A. Distinguish between unpolarized light and linearly polarized light. How does one get linearly polarised light with the help of a polaroid?
B. A narrow beam of unpolarized light of intensity 
is incident on a polaroid 
The light transmitted by it is then incident on a second polaroid 
with its pass axis making angle of 60o relative to the pass axis of 
Find the intensity of the light transmitted by 
.
OR
A. Explain two features to distinguish between the interference pattern in young’s double slit experiment with the diffraction pattern obtained due to a single slit.
B. A monochromatic light of wavelength 500 mm is incident normally on a single slit of width 0.2 mm to produce a diffraction pattern. Find the angular width of the central maximum obtained on the screen.
Estimate the number of fringes obtained in Young’s double slit experiment with fringe width 0.5 mm, which can be accommodated within the region of total angular spread of the central maximum due to single slit. (the wavelength of the light is given in mm but all the calculations are done using it as nm)
A. Unpolarized light is a beam of light where the vibration of light vectors are in all directions in the plane which is perpendicular to direction of propagation of light whereas in linearly polarized light the vibration of light vectors is only in one direction in a plane which is also perpendicular to the direction of motion.
Polarized light can be distinguished from unpolarized light by using a polaroid. When a linearly polarized light is passed through a polaroid, it will only pass through the polaroid if the pass axis of polaroid is parallel to the light vector and there will be no change in the intensity when the polaroid is rotated.
Linearly polarized light can be obtained by a polarizer, the electric field vectors which are not parallel to the aligned molecules of the polarizer get absorbed and which are parallel are not absorbed thus a linearly polarized light is obtained.
B. Given: -
The intensity of the incident light I0
Calculation: -
After passing the first polaroid P1 the intensity be I1
We know that I1 reduces to half After passing the third polaroid P2 the intensity be I2 We can write by malus’ law as,
Where, I0 is the intensity of incident light and 
= 60o is the angle between the pass axis of P1 and P2
So, the intensity of light passed through P2 is,
Conclusion: -
the intensity of light after passing through P2 is,
OR
A.
B. Given: -
Wavelength of light, λ = 500 nm
Width of the single slit, a = 0.2 mm
Distance between the double slits, d= 0.5 mm
Formula: -
In a diffraction obtained through single slit,
The angular width of the central maxima (ω) is given as,
And linear width of the central maxima (ω’) is given as,
In Young’s double slit experiment,
The fringe width (β) is defined as,
Where, λ is the wavelength of the light is used for diffraction/interference, and a is the width of the single slit, d and D is the distance between the slits, and sources and the screen respectively in young double slit experiment,
Calculations: -
Substituting the values given in the above formula we get,’
ω = 5 × 10-3 radians
Also, linear width is
Given that maximum fringes in young double slit expression that fit the same length is n,
Also, width of one fringe is,
So total length is, nβ, which gives,
nβ = ω’
So, n = 5
Conclusion: -
Hence, the angular width of the central maximum is, ω = 5 × 10-3 radians.
And the number of fringes obtained in young double slit experimaent, accommodated within the region of total angular spread of the central maximum due to single slit are n = 5.
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