## NOUN TMA Questions and Answer: PHY406- Optics III

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### NOUN TMA Questions and Answer: PHY406- Optics III

NOUN TMA Questions and Answer: PHY406- Optics III

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Q1 If laser action occurs by the transition from an excited state to the ground state and it produces light of 693nm wavelength, what is the energy of the excited state. Take the energy of the ground state to be
zero.

12.77 eV

Q2 In seiconductor lasers pumping by direct conversion can be achieved with _______

light emitting diode

Q3 Which of the following is not a common mechanism of achieving population inversion?

cavity resonance

Q4 Which of these is correct about an atomic system at thermal equilibrium?

$$N_{1}> N_{2}$$

Q5 For lasers built as laser as laser oscillators, feedback mechinism for sustained oscillation is provided in the form of _______

resonant ca vity

Q6 Lasers built as laser amplifiers do not need

optical ca vity

Q7 Which of the following is not a prerequisite for the operation of laser?

spontaneous em ission

Q8 Media capable of producing light are known as _______ media

active

Q9 Which of the following correctly gives Planck's radiation law? The symbols have their usual meaning.

$$u(\nu)=\frac{8\pi{h}\nu}{c^3}\frac{1}{e^{h\nu/kT}-1}$$

Q10 Which of the following is correct when an atomic system is in thermal equilibrium at temperature T for stimulated emission to dominate spontaneous emission? Symbols have their usual meaning.

$$h\nu < < kT$$

Q11 Which of the following correctly gives the ratio of of the probability of spontaneous emission to the probabilty of stimulated emission? The symbols have usual meaning.

$$u(\nu)=\frac{8\pi{h}\nu}{c^3}$$

Q12 The basic condition for stimulated emission to occur in an excited atomic system is

population inversion

Q13 The theoretical basis for stimulated emission of radiation was put forward by

Einstein

Q14 Which of the following is INCORRECT about optical fibres?

core diameter lies between 100 t0 150 micrometre

Q15 In recording of the hologram with a laser ; microscope lenses broaden the sp;lit beams without affecting their ______________

coherence

Q16 In the off-axis hologram, the reference beam and the object beam arrive at the recording plate

from substantially different directions .

Q17 Momochromatic light waves have

single frequency

Q18 Which of the following atomic models explains the process of emission and absorption of light by atoms of heated solids, liquids or gases?

Bohr's

Q19 Which of the following devices is a source of light with high degree of coherence?

laser

Q20 In a Michelson interferometer experiment, a source producing a doublet of vacuum wavelength, $$\lambda_{1}$$ and $$\lambda_{2}$$ was used to illuminate the interferometer. If a displacement $$\Delta{d}$$ of one of the mirrors causes a one-cycle variation in the visibility (i.e. fringes disappear and re-appear), which of the following correctly gives the expression for $$\Delta{d}$$ in terms of $$\Delta\lambda\equiv {\lambda_{1}-\lambda_{2}}, \lambda_{1} and \lambda_{2} ?$$\frac{\lambda_{1}\lambda_{2}}{2\Delta{\lambda}}

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### Re: NOUN TMA Questions and Answer: PHY406- Optics III

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Q21 If the core and cladding refractive indices for a step-index fibre is 1.47 and 1.46 respectively, what will be the broadening of a pulse after a distance of 5 km?

$$0.17\mu{s}$$

Q22 Pulse dispersion in optical fibres arises from the following EXCEPT

the fact that kight pulse cannot travel into the cladding material at all

Q23 Optical communication carried out through open space compared to that through the optical fibre is not attractive because while light travels in open space between the information source and information use

is easily attenuated

Q24 A repeater essentially does the following to the signal EXCEPT

resonates

Q25 Optical communication refers to the transmission of the following information by light EXCEPT

speech
data
pictu re
---none of the above

Q26 The advantage of optical fibre over electrical conductors in communication includethe following EXCEPT

not secure to interceptions

Q27 A natural phenomenon which results due to the atmospheric gradient of refractive index is the

mirage

Q28 In optical communication, signal is transmitted through the fibre in the form of

pulses

Q29 Qptical fibre consists of a glass core and a cladding (also of glass) of lower refractive index. This type of fibre in which there is a sudden change in the refractive index at the core-cladding interface is called

step-index fi bre

Q30 In the figure shown, $$i_{max}$$ is referred to as the

light gathering capacity of the fibre

Q31 In the figure shown, the core is made of glass with refractive index 1.62 and is cladded with glass of refractive index 1.49. Calculate$$i_{max}$$

39.48 degrees

Q32 In the figure shown, the core is made of glass with refractive index 1.62 and is cladded with glass of refractive index 1.49. Calculate $$\phi$$

23.1 degrees

Q33 The core of an optical fibre made of glass with refractive index 1.62 is clad with glass of refractive index 1.49. Calculate the critical angle for the light travelling from the core to the cladding

66.9 degrees

Q34 Which of the following is INCORRECT about optical fibres?

core diameter lies between 100 t0 150 micrometre

Q35 Which is correct?

An optical fibre con sists of a cylindrical glass core surrounded by a transparent cladding of lower refractive index.

