CV Raman Effect:
When light rays are incident on materials, the atoms and molecules in the material absorb some energy from incident photons in the light. The light rays are partially reflected, partially refracted, scattered and transmitted. Photos describe the energy, frequency and wave length of light rays. They are like packets of energy with which light travels.
The atoms and molecules in the materials have certain resonant and stable states of energy. These states correspond to different vibrations and rotations of atoms and molecules in space. They absorb energy from photons and get excited to a higher energy state (more vibration or rotation). Then almost immediately, they come back to an energy state a little higher than their previous energy state. So energy is absorbed.
They emit (scatter) light (radiation or photons) back in to the medium. These photons have less energy in them, as some energy is already absorbed by atoms. The difference in the wavelengths of light (photons) scattered corresponds to the energy absorbed. This is characteristic of the material.
Thus CV Raman effect is useful in detecting and analysing the composition of liquids, solids and gases. CV Raman received Nobel prize for this in 1930.
Total Internal reflection :
It is the phenomenon of light rays getting reflected back, when light rays from a denser medium are incident at the interface with a lighter medium at an angle greater than their critical angle.
Mirages in deserts or on hot roads at noon on summer days, transmission of telecommunication signals through fiber optic cables, decorative optical fiber vases.
Total internal reflection phenomenon is used in cameras also. Diamonds shine by this. In total internal reflection, energy of light rays is not lost. So in telecommunications the signals travel very far in optical fibers.
Lenses: Spherical lenses
These are small parts cut from a spherical glass material in the shape of a ball.
Convex or BiConvex lenses:
These converge light rays incident on them to form real inverted images. These also form big virtual images when the objects are closer than the focal length. These are used to correct eye disorders like long sightedness or hypermetropia.
Concave or Biconcave lenses:
These lenses diverge light rays incident on them to form virtual images. These lenses are used to correct shortsightedness or metropia disorder in the eye.
Plano convex lenses:
These converge light rays. They are less converging than biconvex lenses.
Plano concave lenses:
These diverge light rays , but less than biconcave lenses.
These lenses are used to correct astigmatism disorder in the eye. That is distortion by non-uniform magnification of objects in different directions.