Find an Expression for Intensity of Transmitted Light When a Polaroid Sheet is Rotated Between Two Crossed Polaroids. - Physics


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?



Let us consider two crossed polarisers P1 and P2, with a polaroid sheet P3 placed between them.

Let I0 be the intensity of polarised light after passing through the first polariser P1. If θ is the angle between the axes of P1 and P3, then the intensity of the polarised light after passing through P3 will be I=I0cos2θ.

As P1 and P2 are crossed, the angle between the axes of P1 and P2 = 90°.

∴ Angle between the axes of P2 and  P3 = (90°θ)

The intensity of light emerging from P2 will be given by






 The intensity of polarised light transmitted from P2 will be maximum when





Also, the maximum transmitted intensity will be given by


Concept: Polarisation
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2014-2015 (March) Delhi Set 2


If the polarising angle for a given medium is 60°, then the refractive index of the medium is.................

What is a Polaroid?

With the help of neat diagram, explain how non-polar dielectric material is polarised in external electric field of increasing intensity. Define polarisation in dielectrics.

Draw a neat labelled diagram showing the plane of vibration and plane of polarisation for polarised light.

For a glass plate as a polariser with refractive index 1.633, calculate the angle of incidence at which light is polarised.

If the critical angle of a medium is sin-1(3/5), find the polarising angle.

Why does an unpolarised light incident on a polaroid get linearly polarised ?

A beam of unpolarised light is incident on a glass-air interface. Show, using a suitable ray diagram, that light reflected from the interface is totally polarised, when μ = tan iB, where μ is the refractive index of glass with respect to air and iB is the Brewster's angle.

Show, via a suitable diagram, how unpolarised light can be polarised by reflection.

The refractive indices of glass and water w.r.t. air are 3/2 and 4/3 respectively. Determine the refractive index of glass w.r.t. water.

What is the Brewster angle for air to glass transition? (Refractive index of glass = 1.5)

The refractive indices of water for red and violet colours are 1.325 and 1.334 respectively.
Find the difference between the velocities of rays for these two colours in water. (c = 3 × 108 m/s)

A ray of light passes from a vacuum to a medium of refractive index (μ). The angle of
incidence is found to be twice the angle of refraction. The angle of incidence is _______.

A) `cos^(-1)(mu/2)`

B) cos−1(μ)

C)  `2 cos^(-1) (mu/2)`

D) `2 sin^(-1) (mu/2)`

Unpolarised light is passed through a polaroid P1. When this polarised beam passes through another polaroid P2 and if the pass axis of P2 makes angle θ with the pass axis of P1, then write the expression for the polarised beam passing through P2. Draw a plot showing the variation of intensity when θ varies from 0 to 2π.

What is the value of refractive index of a medium of polarising angle 60°?

State two uses of Polaroid.

The glass plate of refractive index 1.732 is to be used as a polarizer, its polarising angle is _______.

With the help of an experiment, state how will you identify whether a given beam of light is polarised or unpolarized?

State any two methods by which ordinary light can be polarised

Unpolarised light is incident on a polaroid. How would the intensity of transmitted light change when the polaroid is rotated?

Which of the following properties shows that light is a transverse wave?

A beam of light is incident at the polarizing angle of 35° on a certain glass plate. The refractive index of the glass plate is : 

Green light is incident at the polarising angle on a certain transparent medium. The angle of refraction is 30° . Find
(i) polarising angle, and
(ii) refractive index of the medium.

A ray of light is incident on a transparent medium at a polarizing angle. What is the angle between the reflected ray and the refracted ray?

What is the difference between polarised light and unpolarised light? 

A ray of ordinary light is travelling in air. It is incident on air glass pair at a polarising angle of 56°. Find the angle of refraction in glass.

Greenlight is an incident at the polarising angle on a certain transparent medium. The angle of refraction is 30°.
(i) polarising angle, and
(ii) refractive index of the medium.

The transverse nature of light is shown in ______.

Discuss polarisation by selective absorption.

What is a analyser?

What is unpolarised light?

State and obtain Malus’ law.

List the uses of polaroids.

State Brewster’s law.

What is the angle of polarisation and obtain the equation for an angle of polarisation?

Discuss about pile of plates.

What is double refraction?

Discuss about Nicol prism.

How is polarisation of light obtained by scattering of light?

What is normal focusing?

An unpolarised light of intensity 32 Wm-2 passes through three Polaroids such that the axes of the first and the last Polaroids are at 90°. What is the angle between the axes of the first and middle Polaroids so that the emerging light has an intensity of only 3 Wm-2?

The reflected light is found to be plane polarised when an unpolarized light falls on a denser medium at 60° with the normal. Find the angle of refraction and critical angle of incidence for total internal reflection in the denser to rarer medium reflection.

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Which of the following phenomena is not common to sound and light waves?

Figure shown a two slit arrangement with a source which emits unpolarised light. P is a polariser with axis whose direction is not given. If I0 is the intensity of the principal maxima when no polariser is present, calculate in the present case, the intensity of the principal maxima as well as of the first minima.

An unpolarized light beam is incident on the polarizer of a polarization experiment and the intensity of light beam emerging from the analyzer is measured as 100 Lumens. Now, if the analyzer is rotated around the horizontal axis (direction of light) by 30° in clockwise direction, the intensity of emerging light will be ______ Lumens.

A polarizer - analyser set is adjusted such that the intensity of light coming out of the analyser is just 10% of the original intensity. Assuming that the polarizer - analyser set does not absorb any light, the angle by which the analyser need to be rotated further to reduce the output intensity to be zero, is ______.


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