UNIT- 3: Polarization and Lasers

Q.1 In a uniaxial crystal, the number of directions along which the two refracted rays travel with

A Same velocity is one

B Same velocities are two

C Same velocities are three

D None of these

Ans A: Same velocity is one

Q.2 What principle is responsible for the fact that certain sunglasses can reduce glare from reflected

surfaces?

A Refraction

B Polarization

C Reflection

D Diffraction

Ans B: Polarization

Q.3 Plane polarization light can be produced by

A Nicol prism

B Pile of Plates

C All of above

Ans C

Q.4 When a ray of unpolarized light is a direction parallel to the optic axis of a calcite, o and e-rays travel

A Along the different direction with the same velocity

B Along the direction with same velocity

C Along the same direction with different velocity

D Along the different directions with different velocities

Ans B: Along the direction with same velocity

Q.5 When a ray of unpolarized light is passed through a uniaxial negative crystal it is split up into two

reflected rays the relation between the velocities of e and o rays are

A VO ˃Ve

B Ve ˃Vo

C Ve =Vo

D Ve ˃Vo

Ans B

Q.6 The velocity of o-ray and e-ray in a crystal is same along the direction of A Optic Axis

B Geometrical axis

C none

Ans A

Q.7 In a nicol prism, the O-ray is totally internally reflected but E-ray is transmitted. The statement is

A True

B False

C Partially true

Ans A

Q.8 When an unpolarized ray fall on a Nicol prism, the emergent ray from it is

A Plane polarized E-ray

B Plane polarized o-ray

C Circularly polarized E-ray

Ans A

Q.9 If the intensity of the light under test changes and varnishes, due to passage through the rotating Nicol

prism, the light is

A Plane polarized

B Circularly polarized

C Unpolarized

Ans A

Q.10 If the angle between the optic axis and the vibration of plate polarized light is other than 00, 450, and 900 , then the emergent beam from quarter-wave plate is

A Plane polarized

B Elliptically polarized

C Circularly polarized

Ans B

Q.11 The phenomenon by which the plane of variation of a polarizing light passing through quartz is rotated

through a certain angle but the types of polarizing remain the same, is called

A Optical resistivity

B Photometry

C Optical activity (or optical rotation)

Ans C

Q.12 The disadvantages of a quarter-wave plate or half-wave plate is that A They produce variable path difference between O-ray and E-ray B They produce constant path difference between O-ray and E-ray C They produce variable phase difference between O-ray and E-ray

Ans B

Q.13 Unpolarized light falls on two Nicols so oriented that no light is transmitted if a third nicol placed

between them not either of the two nicols in question then

A No light is transmitted

B Some light is transmitted

C Light may or not be transmitted

D Exactly 50% light is transmitted

Ans B: Some light is transmitted

Q.14 When a plane polarized light passed through a half wave plate the emergent light is

A Elliptically polarized

A Plane polarized

B Unpolarized

B Plane polarized

C A mixture of elliptically and circularly polarized

D Circularly polarized

Ans B: Plane polarized

Q.15 Circularly polarized light is produced if the amplitudes of the ordinary and extra ordinary rays are equal

and there is a phase difference of

A П

B П/2

C П/4

D Zero

Ans B

Q.16 When elliptically polarized light after passing through quarter wave plate is observed through a rotating

nicol the emergent light would have shown

A The variation of intensity with minimum not zero

B No variation in intensity

C The variation of intensity with minimum zero

D The intensity of the emergent light is same

Ans C: The variation of intensity with minimum zero

Q.17 When light is incident at Brewster angle

A The refracted light is plane polarized

B The reflected light is partially plane polarized

C The reflected light is circularly polarized

D The refracted light is plane polarized

Ans D: The refracted light is plane polarized

Q.18 On rotating the analyser the intensity ,of emergent light varies between a maximum and minimum

which with zero ,then light incident on the analyzer.

C Partially plane polarized

D Circularized polarized.

Ans Plane polarized

Explanation This is the characteristics of ppl for detection.

Q.19 On rotating the analyzer the intensity of emergent light varies between a maximum and minimum

which is not zero, then light incident on the analyzer.

