Question

For two charges 3C and -3C separated by 1cm and are located at distances 5cm and 7cm respectively from the point P, then the distance between their midpoint and the point P will be

(a) 5.91

(b) 12.6

(c) 2

(d) 9

This question was addressed to me during an internship interview.

I'd like to ask this question from Electric Dipole in section Electrostatic Fields of Electromagnetic Theory

Answer 1

Right answer is (a) 5.91

Explanation: For a distant point P, the R1 and R2 will approximately be equal.

R1 = R2 = r, where r is the distance between P and the midpoint of the two charges. Thus they are in geometric progression, R1R2=r^2

Now, r2 = 5 x 7 = 35. We get r = 5.91cm.