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Malus's Law - Practice Questions & MCQ
Edited By admin | Updated on Sep 18, 2023 18:34 AM | #JEE Main
Quick Facts
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Malus' Law is considered one of the most asked concept.
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12 Questions around this concept.
Solve by difficulty
Two beams, A and B, of plane-polarized light with mutually perpendicular planes of polarization are seen through a polaroid. From the position when beam A has maximum intensity (and beam B has zero intensity), a rotation of polaroid through 300 makes the two beams appear equally bright. If the initial intensities of the two beams are IA and IB respectively, then equal :
When an unpolarized light of intensity is incident on a polarizing sheet, the intensity of the light that does not get transmitted is
A plane polarized light is incident on a polariser with its pass axis making angle θ with x-axis, as shown in the figure. At four different values of θ, θ= ,
,
and
, the observed intensities are same. What is the angle between the direction of polarization and x-axis ?
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A beam of un-polarised light of intensity I0 is passed through a Polaroid A and then through another Polaroid B which is oriented so that its principal plane makes an angle of 450 relative to that of A. The intensity of the emergent light is :
Concepts Covered - 1
Malus' Law
Malus' Law-
This law states that the intensity of the polarized light transmitted through the analyzer varies as the square of the cosine of the angle between the plane of transmission of the analyzer and the plane of the polarizer.
As,
$
I=I_0 \cos ^2 \theta \text { and } A^2=A_0^2 \cos ^2 \theta \Rightarrow A=A_0 \cos \theta
$
If $\theta=0^{\circ}, I=I_0, A=A_0$, and if $\theta=90^{\circ}, I=0, A=0$
If $\mathrm{I}_{\mathrm{i}}=$ Intensity of unpolarised light. So
$
I_0=\frac{I_i}{2}
$
i.e. if an unpolarized light is converted into plane polarised light (say by passing it through a Polaroid or a Nicolprism), its intensity becomes half and
$
I=\frac{I_i}{2} \cos ^2 \theta
$
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