A Plane polarized

B Unpolarized

C Partially plane polarized

D Circularly polarized

Ans C: Partially plane polarized

Q.20 On rotating the analyzer the intensity of emergent light does not vary then the light I ncident on the

analyser is

A Either plane polarized or partially polarized

B Either unpolarized or circularly polarized

C Either partially polarized or elliptically polarized

D Only circularly polarized

Ans B: Either unpolarized or circularly polarized

Q.21 If on rotating the analyzer the intensity of the emergent light varies between a maximum and minimum

but does not fall to zero then the light incident on the analyzer is

A Circularly polarized

B Plane polarized

C Unpolarized

D Elliptically polarized

Ans D: Elliptically polarized

Q.22 An Unpolarized beam of intensity Io is incident on two analyzers placed together if Ɵ is the angle

between the axes of the two analyzers then the intensity of light transmitted through both analyzer is

A Io

B Iocos2Ɵ

C ½ cos2Ɵ

D Zero

Ans B

Q.23 Plane polarized light is incident or an analyzer if the intensity of the emergent ray falls to three fourth

the angle of the axis of the analyzer with respect to the plane of vibration if incident polarized beam is

A 30

B 45

C 60

D 0

Ans A: 30

Q.24 To analyze a plane polarized lights an analyzer is rotated in one complete rotation of the analyze the

following phenomenon occurs

A One complete extinction

B One brightness and one time total darkness

C Two time brightness and one time total darkness

D Two time brightness and two time total darkness

Ans D: Two times brightness and two times total darkness

Explanation Alternate maxima or minima will appear for each 90 rotation of the analyzer

Q.25 An unpolarized beam of intensity 2a2 passes through a polaroid the intensity of emergent plane

polarized light is

A A2

B 2a2

C 2 a2

D A2/2

Ans: A: A2

Explanation by using the property polarized

Q.26 In a doubly refracting along optic axis

A µo>µe

B µo=µe

C µo<µe

D µo=µe2

Ans: B

Q.27 The axis of two nicol prisms are parallel to one another one of the two nicols is rotated through an angle

of 60 the ratio of the intensity of transmitted light before and after rotation is

A 1:2

B 2:1

C 4:1

D 1:4

Ans: C: 4:1

Q.28 Two plane polarized beams of equal amplitudes having a phase difference aremutually

perpendicular the superposition of these two beams results is

A Plane polarized

B Circularly polarized

C Elliptically polarized

D Partially plane polarized

Ans: B: Circularly polarized

Explanation: this is the condition of producing by superposing two sine wave

Q.29 Polarized light can produced by

A Reflection

B Refraction

C Double refraction

D All of them

Ans: D: All of them

Explanation: using the property of double refracting crystal

Q.30 Brewster s law in terms of refractive index can be expressed as

A µ=sin IP

B µ= cos IP

C µ=tan IP

D µ=cot IP

Ans: C

Explanation definition of law

Q.31 According to Malus law the intensity of polarized light emerging through the analyzer varies as

A I0 cos 2Ɵ

B I0 sin2Ɵ

C I0 cos Ɵ

D I0 /2 cos 2Ɵ

Ans: A

Q.32 Polarization cannot occur in

A Light waves

B x-rays

C Radio waves

D Sound waves

Ans: D: Sound waves

Explanation Polarization is the property of transverse wave sound is a longitudinal wave

Q.33 Which of the following statements indicate that the light waves are transverse

A Light waves can travel in vacuum

B Light waves show interference

C Light waves can be polarized

D Light waves can be diffracted

Ans: C: Light waves can be polarized

Q.34 Biaxial crystal among the following is

A Quartz

B Calcite

C Tourmaline

D Selenite

Ans D: selenite

Explanation by definition

Q.35 Ordinary light incident on a glass slab at the polarizing angle is refracted in glass and suffers a deviation

of 22 the value of the angel of refraction in glass in this case is

A 68

B 56

C 21

D 34

Ans B:56

Q.36 When unpolarized light enters a double refracting crystal we get two refracted rays called ordinary ray

