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Dual Nature of Atom

The emission of characteristic radiation when the salts of certain metals (sodium-yellow, barium-green, strontium-red, etc.) are introduced in the flame has made a great contribution towards the understanding of structure of atoms. In view of this, a brief review of the nature of radiation is in order.

The Wave Nature of Radiation

The movement of mutually perpendicular electrical and magnetic fields in space in the form of wave, as shown in the figure. describes the radiation. Because of the associated electrical and magnetic fields, the radiation is known as electromagnetic radiation.

Electrical and Magnetic components of Light (or Radiation)

Characteristics of Electromagnetic Radiations

The wave motion of an electromagnetic radiation has the following characteristics:
  1. Wave crest
    This is the highest point in the wave. 
  2. Wave trough
    This is the lowest point in the wave. 
  3. Speed
    All electromagnetic radiations travel with the same speed of
    2.997925108 m s-1. It is the horizontal distance that a wave crest or a wave trough travels in one second. It is represented by the symbol c.
  4. Wavelength
    This is the horizontal distance between two corresponding points on a wave. It is represented by the Greek symbol  (pronounced as lambda).
  1. Frequency
    This is the number of wavelengths that pass a fixed point in one second. It is represented by the Greek letter ν (nu, pronounced as new) and is related to speed and wavelength by the expression
    n =           (1.1)
    The unit of frequency is s-1 and the special name hertz (Symbol: Hz) is given to it.
  2. Wave number
    This is the number of wavelengths contained in a unit length. It is represented as  and is given as
  3. Amplitude
    This is the vertical height of the wave at its crest or depth of the wave at its trough. The wave nature of light has been successfully used to explain the phenomena of diffraction and interference. Optical instruments like the microscope and telescope have been designed based on the wave nature of light.

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