# 3 - Interference, Diffraction and Polarisation Questions Answers

what is defination of polarization

**Asked By: SAIFALI SALIM JAMADAR**5 year ago

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**Answer Strategies and trick by Manish sir**(it will help you to solve it by yourself)

Polarisation is the phenomenon to turn light in a particular direction by any means

for an aperture of size a illuminated by a parallel beam of light having wavelength λ the fresnel distance is

ans a^2/λ what is fresnel dist.??

**Asked By: SARIKA SHARMA**6 year ago

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**Answer Strategies and trick by Manish sir**(it will help you to solve it by yourself)

fringe width β = λD/d

for β = d , D is called fresnel distance

so d^{2 }= λD

so D = d^{2}/ λ

now change d by a

A transparent sheet of paper of refractive index 'n' and thickness 't' is pasted on one of the slits in YDSE which uses monochromatic light of wavelength 'x' . How many fringes will cross through the centre if the paper is removed ?

**Asked By: NITIN RAO**6 year ago

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**Answer Strategies and trick by Manish sir**(it will help you to solve it by yourself)

total path difference created by the paper = (n-1)t

geometrical path difference = yd/D

so position of central maxima will be obtained by eq. (n-1)t = yd/D

here y is position of central bright, d is slit appeture and D is distance between slits and screen.

so y = (n-1)tD/d

width of maxima = xD/d , x is wavelength of light

so no. of fringes shifted = [(n-1)tD/d]/[xD/d] = (n-1)t/x