Huygen’s Principle

WAVEFRONT The locus of all the particles of the medium, which at

any instant are vibrating in the same phase, is called the wavefront.

Depending upon the shape of the source of light, wavefront can be of the following types:

Spherical wavefront.Cylindrical wavefront.Plane wavefront.

Ray of light: An arrow drawn normal to the wavefront and

pointing in the direction of propagation of disturbance represents a ray of light.

HUYGENS’ PRINCIPLEHuygens’ principle is a geometrical construction, which is

used to determine the new position of a wavefront at a later time from its given position at any instant. In other words, the principle gives a method to know as to how light spreads out in the medium.

Huygens’ principle is based on the following assumptions:Each point on the given or primary wavefront acts as a source

of secondary wavelets, sending out disturbance in all directions in a similar manner as the original source of light does.

The new position of the wavefront at any instant (called secondary wavefront) is the envelope of the secondary wavelets at that instant.

The above two assumptions are known as Huygens’ principle or Huygens’ construction.

INTERFERENCE OF LIGHT The phenomenon of non-uniform distribution of energy

in the medium due to superposition of two light waves is called interference of light.

COHERENT SOURCES Two independent sources of light cannot emit waves

continuously.The waves emitted by two independent sources of light

do not have same phase or a constant phase difference.

PRINCIPLE OF SUPERPOSITION OF LIGHT WAVES YOUNG’S DOUBLE SLIT EXPERIMENT PRINCIPLE OF SUPERPOSITION OF LIGHT WAVES

 

TRANSVERSE NATURE OF LIGHT Longitudinal waves: The waves, in which the particles oscillate

along the direction of propagation of the waves, are called longitudinal waves.

Transverse waves: The waves, in which the direction of oscillation of particles is perpendicular to the direction of propagation of the waves, are called transverse waves.

LAW OF MALUSIt states that when a completely plane polarized light

beam is incident on an analyser, the intensity of the emergent light varies as the square of the cosine of the angle between the planes of transmission of the analyser and the polarizer.

TRANSVERSE NATURE OF LIGHT Longitudinal waves: The waves, in which the particles

oscillate along the direction of propagation of the waves, are called longitudinal waves.

Transverse waves: The waves, in which the direction of oscillation of particles is perpendicular to the direction of propagation of the waves, are called transverse waves.