Answer the following question.
Two-point charges q1 and q2 are kept at a distance of r12 in air. Deduce the expression for the electrostatic potential energy of this system.
Solution
Electrostatic potential energy of a system is defined as the total amount of the work done in bringing the various charges to their respective position from infinitely large mutual separation.
Let us consider a charge q1 at a postion vector r1 and q2 at infinity which is to be brought at point P2 having position vector r2. and dW is the small amount of work done in moving a charge to a distance dx.
`dW = vec"F". vecdx`
`dW = -(kq_1q_2)/(r^2). dx`
`W = -int_∞^(r12) (kq_1q_2)/(r^2).dx`
`W = -Kq_1q_2 int_∞^(r12) 1/r^2. dx`
`W = -Kq_1q_2 [-1/r]_∞^(r12)`
`W = Kq_1q_2[1/(r_12)]`
`W = U = (Kq_1q_2)/(r_12)`.
