Question

(a) Two charges 7 μC and -2μC are placed at (-9 cm, 0, 0) and (+9 cm, 0, 0) respectively. There is no external field on the system. Determine the electrostatic potential energy of this system.
(b) How much work will be done in keeping the two charges at infinite distance from each other?

Answer 1

(a) q₁ = 7μC
q₁ = 7 × 10^-6 C
q₂ = -2pC
q₂ = -2 × 10^-6C
r = 18 cm
r = 18 × 10^-2 m

(b) Potential energy at infinity
U₂ = 0
Potential energy at given position
U₁ = -0.7J
Work done in seperating the charges upto infinite
W = U₂ – U₁
⇒ W = 0 – (-0.7)
W = 0.7 J