4)The drawing shows a square, each side of which has a length of L = 0.25 m. Two

Question

4)The drawing shows a square, each side of which has a length of L = 0.25 m. Two different positive charges q1 and q2 are fixed at the corners of the square. Find the electric potential energy of a third charge

5)Charges of q and +2q are fixed in place, with a distance of 5.18 m between them. A dashed line is drawn through the negative charge, perpendicular to the line between the charges. On the dashed line, at a distance L from the negative charge, there is at least one spot where the total potential is zero. Find L.
L =

6)Determine the electric potential energy for the array of three charges in the drawing, relative to its value when the charges are infinitely far away and infinitely far apart. (Let

q1 = 7.52 C,

q2 = 19.2 C,

and

q3 = 16.4 C.)

J

Explanation / Answer

Given

   charges q1 = 1.5*10^-9 C, q2 = 4.0*10^-9 C, q3 = -1.35*10^-8 C

we knwo that the potential energy of two charges is U - kq1*q2/r

now the charege q3 is placed at point B , the potential energy is

   U13 = 9*10^9*1.5*10^-9(-1.35*10^-8)/0.25 J = (-7.29)*10^-7J

   U23 = 9*10^9*4*10^-9(-1.35*10^-8)/(sqrt(0.25^2 +0.25^2)) = (-1.3746155826266)*10^-6 J

UB = U13+U23 = (-7.29)*10^-7+(-1.3746155826266)*10^-6 J
   = (-2.1036155826266)*10^-6 J

nwo q3 is placed ta point A

   U23 = 9*10^9*4*10^-9(-1.35*10^-8)/0.25 J = (-1.944)*10^-6 J

   U13 = 9*10^9*1.5*10^-9(-1.35*10^-8)/(sqrt(0.25^2 +0.25^2)) J = (-5.1548084348499)*10^-7 J
UA= (-1.944)*10^-6+(-5.1548084348499)*10^-7 J

= (-2.459480843485)*10^-6 J

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