Question

Three charges Q, + q and + q are placed at the vertices of an equilateral triangle of side ℓ as shown in the figure. It the net electrostatic energy of the system is zero, then Q is equal 

(A) – q 

(B) + q 

(C) Zero 

(D) – (q/2)

Answer 1

The correct option (D) – (q/2)

Explanation:

Potential is zero means system is in equilibrium.

∴ k[{(Q ∙ q)/ℓ} + {(Q ∙ q)/ℓ} + {(q ∙ q)/ℓ}] = 0------ as PE = [(kQ₁Q₂)/r]

∴ 2qQ + q² = 0

q(2Q + q) = 0

∴ q = – 2Q

Q = – (q/2)