Monochromatic light of wavelength ? is incident on a pair of slits separated by

Question

Monochromatic light of wavelength ? is incident on a pair of slits separated by 2.00 10-4 m, and forms an interference pattern on a screen placed 2.20 m away from the slits. The first-order bright fringe is 4.40 mm from the center of the central maximum. Calculate the wavelength of the light.

I have the right answer, but I don't know how to get the answer. Please help?

Monochromatic light of wavelength ? is incident on a pair of slits separated by 2.00 page1image840010-4 m, and forms an interference pattern on a screen placed 2.20 m away from the slits. The first-order bright fringe is 4.40 mm from the center of the central maximum. Calculate the wavelength of the light.

Explanation / Answer

dsin@= m lambda

where m is the order of the central maximum here =1

d is the distance between the slits=2*10^(-4) m

tan@ = y/D

given y=4.4 mm

D is the distance between the slits and the screen = 2.2m

for small angles tan@ =sin@

so using both equations we get

lambda = d*m*y/D

=2*10^(-4)*1*4.4*10^(-3) / 2.2

=4 * 10^(-7) m

= 400 nano meters

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