Question

A point charge of +10 µC is placed at a distance of 20 cm from another identical point charge of +10 µC. A point charge of -2 µC is moved from point a to b as shown in the figure. Calculate the change in potential energy of the system? Interpret your result.

Answer 1

q₁ = 10μC = 10 x 10^-6 C

q₂ = 2μC = -2 x 10^-6 C

distance, r = 5cm = 5 x 10^-2 m

Change in potential energy,

`Delta "U" = (9 xx 10^9 xx 10 xx 10^-6 xx (- 2 xx 10^-6))/(5 xx 10^-2)`

= -36 × 1 × 10⁹ × 10^-12 × 10² = -36 × 10^-1
∆ U = -3.6 J

Negative sign implies that to move the charge -2pC no external work is required. The system spends its stored energy to move the charge from point a to point b.

∆ U = -3.6 J, negative sign implies that to move the charge -2μC no external work is required. System spends its stored energy to move the charge from point a to point b.