What is the least non zero thickness of a piece of glass with n=1.5, for which destructive interference of rod (650 nm) light in air can take place by reflection?

t = 108.33  nm

Explanation:

we know that for destructive interference we have following relation

for minimum thickness m =0

therefore we have

where

refrective index n = 1.5

putting all value to get required value of thickness

t = 108.33  nm

108.33 nm

Explanation:

For destructive interference the thickness , for minimum m=0

So  

Here is wavelength and n is order of index

So

So the least non zero thickness for destructive interference is 108.33 nm