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Homework Help: Non-uniform electric field and conducting spheres

  1. Mar 8, 2014 #1
    1. The problem statement, all variables and given/known data

    Q1. A non-uniform electric field is given by the expression E=3yi+2zj-k.
    Determine the electric field flux through a rectangle in the xy plane, extending from x=0 to x=20 cm and y=0 to y=15cm

    Q2. A point charge q1 = +5nc is placed at the center of a non-conducting sphere (radius a=3) which has a chrage of Q= -8nc distributed uniformly throughout its volume. find:

    a)the electric field at r=2m
    b)the electric field for r=5m

    If the non-conducting sphere is nw replaced with a conducting hollow sphere,having the same total charge, and the same radius. The cavity has a radius of 0.5m FIND:

    C)The electric field at r=2m
    D)The electric field at r=5m

    2. Relevant equations
    Q1. ø=EAcosθ
    Q2. Electricfield x area = Qenclosed/epsilon nod

    3. The attempt at a solution

    My attempts and the all the questions are in the links above

    I would really appreciate some help on this PF.
    Last edited: Mar 8, 2014
  2. jcsd
  3. Mar 8, 2014 #2


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    Welcome to PF !

    You need to post much smaller images than those !
  4. Mar 8, 2014 #3
  5. Mar 8, 2014 #4


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    Staff: Mentor

    I don't understand what you did at Q1. What is 3m? Where is your A, where did you calculate E*A?
    Note that you can simply take the scalar product of the vectors, then the angle is included in the product and you don't have to calculate it.
    As the field is not uniform, you might need an integral.

    For the conducting sphere and r=2m: if the sphere is conducting, where is its charge?
  6. Mar 8, 2014 #5
    Area of the rectangle is 3m
    Could you help me out with solving the integral ?

    For the conducting hollow sphere Question C) at r=2m I tried it again and I think it should be Zero
  7. Mar 8, 2014 #6


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    Staff: Mentor

    3m is a length, not an area. And there is at least one additional error in this result.

    Sure, just write down where you run into problems.

    If that is supposed to be the final result, don't forget the central charge.
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