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 (E_k) 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

37.

The ionisation energy of Li²⁺ is equal to

• 9hcR

• 6hcR

• 2hcR

• hcR

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

• $\frac{{\mathrm{I}}_0}{2}$