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Homework Help: Electrostatic force problems, help !

  1. Feb 8, 2010 #1
    Electrostatic force problems, help urgent!

    1. The problem statement, all variables and given/known data

    Question: An isolated hollow metal sphere of radius 40 cm carries a charge of -10*10^-6.
    What is the magnitude of the electric field E (a) in the empty space inside the sphere and (b) 60 cm from the center of the sphere ( no picture provided )

    2. Relevant equations

    Electrostatic force= K * q1*q2/ d^2

    3. The attempt at a solution

    I´ve tried to use Coloumb´s law to get to the correct answer , what im having trouble to realize is 1. is there even an electric field within a hollow sphere,? and 2. do you count the distance in problem B from the surface of the sphere or from the center? I tried the center , and i got the wrong answer, don´t know if that is the problem. HELP URGENT , test coming up! :O :(
  2. jcsd
  3. Feb 8, 2010 #2


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    Science Advisor
    Homework Helper

    Welcome to PF!

    Hi StudentPhys! Welcome to PF! :wink:

    Show us your full calculations, and then we'll see what went wrong, and we'll know how to help! :smile:
  4. Feb 8, 2010 #3
    Re: Welcome to PF!

    My calculations are as follows:
    I went on the assumption, having read it somewhere, that the electric field within a metallic sphere have 0 magnitude. and wrote E=0
    and secondly 2) E= (9*10^9)(-10*10^-6)/ (0,6^2)= 32364 N/C

    Though the key says these answers are incorrect , is this so or is the key wrong?
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