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Homework Help: Question on electric filed.

  1. Jun 19, 2010 #1
    NOT HOME WORK QUESTION (itsfrom last year exam question)

    1. The problem statement, all variables and given/known data
    electric field between two disk of radius of R and at distance D=a/2 is given by the following
    n=charge density (Q/A) E_0= the constant 8.85*10^-12

    E=(n/E_o)((1- (a/2)/(((a/2)^2)+(R^2))^1/2

    for what value of the ratio of the plate radius to separation between the plates does the electric field at point x=a/2 deffer by 1percent from the result n/E_o for infinite sheets?
    2. Relevant equations

    the equation for infinite sheet is E=n/2E_o

    3. The attempt at a solution
    not sure how to approach this question
    is it R/2a=0.01 then R/2a*0.01=50?
    please can some one explain this to me!!
  2. jcsd
  3. Jun 20, 2010 #2
    What the question means is that E = 0.99 n / [tex]\epsilon[/tex]

    or it could also be E = 1.01 n / [tex]\epsilon[/tex].

    E is given in terms of a and R, so finding the ratio should not be a problem.

    Are you sure, though, that it is " 1 - a/2 " in the numerator? In this case, finding the ratio would be impossible.
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