MHT-CET : Physics Entrance Exam

MHT - CET : Physics - Wave Theory of Light Glossary

·         Huygen's Principle: Every point on a wave front acts as a secondary source and sends out secondary wavelets in all directions. In any given direction, these wavelets travel with the speed of light in that direction. The envelope of the secondary wavelets at any later instant is the new wave front at that instant.

·         Wave Normal: A perpendicular drawn to the surface of a wave front at any point, in the direction of propagation of light, is called wave normal.

·         Ray of Light: The direction in which the light energy is propagated through a medium is called the direction of the ray of light.

·         Wave Front: A wave front can be defined as the surface to all points of which waves of light reach at the same instant so that all the points of the surface are in the same phase.

·         Spherical Wave Front: A wave front originating from a point source of light is called a spherical wave front.

·         Cylindrical Wave Front: If the source of light is in the form of a slit, the wave front originating from it has the shape of a cylinder. Such a wave front is called a cylindrical wave front.

·         Plane Wave Front: A small part of a spherical or a cylindrical wave front originating from a distant source will appear plane and hence it is called a plane wave front.

·         Wave Number: The reciprocal of the wavelength of a light is called the wave number. It represents the number of waves per unit distance.

·         Reflection of Light: When light is incident on the surface of an object, some of the light is returned into the same medium. This phenomenon is called reflection.

·         Refraction of Light: When a ray of light passes obliquely from one transparent medium to another, there is a change in its direction. This change in the direction of a ray of light is called refraction of light.

·         Angle of Incidence: The angle made by the incident ray with the normal to the surface at the point of incidence is called the angle of incidence.

·         Angle of Refraction: The angle made by the refracted ray with the normal to the surface at the point of incidence is called the angle of refraction.

·         Angle of Emergence: The angle made by the emergent ray with the normal to the surface at the point of emergence is called the angle of emergence.

·         Angle of Deviation: The angle between the directions of the incident ray and the emergent ray is called the angle of deviation.

·         Refractive Index: When a ray of light passes obliquely from a medium
a to medium b, if
i is the angle of incidence and r is the angle of refraction,

 the ratio sin i is called the refractive index amb of the medium b with respect to the medium a. sin r

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