Physics 2 Marks Questions

The red shift in the spectrum of the galaxy indicates that the apparent wavelength is increasing, according to the Doppler effect. This is because the galaxy is moving away from the Earth. That means the universe is expanding.

The importance of Huygens principle is to determine the geometric structure and position of the wavefront from a given position at a later time.
Assumptions : (i) On a given wavefront, which is called the initial wavefront, every point is a source of secondary waves and propagates the disturbance of the original light source in the same way with the same speed in all possible directions.
(ii) The new position of the wave front at any time is obtained by drawing tangents to the secondary wavefronts at that time.

Structure of Polaroid : To produces plane polarized light polaroid is a cheap business trick. It is a film made through a special process which is placed between two glass plates. To make this film, very fine sized crystals of an organic compound harpethite or quinine iodosulphate are spread on a thin sheet of nitrocellulose in such a way that the axes of all the crystals are along the axis. These microscopic crystals are high order dichromates which completely absorb one of the bi-refracted rays.

In longitudinal waves, the direction of oscillation of the particle is in the direction of the wave's travel in the medium, hence compression and rarefaction will pass through the slit in the travel of light waves.

Yes, if white light is used instead of monochromatic light in the double prism or Young's double slit experiment, then the central fringes will be white and the remaining fringes will be colored.

This phenomenon related to light in which the vibrations of the electric vector of light are limited to one direction rather than in all possible directions in the plane perpendicular to the direction of wave propagation, is called polarization of light and light polarized light.

Generally, the size of the obstacle and apertures is of the order of the wavelength of sound waves, not of the order of the wavelength of light waves, hence diffraction of sound can usually be seen. But not of light waves. For diffraction of light, other arrangements have to be made in which the barrier or line aperture or shape is taken to be of the order of its wavelength.

There is no destruction of energy in interference. Only redistribution of energy is takes place. The energy decreases at the places of destructive interference and the energy increases at the places of constructive interference.

Those two sources which emit waves of same frequency or same wavelength and the phase difference between them remains constant with time, are called coherent source.

"In any medium in which a wave is propagating, if we draw a surface on which all the particles located are in the same phase of vibration, then such surface is called 'wave front'." The wave front of a wave in a homogeneous medium is always perpendicular to the direction of wave propagation.