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Electric Flux and Gauss's law

  1. Sep 8, 2015 #1
    1. The problem statement, all variables and given/known data
    1)
    A large cube has its bottom face on the x-z plane and its back face on the x-y plane. The corners on the x-axis are at (3.39 m,0,0) and (12.3 m,0,0). The cube is immersed in an electric field pointing in the positive x-direction, and given by:

    E = (91.2x^2 - 2.9)i, x is the distance along the x-axis in m, and E is in N/C.

    Find the net charge Q inside the cube, in μC.

    2)
    There are two hollow, conducting, concentric spheres, with air between the spheres:

    -Sphere 1 is the inner sphere; it has inner radius a = 2.35 mm, outer radius b = 8.53 mm, and carries charge Q1 = -8.41 pC.

    - Sphere 2 is the outer sphere; it has inner radius c = 3.58 cm, outer radius d = 7.92 cm, and carries charge Q2 = 5.84 pC.

    - At the common center is point charge Q = -7.21 pC.

    Find the charge on the outer surface of sphere 2, in pC.
    2. Relevant equations
    ∮E*dA = Q/E0

    3. The attempt at a solution
    Q 1) I try to use equation ∮E*dA = Q/E0 to solve first question, but what I am confusing is the variable E is not a constant, should I plug in the value of x to solve it? and for the surface area since it is a cube, I should count as 6r^2? r is the slice length of the cube.
    Q 2) I guess it is a simple question but I just can not figure out the relationship between two spheres.

    thank you for help.
     
  2. jcsd
  3. Sep 8, 2015 #2

    SammyS

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  4. Sep 8, 2015 #3
  5. Sep 8, 2015 #4

    SammyS

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    What is the electric field within the conducting material itself?
     
  6. Sep 8, 2015 #5
    within the conducting material itself. do you mean inside the inner radius of inner cycle? is it kQ/a^2?
     
  7. Sep 8, 2015 #6

    SammyS

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    I mean: within the conducting material itself, for either of the shells in this problem.
     
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