Q36 In communication, optical fibre is basically

a wave guid e

Q37 The advantage communication at optical frequencies has over communication at radio wave and microwave frequencies is that

increase in the frequency of the carrier wave enables it to carry more information

Q38 The property of fibre optics that makes it suitable for medical application is its ability to

cause light to travel through curved paths

Q39 Application of fibre optics depends primarily on the phenomenon of ________

total internal re flection

Q40 Which of the following wave properties of light wave is important in fibre optics?

refraction

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### Re: NOUN TMA Questions and Answer: PHY406- Optics III

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Q41 In order to obtain a hologram, the photographic plate on which the hologram is to be obtained

must be of high r esolution

Q42 Which of the following is NOT an application of holography

information storage
pattern recognition
microscopy
---none of the above

Q43 Which of the following is INCORRECT about photography?

A negative is obtained in both ordinary photography and holograp hy

Q44 If the angle subtended at the hologram by the signal and the reference beam is 15°, what is the spacing of the fringes provided the wavelength is 492 nm?

$$1.8 \mu{m}$$

Q45 Following Gabor, assume that amplitudes of signals and reference are in ratio 1:10. Suppose that the two beams when they combine may be completely out of phase or in phase. What is the maximum ratio of their intensities?

0.67

Q46 Which of the following is INCORRECT about photography?

In both ordinary photography and hologra phy, coherent source of light is used

Q47 In a beam of coherent laser light, all point on its wavefron are

in the same phase of vibration

Q48 In the off-axis hologram, the reference beam and the object beam arrive at the recording plate

from substantially different directions

Q49 In the production of a hologram, a hologram produced by the interference of a signal and reference wave which travel in the same direction is referred to as __________ hologram

in-line

Q50 In recording of the hologram with a laser ; microscope lenses broaden the sp;lit beams without affecting their ______________

coherence

Q51 In the off-axis hologram, the reference beam and the object beam arrive at the recording plate

from substantially different directions .

Q52 When two plane waves derived from a common source impinge at different angles on a screen, they produce a set of uniform, parallel interference fringes. The spacing of the fringes depends solely on the ___________ between the impinging waves

path difference

Q53 In holographib wave-front reconstruction, the phase relations are rendered visible to the photographic plate through the technique of _____________.

interferometry

Q54 In normal photography, photographic emulsion is, insensitive to ____________..

phase relations

Q55 To obtain a hologram, both the amplitude and the __________ of the wave must be recorded at each point on the recording surface.

Phase

Q56 Which of the following is correct iabout holography?

image formation requires lenses

Q57 The gabor zone pkate is similar to __________ zone plate

Fresnel

Q58 The light wave reflected from the object and received at the photosensitive surface at the time of recording the hologram is referred to as ___________

object wave

Q59 The light wave falling directly on the photosensitive plate is known as ________

reference wave

Q60 The technique of obtaining complete picture (as true as the object itself) of an object or a scene is known as _________

holography

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### Re: NOUN TMA Questions and Answer: PHY406- Optics III

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Q61 Calculate the coherence time if light of wavelength 660 nm has a wavetrain $$40\lambda$$ long.

$$8800\times{10^-17s}$$

Q62 Calculate the coherence length if light of wavelength 660 nm has a wavetrain $$40\lambda$$ long

26400 nm

Q63 In the experiment shown, as $$M_{2}$$ is moved further away from G, the circular interference fringes observed

Disappears

Q64 In the experiment shown, the glass plate marked $$G^{'}$$ acts as a _________

compensator

Q65 In the experiment shown, the glass plate marked G acts as a _________

beam split ter

Q66 The interval of time during which the phase of the wave motion changes in a predictable manner as it passes through a fixed point in space is referred to as

monochromaticit y

Q67 Light waves from ordinary sources have

frequency bandw idth

Q68 Momochromatic light waves have

single frequency

Q69 Which of the following is correct?

Transverse spatial coherence refers to the phase relationship between waves travelling side by side, at a certain distance from one another
Q70 If two light waves from coherent sources, with the same frequency, amplitude and phase difference of $$180^{o}$$ are superposed, then the resultant intensity is

Zero

Q71 If two light waves from coherent sources, with the same frequency, amplitude and phase are superposed, then the resultant intensity is

is four times any of the individual intens ities

Q72 Which of the fllowing is INCORRECT?

When light waves from two incoherent sources interfere, there will be interference fringe pattern o n the screen

Q73 When light waves from two incoherent sources interfere, the resultant intensity is

the sum of individual intensities and the screen will be uniformly illuminated

Q74 In the experiment shown, what determines whether the resultant intensity is a uniform illumination or a fringe pattern on the screen is the

interference term

Q75 In the experiment shown, the average intensity in the interference fringes observed is proportional to

the square of the time-averaged value of the superposed electric fields associated with light waves from A and B

Q76 In the experiment shown, a necessary condition for interference patterns to be seen on the screen that waves from A and B must

have constant phase relationship

Q77 Which of the following is NOT correct in the experiment shown?

dark fringes on the screen are the result of interference of light waves from $$S_{1}$$ and $$S_{2}$$ that are in phase

Q78 Which of the following is correct in the experiment shown?

The intensity of light is directly proportional to the time-average d square of the elelctric field intensity

Q79 Interaction of two or more waves arriving at a point to produce a wave of larger or smaller amplitude is referred to as _______

interference

Q80 Light waves from two slits tha have constant phase relationship are said to be

coherent

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