Two point charges of 1 nC and 2 nC are placed at the two corners of equilateral triangle of side 3 cm
Q. Two point charges of 1 nC and 2 nC are placed at the two corners of equilateral triangle of side 3 cm. The work done in bringing a charge of 3 nC from infinity to the third corner of the triangle is ____ μJ.

1 / (4πϵ0) = 9 × 109 N·m2/C2

(A) 3.3

(B) 27

(C) 2.7

(D) 5.4

Correct Answer: 2.7

Explanation

Work done in bringing a charge from infinity is equal to the electric potential at that point multiplied by the charge.

V = k (q1/r + q2/r)

Here,

q1 = 1 nC,   q2 = 2 nC,   r = 3 cm = 0.03 m

V = 9×109 × (3×10−9 / 0.03) = 900 V

Work done:

W = qV = 3×10−9 × 900 = 2.7×10−6 J

W = 2.7 μJ

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