a spherical distribution centered at P of opposite charge, you get a cavity.
     
  4. May 13, 2017 #3
    Thanks. I'll try that
     
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