Current in a coil changes from 4 A to zero in 0.1 s and the emf induced is 100 V. The self inductance of the coil is
0.25 H
0.4 H
2.5 H
4 H
Two identical charges repel each other with a force equal to 10 mg wt when they are 0.6 m a part in air (g = 10 ms-2). The value of each charge is
2 mC
2 × 10-7 C
2 nC
2 μC
The potential of the electric field produced by point charge at any point (x, y, z) is given by V =3x2 + 5, where x, y are in metres and V is in volts. The intensity of the electric field at (−2, 1, 0) is
+ 17 Vm-1
− 17 Vm-1
+ 12 Vm-1
− 12 Vm-1
The potential of a large liquid drop when eight liquid drops are combined is 20 V. Then the potential of each single drop was
10 V
7.5 V
5 V
2.5 V
Which one of the following graph represents the variation of maximum kinetic energy (Ek) of the emitted electrons with frequency v in photoelectric effect correctly ?
A and B are two metals with threshold frequencies 18 x 1014 Hz and 2.2 x 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
B.
A alone
Threshold energy of A is
Similarly, EB = 0.91 eV
Since, the incident photons have energy greater than EA but less than EB. So, photoelectrons will be emitted from metal A only.
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
The electromagnetic theory of light failed to explain
photoelectric effect
polarisation
diffraction
interference
Light from two coherent sources of the same amplitude A and wavelength λ, illuminates the screen. The intensity of the central maximum is I0. If the sources were incoherent, the intensity at the same point will be
4I0
2I0
I0