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

20. [1pt]

A 30.6- cm-diameter conducting sphere is charged to 538 V relative to V = 0 at r =infinity. What is the surface charge density sigma?

Correct, computer gets:3.11E-08 C/m^2 = Sigma, r=.153

21. [1pt]

At what distance will the potential due to the sphere be only 11.0 V?

2. Relevant equations

[tex]E=\sigma / \epsilon_{0} and

E=V/r[/tex]

3. The attempt at a solution

I already found sigma for Question number 20, and for 21 I am trying the same method, but am just solving for r.

so I got [tex]r=(V/\sigma) *\epsilon_{0} [/tex]

and everytime I do it I come out with r=0.00313 m which is smaller than the initial r, even though I know from this statement "538 V relative to V = 0 at r =infinity" that if V is smaller r must be bigger.

What am I missing? Thanks in advance

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# What is the surface charge density sigma?

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