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
A.
7070
t = nT1/2
10 = n × 20
n = 1/2
we know,
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°
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