Thin Film Interference
1. An anti -reflective coating is used to coat lenses so that they don’t reflect light. Manufacturers choose to eliminate green light from reflecting off the coated lens, because green is in the middle of the spectrum. A good material to coat the lenses is magnesium fluoride, with a refractive index of 1.38. Find the thickness of a coat of magnesium fluoride on glass (n = 1.45) needed to eliminate 530nm wavelength green light.
2. White light is incident on a thin film of oil (n= 1.63) on a pond of water (n = 1.33). The film is 110nm thick. If the light shines directly down on the film and is reflected back into my eye, what colour do I see most strongly? (Red)
3. Using the information from the previous question, determine what colour is missing from the original white light.
4. The wavelengths of the visible spectrum range from 4.00 x 102 nm to 7.50 x 102 nm. Calculate the range of frequencies of visible light.
(7.50 x 1014 Hz to 4.00 x 1014 Hz)
5. A certain shade of violet has a wavelength of 440 nm in air. If the index of refraction of alcohol relative to air for violet light is 1.40, what is the wavelength of the violet light in alcohol? (3.1 x 10-7 m)
6. A thin layer of glass (n = 1.50) floats on a transparent liquid (n = 1.35). The glass is illuminated by light with a wavelength of 580 nm, in air. Calculate the minimum thickness of the glass, other than zero, capable of producing destructive interference in the reflected light. (1.9 x 10-7 m)
7. A thin film of oil (n = 1.18) is on a puddle of water (n = 1.33). If the film has a thickness of 2.40 x 10-7 m, then what colour of light is strongly reflected in the air?
8. A thin vertical soap film (n = 1.40) is seen to reflect blue light with a wavelength of 462 nm. (Air is on either side of the film.) What is the smallest possible thickness of the film at this point? (8.25 x 10-8 m)