Diketahui 

q1 = 20mC = 20 x 10^-3

q2 = 24mC = 24 x 10^-3

r = 12 cm = 12 x 10^-2

k = 9 x 10^9

Ditanya : F = ?

Jawab: 

F = k x q1 x q2 / (r^2) 

F = (9 x 10^9) (20 x 10^-3) (24 x 10^-3) / (12 x 10^-2)^2

F = 9 x 20 x 24 x 10^-3 / 12 x 12 x 10^-4

F = 30 x 10^7

F = 3 x 10^8 N