A light with a second-order bright band forms a diffraction angle of 30.0°. The diffraction grating has 250.0 lines per mm.What is the wavelength of the light?

For a diffraction grating, the bright-band condition is mλ = d sin θ. With 250.0 lines per mm, the spacing is d = 1/250.0 mm = 4,000 nm. For the second-order band, m = 2, and sin 30.0° = 0.5, so λ = (4,000 nm × 0.5)/2 = 1,000 nm. The wavelength is 1,000 nm.

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