Question

a) You want light at wavelength 527 nm in air to be eliminated by interference upon reflection from a piece of glass coated with a thin film of a transparent substance. For the glass n = 1.53, and for the film n = 1.23. What is the smallest thickness the coating can have? Express your answer in nm (nanometers).

b) Consider a Young’s double-slit experiment. Suppose the slits are separated by 14.2 μm, and each slit is 2.9 μm wide. How many bright fringes (two-slit maxima) are within one of the first side peaks of the diffraction pattern? Your answer should be a whole number. Do not count fringes that exactly coincide with a diffraction minimum, but do count all others.

Answer 1

A) minimumm path differnce in case of interference due to thin film is

because light reflects from denser(n1) medium to rearer's(n2) boundary surface so there must be pi phase difference between interfering rays,

so,

optical path is,

n1 is refractive index of film and t is thickness of film

so,

so minimum thickness

so,from this

2)

so integral there must be 5 bright fringes between two consecutive diffraction peaks.