2 charges located in the x-y plane

  • Thread starter Londonfish
  • Start date
  • #1

Homework Statement



Consider 2 charges located in the x-y plane; q1 of magnitude 5 mC (millicoulombs) is located at the origin, and q2 of unknown magnitude is located at (x,y) = (0.1, 0) (in metres). The electric field E at position (0.03, 0.05) is found to be entirely in the +y direction (i.e. the x-component is zero). Determine the sign of charge q1 and the magnitude and sign of charge q2.


Homework Equations



|q| = 5mC (microCoulombs)

F= qE ; q= charge, E= electric Field
E(r) = ƩEi(r)
=1/(4*pi*ε°)*Ʃ(r-ri)*qi/(r-ri)3


The Attempt at a Solution



E1(for one charge)= 1/(4*pi*ε°)*q1/r2
= 1/(4*pi*ε°)* (0.000005 C)/0.0015m
E= 2.996*107

Then I went and did,
E=1/(4*pi*ε°)[(q1/r2)+q2/(r-r2)2]
rearrange for q2 and,
q2= [E(4*pi*ε°)+(r2/q1)](r-r2)2
q2= -29.9997 C. (This seems way to high to be correct)

So q1 is positive to make E in the + y direction.
 
Last edited:

Answers and Replies

  • #2
SammyS
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If q2 is negative, and q1 is positive, then at a location having it's x coordinate between that of the two charges, the electric field would definitely have a non-zero x component.
 
  • #3
Thanks for that. What do you think of the other part of the problem? I'm not quite sure if I'm missing something or did something wrong.
 

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