E' and E". These two beams if made to overlap will give white light, since what is
absent in one beam is present in the other. A slight increase or decrease in thickness
of the mica plate will change the wavelength or color of the light interfering destructively
and hence change the color of each transmitted beam.
To show that these two colors are complementary it must be shown that the
sum of the two beams gives the original intensity A2• For the Ebeam the components
E' and E" must be combined with their proper phase angle difference.