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^What is visible light

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^What is visible light

EM-radiation that can be detected by the human eye is called white light or simply visible light. It is mainly through visible light and the sense of vision that we know and interpret the world around us. Sensation of colour of light perceived by the human eye is determined by its frequency of the wave falling on ratina cells and not on its wavelength.

Visible light is a mixture of photons of wavelengths from 380 nm to 780 nm in appropriate proportion. Following table displays the wavelength range for colours.

In terms of micrometer (μm) & angstroms (A0) we can write 570 nm = 0.57 μm = 5700 A0

^Quantum optics

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^Quantum optics

Quantum optics treats light as a particle (localised energy packet) called photon’ to deal with photoelectric effect, Raman effect & LASER, etc.

^Wave optics

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^Wave optics

Light behaves as a wave when the size of obstacle is comparable with the wavelength of light. Wave optics branch explains the following phenomena

  1. Interference (i.e. non uniform distribution of energy when two or more light waves superpose)
  2. Diffraction (i.e. bending & spreading of light wavefronts on encountering obstructions of size comparable or smaller than its wavelength)
  3. Polarisation (i.e. restricting the vibrations of light to one plane)

^Geometrical optics

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^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 optics?

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^What is optics?

The branch of Physics which deals with light, it’s nature, cause, source, properties & it’s effects is called Optics.

^What is light?

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^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.

^Electromagnetic Force

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^Electromagnetic Force

EM – force acts between charged particles. It binds electrons with nuclei to form atoms & binds atoms together to form molecules. It is responsible for the properties of solids, liquids, & gases. Force of attraction/repulsion between two static charges is described by the Coulomb’s law i.e

Electric forces and magnetic forces were considered to be separate forces until the 1860s when James Clerk Maxwell was able to demonstrate that they were different manifestations of the same force – the electromagnetic force. Infact, all contact forces such as: Frictional force (f), Viscous force (Fv), Air drag (fd) Spring force (Fspring or Fr), Normal reaction (N), Tension force in ropes, strings & muscles (T), Buoyant force (B or U), Surface tension force (FS) are actually due to the electromagnetic force.

^Maxwell equations

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^Maxwell equations

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

^ γ-rays

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^γ – rays

(a) Produced in nuclear reactions and are also emitted by radioactive nuclei (such as Co 60 & Cs 137).

(b) Properties: Effect on photographic plate, fluorescence, ionization, diffraction, high penetrating power & can cause serious damage if absorbed by living tissues.

(c) Used

  1. in radio therapy to treat certain cancers and tumors
  2. to produce nuclear reactions
  3. to study the atomic nuclei.

^Ultraviolet light

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^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.

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