A student shines white light on a diffraction grating and observes that the…

PHYSICS · Single correct · A Level · Physics · Waves · Waves

Problem

A student shines white light on a diffraction grating and observes that the first-order red (λ=650 nm\lambda = 650\,\text{nm}) maximum appears 9.0 cm to one side of the central maximum on a screen 1.8 m away. Assuming the small-angle approximation is valid, approximately how many lines per millimetre does the grating have? (a) 770 lines mm−1770\ \text{lines mm}^{-1} (b) 77 lines mm−177\ \text{lines mm}^{-1} (c) 38 lines mm−138\ \text{lines mm}^{-1} (d) 154 lines mm−1154\ \text{lines mm}^{-1}

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