The thinnest film in which the reflected light will be a max

AI Thread Summary
The discussion revolves around determining the thinnest film that produces maximum reflected light for monochromatic light striking at normal incidence. The consensus indicates that a film thickness of λ/4 is correct, despite initial confusion regarding the phase shifts at the boundaries. Participants suggest that the problem may have overlooked the 180° phase shift occurring at the air-film interface. There is speculation that the film's index of refraction could influence the expected results. Ultimately, the thinnest film for maximum reflection is confirmed to be λ/4.
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Homework Statement


Monochromatic light, at normal incidence, strikes a thin film in air. If λ denotes the wavelength in the film, what is the thinnest film in which the reflected light will be a maximum?


  • A

    λ/4


  • B
    3λ/4


  • C
    λ

  • D

    much less than λ


  • E

    λ/2

Homework Equations


n air ∠ n glass
so at the first reflection it will cuase a 180° ray out of phase while the second ray reflected from the inside it will stay inphase because n air ∠ n glass
so for constructive interference: 2L=odd number*λ/2

The Attempt at a Solution


least odd number is one , so L=λ/4 ?? why it is incorrect
 
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Your answer of λ/4 is correct. The problem statement does not mention glass.
 
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Well all I can do is sympathize. 1/4 should have been correct. Perhaps they have in mind a low index film on a high index substrate? Or perhaps the problem setter forgot about the 180 phase shift front to back and just got it wrong.
 
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Any Help said:
the thinnest film in which the reflected light will be a maximum[/color] minimum[/color] ?
possibly intended
 
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