Obtain an expression for potential energy of a system of two charges in an external field. A system consisting of two charges 7μ C and –2 μC are placed at (-9 cm, 0, 0) and (9 cm,0, 0) respectively in an external electric field E = A (1/r 2 ) where A = 9 × 10 5 C m 2 . Calculate the potential energy of this system.

Question

Philoid · Accepted Answer

Electric field due to charge q at distance r is given by … (i)

Now, the potential due to this charge is given by

… (ii)

Therefore, potential energy of a charge q’ in this potential is given by … (iii)

In the given problem, q = 7μC = 7 x 10^-6 C

q’ = -2μC = -2 x 10^-6 C

Therefore, potential energy of the system