Two insulated charged conducting spheres of radii 20 cm and 15 cm respectively and having an equal charge of 10 C are connected by a copper wire and then they are separated. Then -

(1) Both the spheres will have the same charge of 10 C

(2) Surface charge density on the 20 cm sphere will be greater than that on the 15 cm sphere

(3) Surface charge density on the 15 cm sphere will be greater than that on the 20 cm sphere

(4) Surface charge density on the two spheres will be equal

Two equal charges q are placed at a distance of 2a and a third charge –2q is placed at the midpoint. The potential energy of the system is -

(1) $\frac{q^2}{8\pi {\epsilon }_{0}a}$

(2) $\frac{6q^2}{8\pi {\epsilon }_{0}a}$

(3) $-\frac{7q^2}{8\pi {\epsilon }_{0}a}$

(4) $\frac{9q^2}{8\pi {\epsilon }_{0}a}$

A particle of mass m and charge q is placed at rest in a uniform electric field E and then released. The kinetic energy attained by the particle after moving a distance y is -

(1) $qE{y}^2$

(2) $q{E}^{2}y$

(3) $qEy$

(4) $q^{2}Ey$

How much kinetic energy will be gained by an $\alpha$– particle in going from a point at 70 V to another point at 50 V ?

(1) $40eV$

(2) $40keV$

(3) $40MeV$

(4) $0eV$

If a charged spherical conductor of radius 10 cm has potential V at a point distant 5 cm from its centre, then the potential at a point distant 15 cm from the centre will be -

(1) $\frac{1}{3}V$

(2) $\frac{2}{3}V$

(3) $\frac{3}{2}V$

(4) 3 V

An oil drop having charge 2e is kept stationary between two parallel horizontal plates 2.0 cm apart when a potential difference of 12000 volts is applied between them. If the density of oil is 900 kg/m³, the radius of the drop will be -

(1) $2.0\times {10}^{-6}m$

(2) $1.7\times {10}^{-6}m$

(3) $1.4\times {10}^{-6}m$

(4) $1.1\times {10}^{-6}m$

The ratio of momenta of an electron and an $\alpha$-particle which are accelerated from rest by a potential difference of 100 volt is 

(1) 1

(2) $\sqrt{\frac{2m_e}{m_{\alpha }}}$

(3) $\sqrt{\frac{m_e}{m_{\alpha }}}$

(4) $\sqrt{\frac{m_e}{2m_{\alpha }}}$

When a proton is accelerated through 1V, then its kinetic energy will be -

(1) 1840 eV

(2) 13.6 eV

(3) 1 eV

(4) 0.54 eV