SATHEE: wave-optics Question 39

wave-optics Question 39

Question: Q. 5. Figure shows a system of two polarizing sheets in the path of initially unpolarized light. The polarizing direction of first sheet is parallel to $x$ -axis and that of second sheet is $60^{\circ}$ clockwise from $x$ -axis. Calculate what fraction of intensity of light emerges from the system.

R [SQP 2016]

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Solution:

Ans.

[CBSE Marking Scheme, 2016]

Detailed Answer :

As the axis of first polaroid is parallel to $x$ -axis all the light passes through it polarised and passes the second polaroid is at an angle $60^{\circ}$ with the incident light.

$∴$ By Malus’ law

$\begin{aligned} I_{2} & = I_{1} \cos^{2} ϕ & = \frac{1}{2} I_{0} \cos^{2} 60^{\circ} & = \frac{1}{2} \times \frac{I_{0}}{4} = \frac{I_{0}}{8} \end{aligned}$

[A] Q. 6. Find an expression for intensity of transmitted light when a polaroid sheet is rotated between two crossed polaroids. In which position of the polaroid sheet will the transmitted intensity be maximum?

R [Delhi I, II, III 2015]

Ans. Let the rotating polaroid sheet makes an angle $θ$ with the first polaroid.

$∴$ Angle with the other polaroid will be $(90 - θ) 1$

Applying Malus’ law between $P_{1}$ and $P_{3}$

Between $P_{3}$ and $P_{2}$

$\begin{aligned} I_{2} = I_{3} \cos^{2} (\frac{π}{2} - θ) & I_{2} = (I_{1} \cos^{2} θ) \cos^{2} (\frac{π}{2} - θ) \end{aligned}$

$\Rightarrow I_{2} = \frac{I_{1}}{4} \sin^{2} 2 θ = \frac{I_{0}}{8} \sin^{2} 2 θ \frac{1}{2}$

$∴$ Transmitted intensity will be maximum when

$θ = \frac{π}{4}$

$1 / 2$

[CBSE Marking Scheme 2015]

[Topper’s Answer, 2015]

Short Answer Type Questions-II

(3 marks each)

Wave Optics

wave-optics Question 39

Detailed Answer :

Short Answer Type Questions-II

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Wave Optics

wave-optics Question 39

Detailed Answer :

Short Answer Type Questions-II

Table of Contents

Engineering Preparation

Medical Preparation

NCERT Books & Solutions

Important Resources

Other Resources

Syllabus

Test Platform

Sample Mock Test

Mentorship

NCERT Exercise Video Solution

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