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## Suppose light from a 632.8 nm helium-neon laser shines through a diffraction grating ruled at 520 lines/mm. How many bright lines are formed

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## Answers ( )

Answer:1 bright fringe every 33 cm.

Explanation:The formula to calculate the position of the m-th order brigh line (constructive interference) produced by diffraction of light through a diffraction grating is:

where

m is the order of the maximum

is the wavelength of the light

D is the distance of the screen

d is the separation between two adjacent slit

Here we have:

is the wavelength of the light

D = 1 m is the distance of the screen (not given in the problem, so we assume it to be 1 meter)

is the number of lines per mm, so the spacing between two lines is

Therefore, substituting m = 1, we find:

So, on the distant screen, there is 1 bright fringe every 33 cm.