What is light ? Part 3 WAVE THEORY OF LIGHT

Thomas young consolidated the idea that light is a wave motion which he believed was excited luminiferous ether that prevade the universe such ideas had been discussed by hook and others over a century before but young was the first recognized an important property not only of light but of wave motion in general. This is the principle of superposition which states that when two or more wave cross the size of resulting wave at each point is given by simply adding together size of the individual waves at that
 Point. 

This principle is revealed in an experiment first performed by young in which light falls on a card with two very narrow silts that are not far apart at tomorrow beams of light emerging through the holes illuminate a screen beyond as the beams of light originate from the same initial beam there wave motions should be in face in (duating in Unison) according to the supervision principal at point where the light takes part of different lens to reach the screen the separate in undulation can be out of face as the trough in one wave varies at the same time as the peak  of in other the two waves therefore cancel Each Other how to give darkness at the screen this is confirmed by the pattern of alternating bright and dark stripes that appears on the screen the bright stripes correspond to wear the difference in the parts equal and exact number of wavelength so that the separate beams rain force each other the intermedited dark regions are where the two waves can cancel each other .

Such bright and dark band occur when the two silt experiment is performed with monochromatic light of one spectral colour with white light the pattern produce is a complex series of bands of different colour this is because the reinforcing and cancelling offers at different points on the screen for different parts of spectrum and it shows that light of different colours has different wavelength the different in two part and necessary to reinforce or cancel the light must be slightly different for each colour.  It is for to understand the  difference of  colour .

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