1. Light from a laser shines through two narrow slits 0.300 mm apart and produces an interference pattern on a screen 4.35 m away consisting of 9 bright fringes over a distance of 6.4 cm. a) Draw a labeled diagram of this scenario and briefly explain how the interference pattern is created b) Calculate the wavelength of the laser. What color is it?

Explanation:

slit separation d = .3 x 10⁻³ m

screen distance D = 4.35 m

fringe width = 6.4 x 10⁻² / 9

= .711 x 10⁻² m

a ) Interference pattern on the screen is created due to interference of two light waves coming from two slits and falling in screen . When they fall on different points on the screen they travel different distance . This is called path difference . When their path difference is equal to their wave length or its integral multiple , they reinforce each other and at that point the brightness increases . On the other hand when at a point the path difference is equal to odd multiple of half wavelength , they kill or destroy each other and darkness is found at that point . In this way dark band and bright band appear on the screen . This is called interference pattern .

b )

Fringe width  = λ D / d

Putting the values

.711 x 10⁻² = λ x 4.35 /  0.3 x 10⁻³

λ = .049 x 10⁻⁵

= 490 x  10⁻⁹

= 490 nm

The colour of this wavelength will be blue .