Question

A cavity of radius r is made inside a solid sphere. The volume charge density of the remaining sphere is r. An electron (charge e, mass m) is released from rest inside the cavity from point P as shown in figure. The centre of sphere and centre of cavity are separated by a distance a. The time after which the electron again touches the sphere is–

• A. $\sqrt{\frac{6\sqrt{2}r\varepsilon_{0}m}{e\rho a}}$
• B. $\sqrt{\frac{\sqrt{2r}\varepsilon_{0}m}{6\rho a}}$
• C. $\sqrt{\frac{6r\varepsilon_{0}m}{e\rho a}}$
• D. $\sqrt{\frac{r\varepsilon_{0}m}{e\rho a}}$

Answer 1

Answer: (C)

$\sqrt{\frac{6r\varepsilon_{0}m}{e\rho a}}$

Answer 2

E = $\frac { \rho \mathrm { a } } { 3 \varepsilon _ { 0 } }$ F = eE =

Acceleration =

= ×t² = $\sqrt { 2 }$r