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 ?
D.
Accordmng to photoelectric equation
Ek = hv − hv0 ...... (i)
If the energy of photon (hv) is less than the work function (hv0) of metallic surface, then electrons will never be ejected from surface regardless of intensity of incident light.
Also, from Eq. (1), when
v = v0 , Ek = 0
∴ Graph (d) represents variation of Ek with v.
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
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