Thickness of slab

BITSAT 2015 Forum › Optics questions › Thickness of slab

In YDSE both slits produce equal intensities on the screen.A 100% transparent film is placed in front of one of the slits.Now the intensity on the center of screen becomes 75% of previous intensity.The wavelength of light is 6000A and refractive index of glass is 1.5 .Calculate minimum thickness of glass slab.

#Physics #Optics

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4 Answers

1

skygirl ·2009-02-26 23:17:35

previously,

optical path difference = 0 (at the center f the screen)

after film is kept,

optical path diff = Î¼ X (thickness of slab) = Î¼ t [t = thickness of slab , say]
intial intensity = 4I₀ [I₀ = intensity of each slit]

later, intensity bcomes 75% i.e. 3I₀.

Î”Î¸ = Î”x X 2pi/Î» = 2pi . Î¼t/Î» ------------ (1)

intensity = 4I₀cos²(Î”Î¸/2) ----------- (2)

from 1 and 2,

cos (Î”Î¸/2) = Â± âˆš3/2
=> (Î”Î¸/2) = pi/6 , 5pi/6 , 7pi/6 , 11pi/6 .

we can clearly c, t is min for pi/6

so ... finally ..

t = Î»/6Î¼

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1

theking ·2009-03-03 19:43:02

Didi ans is 0.2 Î¼m

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skygirl ·2009-03-04 04:31:51

arey toh ans hi wrong hoga :P

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skygirl ·2009-03-04 04:37:17

arey nahi nahi main hi wrong hoon... :'(

main phirse isme bhi opt path diff Î¼t ley lii...

yahan (Î¼-1)t hoga....

then yes the ans is indeed 0.2Î¼m.

shit.

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