Atomic Structure

PROPERTIES OF LIGHT

Energy can be transmitted through space in the from of electromagnetic radiation.
Electromagnetic Radiation consists of waves, which have electric and magnetic prosperities. Different forms of electromagnetic radiation, which have different wave lengths and energies, includes, visible light, infrared light, ultraviolet light, radio wave, x-rays etc.
Electromagnetic radiation is like the wave caused by stone thrown in a pond of water, as shown in fig:

1 ) Wavelength (l)
The distance between two successive crests or troughs of a wave in called as wavelength. It is denoted by (l) a Greek letter Lambda . Its units are centimeters, meters and Angstrom:
             

2) Frequency (l):
            The number of waves passing through a certain point in one second is called as frequency. It is denoted by (v) which is a Greek letter nu. It is expressed in Hertz ( Hz)

3) Speed.

            The distance covered by a particular wave in one second is called as speed. It is denoted by “c” its units are centimeter per second.
            The ordinary height is composed of various types of electromagnetic radiation have different wavelengths and frequencies. All of these radiations travel with the same speed. This speed has been determined experimentally which is 3x1010 cm/s. which is equal to 186,000 miles per second. This is in fact considered as the velocity of light.

4)Wave number (  v  ):
            The number of waves (wave lengths) in a unit distance (cm) is called as wave number. It is denoted by  “v” its unite is  wave number is the reciprocal of wave length. It means that greater wavelength will give low wave number as less number of waves can be accommodated in a unit distance.

SPECTRUM

The arrangement of waves of different wavelengths spread out according to the increasing or decreasing of wavelength or frequency is called spectrum. 
The instrument used for studying of spectrum is called on spectrometer. A spectrum has been divided into the types:

1.         Continuous Spectrum: -
When a beam of light passes through a prism, its splits up into different wavelength. When there are no boundaries separating these colour from each other, such spectrum, will be called as continues spectrum .e.g spectrum of ordinary white light is a continuous spectrum:

In the figure a prism is splitting the ordinary white light into different colours (wavelength). The wave with starter wave length will bent at greater angles therefore violet color will be at the bottom of the visible regain.  Below this visible region is ultraviolet wave which is invisible. The light with greater wavelength will be bent at smaller angel.Therefore red colour, with its largest(l) will be at the top of the visible region. Above the red region is the infrared wave, which are invisible and are with l greater then even red colour.                                     RANGE OF WAVE LENGTHS OF VISIBLE SPECTRUM:

2) LINE SPECTRUM:-

            The spectrum in which various wavelength of light are separated from each other by clear boundaries are called as line spectrum. Line Spectrum is also called as atomic spectrum.
            Line spectrum of an element is obtained when an element in the vapours or gaseos state is heated in a flame,  the electrons in atoms are excited and then dexcited releasing the light radiation of characters colour. Colour of light emitted indicates the particulars  wave length  (l)
            Line spectrum may be of two types:-

a.         Line Absorption spectrum:-
When white light containing all wavelength of light is passed through gaseous element sample, some of the wavelengths will be absorbed by the element allowing the other to pass through resulting   in a spectrum containing dark lines. This spectrum is called as line absorption spectrum. As shown in fig:

b.         Line Emission Spectrum: -
            When a substance is heated in a gas discharge tube the light emitted is passed through a prism, the spectrum obtained contains bright lines separated by dark region. This spectrum obtained in called as line spectrum. As shown in the figure: