Physics

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A film of magnesium fluoride (n=1.38), 1.25x10^-5 cm thick, is used to coat a camera lens (n=1.55). Are any wavelengths in the visible spectrum intensified in the reflected light?
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Bats use the reflections from ultra-high frequency sound to locate their prey. Estimate the typical frequency of a bat's sonar. Take the speed of sound to be 3.40x10^2 m/s, and a small moth 3.00mm across, to be a typical target.

  • Physics -

    answers in the back of the book are
    6.9 x 10^-5 cm

    and

    1.13 x 10^5 Hz

  • Physics -

    Δ=2bn-λ/2 = 2k(λ/2)
    2bn =(2k+1)λ/2
    λ=4bn/(2k+1)
    For k=0,
    λ=4bn=4•1.25•10⁻⁷•1.38=6.9•10⁻⁷m=
    =6.9•10⁻⁵cm
    =============
    λ=3mm=3•10⁻³m
    v=340 m/s
    f=v/ λ=340/3•10⁻³=1.13 x 10⁵Hz

  • Physics -

    Thanks so much Elena !

  • Physics -

    why did you calculatebit as destructive interference? wouldnt we want it to be constructive if we want to intensify the light

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