(o-ray) and extraordinary rays (e-ray) which of the following statement is true

A Only o-ray polarized

B Only e-ray polarized

C Both o and e-ray are polarized

D Neither o-ray nor e- ray is polarized

Ans C: Both o and e-ray are polarized

Explanation properties of double refracting crystal

Q.37 Unpolarized light can be converted into a partially polarized or plane polarized by several processes

which of the following does do that

A Reflection

B Diffraction

C Double Refraction

D Scattering

Ans B: Diffraction

Explanation In case of diffraction there is no change in the property of light

Q.38 Which one is the example of biaxial crystal

A Sodium

B Tourmaline

C Quartz

D Aragonite

Ans D: aragonite

Explanation By definition

Q.39 The superposition at two plane polarized lights in two mutually perpendicular directions given by

x=4sin ( t y=5sin( t will result in

A Plane polarized light

B Unpolarized light

C Elliptically polarized light

D circularly polarized light

Ans C: Elliptically polarized light

Explanation unequal amplitudes produce elliptically polarized light

Q.40 Two polarizing sheets have two polarizing directions parallel so that intensity of the transmitted light is

maximum if the intensity is so to drop by one half then either of the two sheets must be turned by

A +30 and +135

B +45 and +120

C +30 and +120

D +45 and +135

Ans D: +45 and +135

Q.41 If t is the minimum thickness of a quarter wave plate needed to convert unpolarized light of wavelength

480 nm to circularly polarized light then the corresponding thickness of a quarter wave plate the

wavelength 600 nm is

A 0.50t

B 0.75t

C 1.25t

D 1.44t

Ans C: 1.25t

Q.42 The thickness of a quarter wave plate made of quartz for wavelength 5000 a refractive index e=1.553

and o =1.543 is

A 500 × 10-3

cm

B 3.75 × 10-3

cm

C 7.50 × 10-3

cm

D 1.25 × 10-3

cm

Ans. D

Unit 3: Subtopic: Lasers

Q.43 In a spontaneous emission an electron from excited level makes transition to the ground level when

A Hit by photon of energy equal to the energy gap

B By its own

C Hit by photon of energy equal more than the energy gap

D By electric filed

Ans B: By its own

Q.44 In a stimulated emission an electron from excited level makes transition to the ground level when

A Hit by photon of energy equal to the energy gap

B By its own

C Hit by photon of energy equal more than the energy gap

D By electric filed

Ans A: Hit by photon of energy equal to the energy gap

Q.45 The population inversion is defined as the

A Moving maximum electrons of the surfaces of active materials

B Decreasing population of electrons

C Increasing population of holes

D Making excited level more populated than ground level

Ans D: Making excited level more populated than ground level

Q.46 The material in which the population is achieved is called as

A Active medium

B Metastable state

C Passive medium

D Stable state

Ans A: Active medium

Q.47 The ruby laser is

A Continuous laser

B Gas laser

C Semiconductor laser

D Pulsed laser

Ans D: Pulsed laser

Q.48 The method used for achieving population inversion inversion in a He-Ne laser is

A Optical pumping

B Inelastic scattering

C Forward biasing

D Chemical reaction

Ans B: Inelastic scattering

Q.49 The method used for achieving population inversion in a ruby laser is

A Optical pumping

B Inelastic scattering

C Forward biasing

D Chemical reaction

Ans A: Optical pumping

Q.50 A semiconductor diode laser is level laser system

A Four level

B Three level

C Two level

D One level

Ans C: Two level

Q.51 In a semiconductor diode the doping concentration is so high that the Fermi level in n-type of diode

