How many lines per centimeter does the grating have?
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The light shining on a diffraction grating has a wavelength of 495 nm (in vacuum). The grating produces a second-order bright fringe whose position is defined by an angle of 9.34 degree.
Use the equation, sin(x) = k/d with k = 3, = 495nm (convert to meters) and x = 18.0 degrees. Isolate and solve for d. Once you find d, divide 0.01 by d to get the lines per cm.