Nature and Source of Light
Wave theory of light
The subject of optics has been divided into two categories that are:
i) Ray Optics
ii) Wave Optics
Ray optics assumed that light consists of rays. A ray of light is the straight line path followed by light in going from one point to another. According to wave theory of light, the light is the form of energy which transfers in a medium in the form of transverse wave motion.
According to wave theory of light, a source of light sends out disturbance in all direction in a homogeneous medium. The disturbance with reach in phase to all the particles of the medium located at the same distance from the source of light and hence, at any instant, these particles must be vibrating in phase with each other.
1. Spherical Wavefront
It is produced by a point source of light as a locus of all such point which are equidistant from the point source, will be a sphere.
2. Cylindrical Wavefront
When the source of light is linear in shape such as a slit, the cylindrical wavefront is produced. All the point equidistant from a linear source lies on the surface of a cylinder.
3. Plane Wavefront
A small part of spherical or a cylindrical wave front due to a distance source will appear plane and hence it is called plane wavefront. It will be represented by a straight line.
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