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Gauss law and a metal ball

  • Thread starter kasse
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  • #1
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Homework Statement



A metal ball with radius R = 0,6 m is charged with Q = 0.15 nC. Find the electrical field as function of the distance r from the center of the ball.


The Attempt at a Solution





Gauss law:

Q = e0*E(r)*A = e0*E(r)*4*pi*R^2

which gives

E(r) = Q / e0*4*pi*R^2

I know that inside the ball, the field will be 0. But obviously this is not a function of r...Am I on the right track?
 

Answers and Replies

  • #2
Doc Al
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You're fine.

E(r) = 0 for r<R is perfectly acceptable as a function of r.
 
  • #3
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And outside the ball? I would expext the field to decrease with increasing r, not be constant...
 
  • #4
Doc Al
Mentor
44,882
1,129
And outside the ball? I would expext the field to decrease with increasing r, not be constant...
Right. You have that already done in your first post. (Just change R to r in your equation for E.)
 
  • #5
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0
rajxen

I guess you are correct. The field inside a conductor is zero.

Homework Statement



A metal ball with radius R = 0,6 m is charged with Q = 0.15 nC. Find the electrical field as function of the distance r from the center of the ball.


The Attempt at a Solution





Gauss law:

Q = e0*E(r)*A = e0*E(r)*4*pi*R^2

which gives

E(r) = Q / e0*4*pi*R^2

I know that inside the ball, the field will be 0. But obviously this is not a function of r...Am I on the right track?
 

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