(laser) lies

A Centre of energy gap

B Top of valence

C Bottom of conduction band

D Inside the conduction band

Ans D: Inside the conduction band

Q.52 The coherence length of a laser light is

A 4000 a

B 8000 a

C 300 m

D 2 m

Ans 300 m

Q.53 A He-Ne laser is a level laser system

A One

B Two

C Three

D Four

Ans D: four

Q.54 The main properties which is used for engineering application of laser is

A Intensity and directionality

B Frequency

C Wavelength and Frequency

D Monochromacity

Ans A: Intensity and directionality

Q.55 An optical fibre cable acts on the principal of

A Double refraction

B Refraction

C Total external refraction

D Total internal refraction

Ans D: Total internal refraction

Q.56 A hologram records of light

A Intensity

B Frequency

C Intensity and phase

D Frequency and phase

Ans B: Frequency

Q.57 If a hologram is illuminated by white light it will from

A Colorful (rainbow) image

B Will not from image

C Single color image

D Red imaged in black and white

Ans A: Colourful (rainbow) image

Q.58 Laser beam is made of

A Electrons

B Highly coherent photons

C Very light and elastic particles

D None of them

Ans B: Highly coherent photons

Q.59 In population inversion

A The number of electrons in higher energy state is more than the ground state

B The number of electrons in lower energy state is more than higher energy state

C The number of electrons in higher and lower energy state are same

D None of them

Ans A: The number of electrons in higher energy state is more than the ground state

Q.60 The characteristics of laser beam are

A Highly directional

B Highly intense

C Highly monochromatic

D All of them

Ans D: All of them

Q.61 The energy of photon is equal to

A h v

B 2hv

C hv/2

D None of them

Ans A: hv

Q.62 Which event is likely to take place when a photon of energy equal to the difference in energy between

two levels is incident in a system

A Absorption

B Emission

C Absorption and emission

D None of the above

Ans C: Absorption and emission

Q.63 During the laser amplification total loss is not due to following reason

A Transition absorption and scattering by the emission

B Absorption within the medium

C Scattering due to the optical in homogeneity

D Energy loss

Ans D: Energy loss

Q.64 The physicist who first predicted that the atom can emit radiation by the process of stimulated emission

in addition to spontaneous emission was

A Newton

B Einstein

C Fresnel

D Townes

Ans B: Einstein

Q. 65 In He-Ne lasers, the ratio is in the order of

A 1:10

B 1:1

C 100:1

D 6:1

Ans. D

Explanation This is standard ratio

Q. 66 A three level laser system will be

A Always continuous wave (cw)

B Either continuous or pulsed

C Always pulsed

D Made continuous as well as pulsed by temperature control

Ans. C

Explanation Example of Ruby Laser

Q. 67 In Ruby Lasing material the percentage of chromium in aluminum oxide is

A 0.5

B 0.05

C 5

D 0.005

Ans. B

Explanation This is standard percentage

Q. 68 The colour of laser output from ruby laser is

A Green

B Violet

C Blue

D Red

Ans. D

Explanation Characteristics of lasers

Q. 69 In He-Ne lasers, the ratio of He-Ne is in the order of

A 1:10

B 1:1

C 100:1

D 6:1

Ans. D

Explanation standard ratio

Q. 70 The wavelength of emission from He-Ne is

A 10.64 m

B 337.1nm

C 694.3nm

D 632.8 nm

Ans. D

Explanation standard wavelength of He-Ne laser

Q. 71 An optical fibre cable acts of the principle of

A Double refraction

B Reflection

C Total external reflection

D Total internal reflection

Ans. D

Explanation Principle of optical fibre

Q. 72 If a hologram is illuminated by white light it will form

A Colorful (rainbow) image

B Will not form image

C Single colour image

D Red imaged in black and white

Ans. A

Explanation Hologram acts as diffraction grating

Q. 73 The energy of photon is equal to

A hν

B 2 hν

C hν/2

D None of them

Ans. A

Explanation Planck’s Relation

Q. 74 The type of pumping used in Ruby laser is

c Chemical pumping

B Electrical discharge

C In elastic atom-atom collision

D Optical pumping

Ans. Optical pumping

Explanation Pumping agent is Flash Xenon Tube

Q. 75 In ruby laser, the role of active centers is played by

A Al+3

ions

B Cr+3

C O-2

ions

D None of the above

Ans. B

Q. 76 The material in which the population is achieved is called as

A Active medium

B Metastable state

C Passive medium

D Stable state

Ans. A

Q. 77 Which of the following laser system is more efficient

A Two level laser system

B Three level laser system

C Four level laser system

D Both (C) and (D)

