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Question : 26
Total: 27
Explain, with the help of a diagram, how plane polarized light can be produced by scattering of light from the Sun.
Two polaroidsP 1 P 2 I P 1 P 3 P 1 P 2 45 ∘ P 1 P 1 , P 2 P 3
OR
(a) Why cannot the phenomenon of interference be observed by illuminating two pin holes with two sodium lamps?
(b) Two monochromatic waves having displacementsy 1 = a cos ω t y 2 = a cos ( ω t + f )
(c) Two wavelengths of sodium light of590 nm 596 nm 2 × 10 − 6 m 1.5 m
Two polaroids
OR
(a) Why cannot the phenomenon of interference be observed by illuminating two pin holes with two sodium lamps?
(b) Two monochromatic waves having displacements
(c) Two wavelengths of sodium light of
Solution:
ns. Diagram production of polarized light by scattering of sun light
● Explanation
● Calculation of intensity of light transmitted throughP 1 , P 2 P 3
Diagram :
Alternatively: If the student writes " scattered light when viewed in a perpendicular direction is found to be polarised
(Award one mark) Intensity of light transmitted by1 st
I 1 =
Intensity of light transmitted by2 nd
I 2 = I 1 cos 2 45 ∘ =
(
) 2 =
Intensity of light transmitted by3 rd
I 3 = I 1 cos 2 45 ∘ =
(
) 2 =
OR
● Reason
● Deriving the expression for resultant intensity and condition for constructive and destructive interference
● Calculating the separation
(a) Because two independent sources cannot be coherent OR they are not coherent
(b)y 1 = a cos ω t
y 2 = a cos ( ω t + ϕ )
So resultant displacement is give by
y = y 1 + y 2
y = a cos ω t + a cos ( ω t + ϕ )
y = 2 a cos ( ϕ ∕ 2 ) cos ( ω t + ϕ ∕ 2 )
The amplitude of the resultant displacement is2 π cos ( ϕ ∕ 2 ) I = 4 I 0 cos 2 ( ϕ ∕ 2 )
For constructive interference:
ϕ = 0 , ± 2 π , ± 4 π , . . . . . . .
For destructive interference:
ϕ = 0 , ± π , ± 3 π , ± 5 π , . . . . . . .
(c) Position of second maxima,
y 2 =
Separation between the positions of the second maxima withλ 1 λ 2
∆ y =
=
= 11.25 × 10 − 3 m
● Explanation
● Calculation of intensity of light transmitted through
Diagram :
Explanation: Charges accelerating parallel to the double arrows do not radiate energy towards the observer. The radiation scattered by the molecules therefore is polarised perpendicular to the plane of the figure.
Alternatively: If the student writes " scattered light when viewed in a perpendicular direction is found to be polarised
(Award one mark) Intensity of light transmitted by
Intensity of light transmitted by
Intensity of light transmitted by
OR
● Reason
● Deriving the expression for resultant intensity and condition for constructive and destructive interference
● Calculating the separation
(a) Because two independent sources cannot be coherent OR they are not coherent
(b)
So resultant displacement is give by
The amplitude of the resultant displacement is
For constructive interference:
For destructive interference:
(c) Position of second maxima,
Separation between the positions of the second maxima with
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