A point charge `q` is situated at a distance `r` from one end of a thin conduction rod of length `L` having a charge `Q` (uniformly distributed a long its length).find the magnitudes of electric force between the two.

Answer

`1/(4pi in_(0))(qQ)/(d(d+L))`

Explanation

We consider an element of thickness dx at a distance x from q

Force on `q=int1/(4pi in_(0))xx(dQ.q)/x^(2)`
Where `dQ=Q/L dx` then, `F=(KQq)/(L) underset(d)overset(d+L)(int)(dx)/x^(2)=(KQq)/(d(d+L))`