51.

A and B are two metals with threshold frequencies 1.8 x 10¹⁴ Hz and 2.2 10¹⁴ Hz. Two identical photons of energy 0.825 eV each are incident on them. Then photoelectrons are emitted by (Take h = 6.6 x 10^-34 J-s)

• B alone

• A alone

• Neither A nor B 

• Both A and B

Electrons in a certain energy level n = n₁ can emit 3 spectral lines. When they are in another energy level, n=n₂ they can emit 6 spectral lines. The orbital speed of the electrons in the orbits are in the ratio

• 4 : 3

• 3 : 4

• 2 : 1

• 1 : 2

In Young's double-slit experiment with sodium vapor lamp of wavelength 589 nm and the slits 0.589 min apart, the half angular width of the central maximum is

• sin^-1(0.01)

• sin^-1(0.0001)

• sin^-1(0.001)

• sin^-1(0.1)

A radioactive element forms its own isotope after 3 consecutive disintegrations. The particles emitted are

• 3 β-particles

• 2 β-particles and 1α-particle

• 2 -βparticles and 1 γ-particle

• 2 α-particles and 1 β-particle

A radioactive substance contains 10000 nuclei and its half-life period is 20 days. The number of nuclei present at the end of 10 days is

• 7070

• 9000

• 8000

• 7500

The principle of LASER action involves

• amplification of particular frequency emitted by the system

• population inversion

• stimulated emission

• All of the above

A ray of light is traveling from glass to air, (refractive index of glass= 1.5). The angle of incidence is 50°. The deviation of the ray is

• 0°

• 80°

• $50° - {\sin }^{-1}\left[\frac{\sin 50°}{1.5}\right]$

• ${\sin }^{-1}\left[\frac{\sin 50°}{1.5}\right] - 50°$

When the angle of incidence is 60° on the surface of a glass slab, it is found that the reflected ray is completely polarised. The velocity of light in glass is

• √2 x 10⁸ ms^-1

• √3 x 10⁸ ms^-1

• 2 x 10⁸ ms^-1

• 3 x 10⁸ ms^-1

In a reverse-biased diode when the applied voltage changes by 1 V, the current is found to change by 0.5 µA. The reverse bias resistance of the diode is

• 2 × 10⁵ Ω

• 2 × 10⁶ Ω

• 200 Ω

• 2 Ω

Through which mode of propagation, the radio waves can be sent from one place to another?

• Ground wave propagation

• Sky wave propagation

• Space wave propagation

• All of the above