# Physical Optics

## Physical Optics Notes for Class 11 - 12

Poynting vector

The amount of energy passing through unit area placed perpendicular to direction of a electromagnetic wave propagating is called poynting vector.

Wave front

At any moment, locus of particles on a wave which are in phase is called wave front.

Plane wave front

Locus of particles which are in phase or parallel rays coming from infinity is called plane wave front.

Slit

The small rectangular opening which has long length but a very small width is called slit.

Coherent source

Two light sources are said to be coherent if they emit waves having constant phase difference.

Interference fringe

When interference takes place on a plane or screen, some parallel bright and dark lines or pattern are found. This bright or dark patterns are called interference fringes.

Diffraction

The spreading of light rays passing through narrow opening or around corner is called diffraction of light.

Fresnel's class of diffraction

Light source at finite distance emits light rays and when they travel round the corner and creates a fringe pattern on screen placed at finite distance. This pattern is called fresnel's class of diffraction.

Fraunhofer class of diffraction

Light rays coming from infinity creates a pattern on screen at infinity. It is called Fraunhofer class of diffraction.

Diffraction grating

A plastic slide having large number of equidistant slits used for measuring wavelength of light is called diffraction grating.

Grating constant

If width of each slit of a grating is a and each opaque scratch has width of b, (a+b) is called grating constant.

Polarization

The process by which vibration of light of wave can be confined in a definite plane is called polarization.

No Comment