Rays of light are coming from lamp and are incident perpendicular to tourmaline plate. If plate is rotated keeping incident ray as an axis, intensity of light found
(A) constant
(C) maximum
(B) zero
(D) varying
Answers
Explanation:
Key Concept According to law of Malus, when a beam of completely plane polarised light is incident on an analyser, the resultant intensity of light (l) transmitted from an analyser varies directly as the square of cosine angle between plane of analyser and polariser.
Let initial intensity is I and final intensity is I
′
,
then
I
′
=Icos
2
60
=I(
2
1
)
2
=
4
I
Now, % difference between initial and final intensities,
=
I
I−
4
I
×100=
4
3I
×
r
1
×100
=
4
3
×100=75%.
Answer:
The correct optn is (B) zero, as the intensity of the transmitted light will be zero when the plate is rotated to certain angles. However, if the plate is rotated to a position where both polarisations of light are transmitted equally, the intensity of the transmitted light will be maximum. So the intensity of light varies with the rotation of the tourmaline plate.
Explanation:
When light is incident ⊥ on a tourmaline plate, the intensity of the transmitted light will depend on the orientation of the plate.
Tourmaline is a naturally occurring mineral that has the property of double refraction, which means that it splits the incident light into two polarized beams.
One of these beams is transmitted with a velocity that depends on the orientation of the plate, while the other beam is reflected.
When the tourmaline plate is rotated around the incident ray, the orientation of the plate changes, and so does the velocity of the transmitted beam.
At certain angles of rotation, the plate will transmit only one polarisation of light, and the intensity of the transmitted light will be maximum.
At other angles of rotation, the plate will transmit only the other polarisation of light, and the intensity of the transmitted light will be zero.
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