Ans. C

Explanation Proved by experimental evidences

Q. 78 Holography is invented by

A Denmis Gabor

B Einstien

C Newton

D Curie Brother

Ans. A

Q. 79 In reconstruction of images from hologram we get

A One real and virtual image

B Two real images

C Two virtual images

D Large number of real and virtual images

Ans. A

Q. 80 Propagation of light through fibre core is due to

A Diffraction

B Interference

C Total internal reflection

D Refraction

Ans. C

Q. 81 Information holding capacity of a hologram is

A Limited

B Large

C Less

D None of the above

Ans. B

Q. 82 Source of light in a fibre optic system

A LED and laser diode

B LED

C Laser Diode

D Photo diode

Ans. A

Explanation Because they are compact in size

Q. 83 The population inversion in He-Ne laser is produced by

A Chemical excitation

B Photon Excitation

C Chemical reactions

D Inelastic atomic collisions

Ans. D

Explanation Transfer of energy from He atom to Ne atom takes place through inelastic collision

Q. 84 At lower temperature Ruby laser produces the laser beam of wavelength

A 6328 Å

B 6943 Å

C 6934 Å

D 5896Å

Ans. C

Explanation At lower temperature ruby emits lower wavelength

Q. 85 What is the nature of output of 0.05 % Cr2O3 doped ruby laser

A Continuous

B Pulsed

C (a) And (b)

D Cannot defined

Ans. B

Explanation Characteristics of Ruby Laser

Q. 86 The reconstruction process in holography involves

A Interference phenomenon

B Diffraction

C (a) And (b)

D None of these

Ans. B

Explanation Light diffracts from hologram

Q. 87 Pumping source preferred for gaseous laser is

A Artificial pumping

B Electrical pumping

C Chemical pumping

D Thermal pumping

Ans. B

Explanation This is used for He-Ne laser

Q. 88 A laser light consists of:

A Cosmic rays

B Electrons stream

C Light material particles

D Perfectly coherent photons

Ans. D

Explanation All photons are in same phase, coherent source

Q. 89 Laser beam is highly coherent, so it can be used in

A Interference

B Diffraction

C Direct conversion

D Optical pumping

Ans. D

Q. 90 Ratio of probabilities of spontaneous emission and stimulated emission

A Independent of frequency ν

B Proportional to frequency ν

C Proportional νs

D Proportional ν2

Ans. C

Explanation As per Einstein coefficient

Q. 91 A lasing action works on the principle

A Electromagnetic theory

B Quantum theory

C None

Ans. B

Q. 92 In stimulated emission process the number of coherent photons are

A 2

B 1

C 3

Ans. A

Q. 93 The life time of metastable state in comparison to excited state is

A Smaller

B Greater

C Equal

Ans. B

Q. 94 In population inversion process the number of atoms in metastable state is comparison to the ground state is

A Smaller

B Greater

C Equal

Ans. B

Q. 95 Stimulated emission depends on

A The number of atoms present in the excited state

B The intensity of incident light

C Both

Ans. C

Q. 96 In thermal equilibrium during lasing action, the upward and downward transitions in between ground state and excited

is

A Equal

B Not equal

C None

Ans. A

Q. 97 In He-Ne laser 2 energy states of Ne are

A 1S,2S

B 1S,3S

C 2S,3S

Ans. C

Q. 98 The population inversion in preparing laser beam can be achieved

A when one of the excited states in more populated that the ground state

B when one of the excited state is less population then the ground state

C none

Ans. A

Q. 99 A beam of light is incident on a glass plate at an angle of incidence 600. The reflected ray is polarized. What is the

angle of refraction, if the angle incidence is 450.

A 60

B 30

C sin-1 (1/√6)

D sin-1 (1/√3)

Ans. C

Q. 100 The axes of two nicol prisms are parallel to one another. One of the two nicols is rotated through an angle of 600.

The ratio of the intensity of transmitted light before and after rotation is:

A 1:2

B 2:1

C 4:1

D 1:4

Ans. C