Question

A thin coating (t = 352.5 nm , n = 1.455) is placed on a glass lens.

PART A: Which visible (400 nm < λ < 700 nm) wavelength(s) will be absent in the reflected beam if the glass has an index of refraction n = 1.350? Express your answer using four significant figures. If there is more than one answer, separate them by a comma.

PART B: Which visible (400 nm < λ < 700 nm) wavelength(s) will be absent in the reflected beam if the glass has an index of refraction n = 1.675? Express your answer using four significant figures. If there is more than one answer, separate them by a comma.

Answer 1

A)

given

refractive index of coating material, n = 1.455

for distructive interefrence

if t is the thickness of the oil,

2*n*t = m*lamda (m = 1,2,3,4,5,.....)

lamda = 2*n*t/m

for m = 1

lamda = 2*n*t/m

= 2*1.455*352.5/1

= 1028 nm

for m = 2

lamda = 2*n*t/m

= 2*1.455*352.5/2

= 524 nm

clearly 400 nm < 524 nm < 700 nm

so, 524 nm light will be absent.

B) same 524 nm

It dose not depend on refractive index of glass.

It depends only on refractive index of coating material.