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# Determine the wavelength.?

A double slit system is used to measure the wavelength of light. With d=15x10^-6 m, L=2.2 m, m=1 and y=7.1cm, find the wavelength.

The equation to use is y=([(lambda)(L)]/d) x m

The book's, the instructor's and my answer are all different. What gives? Rounding error? All range from 420nm to 484nm.

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- kirchweyLv 71 decade agoFavorite Answer
484 nm is correct.

Both your formula (the "small-angle approximation") and the more exact formula:

Θ = arctan(y/L); lambda (exact) = dsin(Θ)/m

agree on this because Θ is indeed small, 1.85 deg. See the ref.

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