^Geometrical optics

Geometrical optics is also called ray optics. It treats propagation of light in terms of rays and is valid only if wavelength of light is much lesser than the size of obstacles. It deals with the following phenomena

1. rectilinear propagation (i.e. light propagates in a straight line, due to its small wavelength)
2. reflection (i.e. coming back in same medium on striking a shining surface)
3. refraction (i.e. change of speed on changing transparent medium)
4. dispersion (i.e. light splits up in to its constituent colours on changing transparent medium)
5. image formation ( i.e. intersection of two or light rays after undergoing reflection or refraction).

^What is light?

In general light means following three parts

1. Infra red radiation or thermal radiations
2. visible light
3. ultraviolet light,

As these are parts of EM spectrum, thus light is electromagnetic, thus properties of light are same as that of any EM wave. Light can behave like a ray, a wave & as a particle, depending on its interaction with the objects it encounters on its way.

^Maxwell equations

Following five equations give a complete description of all em– interactions and are called Maxwell eq:

^Ultraviolet light

(a) Produced by special lamps like mercury and iron are lamps and by very hot bodies like sun.

(b) Properties: Effect on photographic plate, fluorescence, ionization, highly energetic, tanning of the human skin.

(c) Used

1. To destroy bacteria and for sterilizing the surgical instruments
2. In the detection of forged documents finger prints
3. In burglar alarms etc as they can cause photoelectric effect.
4. For studying fluorescence
5. In the study of molecular structure and arrangement of electrons
6. To prevent the food stuff.

^Infra red waves

(a) Also called heat waves & are produced by hot bodies and molecules.

(b) Properties: Heating effect, reflection, refraction, diffraction & propagation through fog.

(c) Used

1. In taking photographs during the conditions of fog, smoke etc. as these waves are scattered less than visible rays and hence can travel longer distances through atmosphere under fog, smoke etc.
2. In weather forecasting
3. In checking the purity of chemicals
4. In the study of molecular structures
5. For producing dehydrated fruits
6. In green houses to keep the plants warm
7. To provide electrical energy to satellites using solar cells.
8. To treat muscular strain.
9. In solar water heaters and cookers.