You are designing a lecture demonstration on diffraction gratings. You plan to u

Question

You are designing a lecture demonstration on diffraction gratings. You plan to use light from a laser pointer ( = 473 nm) and shine the light from the grating on the far wall of the lecture room (W = 6.1 m). You want the separation between the central diffraction spot and one of the spots closest to it on the wall to be 1.9 m apart (see figure below). The grating store offers gratings with a specified number of slits per millimeter. How many slits per millimeter do you want for your demonstration? slits/mm

Explanation / Answer

Here

= 473 nm

W = 6.1 m

y = 1.9 m

let the slit seperation is d

Using double slit experiemnt formula

y = wavelength * W/d

1.9 = 473 *10^-9 * 6.1/d

solving for d

d = 1.519 *10^-6 m

d = 1.519 *10^-3 mm

slits per mm = 1/d

slits per mm = 1/(1.519 *10^-3) per mm

slits per mm = 658 per mm

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