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Homework Help: Gauss's Law problem

  1. Jan 29, 2004 #1
    Here's the homework problem I'm having trouble with:
    A solid metal sphere of radius .4 m carries a net charge of .190nC. Find the magnitude of the electric field at a point .130 m outside the surface of the sphere.

    I used the equation EA=q/Epsilon_0
    E(4*pi)(r^2)=q/Epsilon_0
    E(4*pi)(.130+.4)^2=(.190E-9)/(8.854E-12)
    E on the right hand side of equation is used to denote scientific notation.
    Solving for the electric field I get 75.748 N/C.
    Am I doing this correctly?
    Any feedback would be appreciated!
     
  2. jcsd
  3. Jan 29, 2004 #2

    chroot

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    Your work looks correct, but your conclusion does not. I think you must have simply made an arithmetic mistake.

    - Warren
     
  4. Jan 29, 2004 #3
    Why does my conclusion seem incorrect?
     
  5. Jan 29, 2004 #4

    chroot

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    Because I don't see how you solved the equation for E and got the value you got. It looks to me like you simply made a mistake in your arithmetic. Make sure you use parentheses appropriately.

    - Warren
     
  6. Jan 29, 2004 #5
    Am I using the correct value for the radius? Should r=.4+.13, r=.4, or r=.13?
    I did make an error in calculations, though. I now get 6.079 N/C.
     
  7. Jan 29, 2004 #6

    chroot

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    I get the same answer.

    - Warren
     
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