What is the electric potential energy of the group of charge

What is the electric potential energy of the group of charges in the figure?

Solution

The electric potential energy will be the sum of the potential energy of each pair of charges

U = k_e [ (q₁ q₂ / r₁₂) + (q₁ q₃ / r₁₃) + (q₂ q₃ / r₂₃) ]

= 8.99 * 10⁹ [ (1 nC * -2 nC / 0.03) + (1 nC * -2 nC / 0.03) + (-2 nC * -2 nC / 0.03) ]

= 8.99 * 10⁹ [ (-6.667 * 10^-17) + (-6.667 * 10^-17) + (1.33 * 10^-16) ]

= -3.06 * 10^-9 J