parallel beam of light A parallel beam of light from a He-Ne laser, with a wavel

Question

parallel beam of light

A parallel beam of light from a He-Ne laser, with a wavelength 656 nm, falls on two very narrow slits 0.060 mm apart. The interference pattern is viewed on a screen that is 3.6 m away. Let P be the point on the screen that is a distance 5.00 cm away from the central bright fringe. What is the path difference Ar for the wavefronts from the two slits arriving at point P? How many wavelengths is this path difference? What is the phase difference, phi, (in degrees or radians) between the two wavefronts at P? Is P a bright spot, dark spot, or something in between? Explain briefly.

Explanation / Answer

a. path difference = d sino

= 0.060 x 5/squrt (5^2 + 3.6^2)

= 2.3 x 10^ - 7 meters.

b. path difference = n x wavelength

n = 2.3 x 10^ - 7 / 656 x 10^-9 = 0.35

c. phase difference = sin ^-(.0038) = 0.22 degrees.

d. P is a dark spot

because distance from the center is not the integrel multiple of wave length. see part b. n is not integer

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