Wavelength and colour
The colour of light is related to the frequency and therefore to the wavelength of the light waves if they are passing through the same medium. The wavelength increases as we go from violet towards the red end of the spectrum. The wavelength of red
light is approximately twice that of violet. Returning to Young’s experiment, it is clear from the equation A = ax D
that if a and D are constant, then }, ex: x or, in words, the fringe spacing is proportional to the wavelength.
A very good way of demonstrating this is to make a triple light filter from three horizontal strips of red, green, and blue gelatine. A white light source is used in this experiment and the light filter is placed just in front of the fringe area on the screen or just in front of the eyepiece. Red has the longest, and blue the shortest wavelength of the three colours and the resulting appearance of the fringes is as in Fig. 26.15.