bright fringe Light central Beam fringe dark fringe Screen Nore: Figure not draw

Question

bright fringe Light central Beam fringe dark fringe Screen Nore: Figure not drawn to scale. Laser light of wavelength is incident on a mask containing two very narrow slits, each of width w, a distance d apart. A screen placed a dis tance L beyond the mask. The photograph shows the pattern of light and dark fringes that appears near the center of the screen. 1. What is the path length difference for two light waves that strike the screen at the point labeled D? Explain. 2. In terms of the wavelength what is the minimum separation distance between the slits? Explain. 3. the wavelength of the incident light is increased, will the location of the bright fringe labeled B move closer to the center, move further from the center, or stay at the same location? Explain. 4. Return to the original situation shown in the photograph. The entire apparatus is now immersed in a transparent fluid having an index of refraction of 1.4. Will location of the bright fringe labeled B move closer to the center, move further from the center, or stay at the same location? Explain. 5. Return to the original situation shown in the photograph. Suppose the screen is moved closer to the double slit. Will the distance between bright fringes B and Cincrease, decrease, or stay the same? Explain.

Explanation / Answer

1)

at point D onstructive fringe is formed and is central bright
fringe

the path difference is zero <-----------answer

2)

the path difference = d*y/L = m*?

y = loation of bright fringe on the screen

y = m*?*L/d

m = order of fringe

m = 1

y1 = 1*?*L/d

m = 2

y2 = 2*?*L/d

fringe width = y2 - y1 = ?*L/d <----------answer

(3)

y is proportional to lambda ?

as the wavelength ? is increased y also increases the B moves
further from the center

(4)

in water wavelength = ?water = ?air/n

ywater = ?water*L/d

ywater = ?air*L/n*d

ywater = yair/n

y water < y air

B moves closer to the center

5)

if the screen is moved the L value decreases

and so the y value decreases

distane between the B and decreases

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