Afilm of soapy water (n = 1.33) on top of a sheet of plexiglas (n = 1.51) has a thickness of 266 nm. what wavelength is most strongly reflected if it is illuminated perpendicular to its surface? (this is the apparent color of the soapy film.) nm

Wavelength of 1420nm

Explanation: When Ray's are incident perpendicularly the path lenght(difference) = 2t

Where t is the thickness of film given as 266nm.

For reflection to take place and be seen there must be constructive interference. Condition for this is

2t = (wavelength/n of soapy

water)/2

Therefore we have,

4t = wavelength/1.33

Making wavelength subject of formula,

Wavelength = 4*266nm*1.33

= 1.42*EXP{-6} m

= 1420*EXP{-9}m

Wavelength reflected strongly

Is 1420nm.

NOTE: EXP represent 10^

a.   mass number from atomic number