In: Physics
An extremely thin sheet of glass is being inspected at the factory. Illuminated by white light at near-normal incidence, the film-like sheet is 0.402 µm thick and has air on both sides. If the glass has a refractive index of 1.52, what wavelength of visible light (in nm) does it reflect most strongly? (The wavelengths of visible light range from 400 to 700 nm.)
Ques asks for which wavelength of visible light, reflection does strongly. So, for constructive interference, reflection does most strongly. Formula for constructive reflection is used and given values has been put, the thing to be noted here is that in formula, m is order of interference and here we don't know the order, so we have to put different values of 'm' and to check which wavelength comes in visible range.
As shown in solution, by putting value of m=1,wavelength comes out to be 2444.1nm, which is not in visible range. Now, we go on to m =1,wavelength comes out to be 814.7 nm, which is also not in visible range. So, goes to m=2,wavelength comes out to be 488.8 nm, now this wavelength is in visible range. So, 488.8 nm is that wavelength which strongly does reflection.