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Homework Help: Gauss's Law - point charge and charged sphere.

  1. Sep 3, 2012 #1
    1. The problem statement, all variables and given/known data

    A point charge q1 = -9.7 μC is located at the center of a thick conducting shell of inner radius a = 2.3 cm and outer radius b = 4.5 cm, The conducting shell has a net charge of q2 = 1.4 μC.

    1) What is Ex(P), the value of the x-component of the electric field at point P, located a distance 8.2 cm along the x-axis from q1?

    2. Relevant equations


    3. The attempt at a solution

    I'm honestly not sure where to start. I tried computing Eq1 at the inner edge of q2, then determining the resulting E at the outer edge of q2 then using that q value and computing E from the outer edge to P. Needless to say I didn't get the right answer.

    Also, I'm new here...Last year (phys 1) I got by well enough to get a B+ in the class, but once we got beyond statics and dynamics and rotional forces (i.e. once we got to electrical/magnetic and hydrostatic forces) I was kind of lost. This year (phys 2) I'm planning to stay on top of things and actually UNDERSTAND the material, not just get a passing grade. Hence the reason I joined this forum - I apologize in advance for any dumb questions - if you see it on here rest assured that I spent at least an hour trying to figure it out on my own.

    Any help is greatly appreciated!
  2. jcsd
  3. Sep 3, 2012 #2
    The field by any spherical conductive shell is the same as that of a point at its center with its total charge.
  4. Sep 4, 2012 #3
    Can you explain that in terms of the equations?
  5. Sep 4, 2012 #4
    If the shell has total charge Q, then the electric field at R from its center is E = K * Q / R^2.

    Observe that this effectively means, in this problem, you have charges q and Q at the center. How would their fields interact?
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