The electron in the hydrogen atom jumps from excited state (n = 3) to its ground state (n = 1) and the photons thus emitted irradiate a photosensitive material. If the work function of the material is 5.1 eV, the stopping potential is estimated to be (the energy of the electron in n^th state E_n = $${{ - 13.6} \over {{n^2}}}eV$$)

The electric field of an electromagnetic wave in free space is given by $$\overrightarrow E = 10\cos ({10^7}t + kx)\widehat j\,\,V/m,$$ where t and x are in seconds and metres respectively. It can be inferred that
(1)  the wavelength $$\lambda $$ is 188.4 m.
(2)  the wave number k is 0.33 rad/m.
(3)  the wave amplitude is 10 V/m.
(4)  the wave is propagating along +x direction.

Which one of the following pairs of statements is correct ?

A condenser of capacity C is charged to a potential difference of V₁. The plates of th condenser are then connected to an ideal inductor of inductance L. The current through the inductor when the potential difference across the condenser reduces to V₂ is

A closely wound solenoid of 2000 turns and area of cross-section 1.5 $$ \times $$ 10^$$-$$4 m² carries a current of 2.0 A. It is suspended through its centre and perpendicular to its length, allowing it to turn in a horizontal plane in a uniform magnetic field 5 $$ \times $$ 10^$$-$$2 tesla making an angle of 30^o with the axis of the solenoid. The torque on the solenoid will be