Engineering Physics Questions and Answers – Production of Plane Polarised Light

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This set of Engineering Physics Questions & Answers for Exams focuses on “Production of Plane Polarised Light”.

1. The direction of polarization of an electromagnetic wave is considered to be the direction of __________
a) Electric Field
b) Magnetic field
c) Resultant of Electric field and Magnetic Field
d) Perpendicular to both Electric and Magnetic Field

Explanation: The direction of polarization of an electromagnetic wave is taken as the direction of the electric field vector because many common electromagnetic wave detectors respond to the electric forces on electrons in material not magnetic forces.

2. The second polaroid placed after the ray has been polarized is called as __________
a) Polarizer
b) Analyzer
c) Brewster’s Window
d) Multi Polaroid

Explanation: The second polaroid is placed after the ray has already been polarized to analyze whether the ray is polarized completely or not. Thus, it is called the polarizer.

3. An unpolarized light can be polarized by __________
a) Reflection
b) Refraction
c) Diffraction
d) Interference

Explanation: An unpolarized light can be polarized by reflection. The extent of polarization depends on the angle of incidence. The reflected light is completely polarized for a specific angle, called the polarizing angle.
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4. Which of the following is a uniaxial crystal?
a) Borax
b) Mica
c) Quartz
d) Selenite

Explanation: Uniaxial crystals are those in which there is only one optic axis. Calcite, quartz, ice are a few examples. Borax, mica, and selenite are biaxial crystals which have two optic axes.

5. For a glass surface, the value of polarizing angle is _________
a) 45.7°
b) 52.7°
c) 57.5°
d) 67.8°

Explanation: Polarizing angle is the angle for which the reflected light would be completely plane polarized. For glass, it is 57.5°. Thus, if a light is incident on glass at 57.5° the reflected light would be completely polarized.

6. The refractive index of a material is 1.75. What is the polarizing angle?
a) 47.23°
b) 51.02°
c) 53.74°
d) 60.25°

Explanation: Using Brewster’s Law, Angle of incidence = tan-1μ
= tan-11.752
= 60.25.

7. A polarized light of Intensity 40 Wm2 is incident on the analyzer at a certain angle. If the transmitted beam has an Intensity of 20 Wm2, the angle made with the vertical is _____________
a) 30°
b) 45°
c) 60°
d) 75°

Explanation: Here, Io = 40 Wm-2, I = 20 Wm-2
Using Malus law, I = Iocos2θ
20 = 40 X cos2θ
cos2θ = 12
θ = 45°.

8. What angle should the beam made with the vertical, so that after passing through the analyzer, it’s intensity should become 0.86 times the initial intensity?
a) 30°
b) 45°
c) 60°
d) 75°

Explanation: Here, I = 0.86 Io
Using Malus law, I = Iocos2θ
0.86 Io = Io X cos2θ
cos2θ = 0.86
θ = 60°.

9. The sunlight as received by the observer is __________
a) Unpolarized
b) Partially Polarized
c) Polarized
d) Varying Polarizability

Explanation: The incident sunlight, when enters the earth’s atmosphere, is scattered by the particles present in the earth’s atmosphere. Due to this, the sunlight gets polarized.

10. If ray R1 is incident at the polarizing angle, which of the following rays are unpolarized?

a) R1
b) R2
c) Both R2 and R3
d) Both R1 and R3

Explanation: The incident ray is incident at an angle 57.5° which is the polarizing angle of the glass. Thus the reflected light is completely plane polarized, while the other two are not.

11. At the angle of polarization, p, the angle between the reflected and the refracted beam is __________
a) p
b) π
c) π /2
d) p/2

Explanation: If the angle of incidence is equal to p, the angle made by the refracted beam with the x-axis would be π /2 – p. The refracted beam would make an angle p with the x-axis. Thus, the angle between the two rays would be π /2.

12. Which of the two rays are polarized?

a) X
b) Y
c) Both X and Y
d) Neither X and Y

Explanation: The incident sunlight is unpolarized. On encountering the molecules of earth’s atmosphere, it changes its direction. Due to the scattering of light, the incident sunlight gets polarized.

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