A cavity of radius r is present inside a solid dielectric sphere of radius R, having a volume charge density of `rho`. The distance between the centres of the sphere and the cavity is a. An electron e is kept inside the cavity at an angle `theta=45^(@)` as shown. the electron (mass m and -e) touches the sphere again after time `((P sqrt(2) mr epsi_(0))/(e a rho))^(1//2)` ? Find the value of P. Neglect gravity.

Answer

6