A point charge q is situated at a distance from one end of a thin conducting rod of length L having a charge Q (uniformly distributed along its length). The magnitude of electric force between the two, is ………………

Options

A. `(2kqQ)/(r(r+L))`
B. `(kqQ)/(r(r+L))`
C. `(kqQ)/(r(r-L))`
D. `(kQ)/(r(r+L))`

Answer

B

Explanation

`dF=(kqdQ)/(x^(2)), dQ=(Q)/(L)dx therefore dF=(kqQ)/(L)(dx)/(x^(2))`
`F=underset(r)overset(r+L)intdF=(kqQ)/(L)underset(r)overset(r+L)intx^(-2)dx=(kqQ)/(r(r+L))`