Question

Two charged particles, with equal charges of 2.0 × 10⁻⁵ C, are brought from infinity to within a separation of 10 cm. Find the increase in the electric potential energy during the process 

Answer 1

Magnitude of charges, q₁ = q₂ = 2 × 10⁻⁵ C
Initial potential energy = 0
Each is brought from infinity to within a separation of 10 cm.
That is, r = 10 × 10⁻² m 
So, increase in potential energy = final potential energy − initial potential energy.
That is, increase in potential energy,

\[∆ \text{U} = \frac{1}{4\pi \epsilon_0}\frac{q_1 q_2}{r}\]

\[∆ \text{U} = 9 \times {10}^9 \times \frac{2 \times {10}^{- 5} \times 2 \times {10}^{- 5}}{10 \times {10}^{- 2}} = 36\] J