Lasers & Optical Fibers

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Dorothy Cole
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1 Lasers & Optical Fibers 1. Emmission of a poton by an excited atom due to interaction wit passing poton nearby is called A) Spontaneous emission B) Stimulated emission C) induced absorption D) termionic emission. 2. Te emission of poton witout being aided by any external agency is call A) ligt emission B)induced absorption C)stimulated emission D) spontaneous emission 3. Te life time of an atom at te ordinary excited state is of te order of A) a few millisecond B)few nano second C)few micro second D)Unlimited 4. Meta stable states are A) Ground state energy states B) excited energy levels in wic electrons stay for sort interval of time C) excited energy levels in wic electrons stay for unusually long time D)nuclear energy states. 5. If n 1 is te number density of lower energy E 1 and n 2 is te number of iger energy E 2, ten te condition n 2 >n 1 is referred to as A) tick population B)inverted population C)normal population D)no population. 6. Wic of te following is not te property of laser A) Higly monocromatic B) ig directionality C) very narrow line widt D) igly divergent 7. Supply of energy to atoms for excitation is called A) glowing B)bombarding C) incidenting D) pumping 8. Te required condition to acieve laser action in a system is A) State of population inversion B) excitation source C) a resonant cavity D)all te 3 9. Important caracteristic of laser beam is A) Interference B) diffraction C) dispersion D)Coerence 10. Spontaneous emission of ligt produces A) Coerent ligt B)incoerent ligt C)unidirectional ligt D)none of tese 11. Te expression for energy density in terms of Einstein s coefficients

2 A)U γ =B/A [1/e γ/kt -1] B) U γ =B/A [1/1-e γ/kt ] C) U γ =A/B [1/e γ/kt -1] D) U γ =A/B [1/e γ/kt +1] 12. In a laser, te mirrors are tere on eiter side of te device A) In order to filter te eat & leave out only ligt B) to protect eye of te observer C) to save energy of te excitation source D) so tat same potons continue to cause furter batces of stimulated transitions 13. Te wavelengt of emission of CO 2 laser is A) 632.8nm B) 10.6µm C) 1.064nm D) 694.3nm 14. Te population of te various energy levels of a system in termal equilibrium is given by A) Boltzmann distribution law B) Einstein relations C) planck s law D)Brewsters law 15. Te population ratio is given by A) N 2 /N 1 = e ΔE/kT B) N 2 /N 1 = e- ΔE/kT C) N 1 /N 2 = e ΔE/kT D) N 1 /N 2 = e- ΔE/kT 16. Multiplication of potons takes place in process A) Stimulated emission B) induced absorption C) Spontaneous emission D)none 17. CO 2 laser is invented by A) T.Maiman B)AliJawan C)Einstein D)C.K.N. Patel 18. Te CO 2 ratio of CO 2 : N 2 : He used in CO 2 laser is A) 5: 4 : 1 B) 4: 5 : 1 C) 1: 4 : 5 D) ) 1: 5 : Matematically spontaneous emission is represented as A) A * A+γ B) A A * +γ C)A+A * γ D)none 20. A medium in wic ligt gets amplified is known as A) Rarer medium B) denser medium C)active medium D)none 21. If te angle of incidence of a ray is equal to te critical angle at te interface of core and cladding, ten te ray travels A) In te cladding B) in te core C) along te interface D)in te buffer

3 22. In a single mode fiber, te diameter of te core is equal to A) 125µm B) 100 µm C) 50 µm D) 10 µm 23. Numerical aperture of an optical fiber depends on A) Diameter of te fiber B) acceptance angle C)critical angle D)n core material 24. Attenuation means A) Amplification of signal strengt B) division of signal C) loss of signal strengt D) modification 25. Te loss of power by te optical signal troug te optical fiber is called A) Rayleig scattering B)Raman scattering C) wein s scattering D)All of tese 26. Delay distortion occurs due to A) Irregularities in fiber structure B) variation in refractive index core at different points C) Spreading of pulses D) macroscopic bends 27. In a graded index fiber te refractive index of cladding varies A) Exponentially B) linearly C) parabolically D) None of tese 28. Te attenuation of optical fiber is expressed in A) om/km B) Watt/Km C) decibel/km D) joule/km 29. Te ion wic enters in to te fiber constitution at te time of fiber fabrication and causes absorption loss is A) Cl - B)SO 4 C) OH - D)Na Wen a ligt travels in a material medium its intensity decreases as te distance travelled increases. Tis is known as A)Snell s law B)Malus law C) Lambert s law D) Brewster s law 31. Acceptance angle of te fiber is expressed as A) θ 0 = sin -1 (N.A) B) θ 0 = sin -1 (n 1 /n 2 ) C)sin θ 0 =n 1.n 2 D) sin θ 0 =n 1./n If te optical fiber is kept in a medium of n instead of air, te acceptance angle A) increases B) decreases C) remains same D) all of tese 33. Fractional index cange of optical fiber and refractive index of core are and 1.533

4 respectively. Te cladding refractive index is A) B) C) D) V- number of te optical fiber A) Gives te exact no. of modes propagation troug te fiber B) is directly proportional to te number of modes propagating troug te fiber C) describes te different modes propagating troug te fiber D) Is meant only for te single mode fibers only 35. Optical fibers work on te principle of A) Refraction B) double refraction C) reflection D) total internal reflection Dielectric Materials 1. Te unit of dipole moment/unit volume is (a) Coloumb/meter (b) Coloumb/meter 2 Coloumb/meter 3 (d) Coloumb 2. Flux density is related to te electric field as (a) D=E+є (b) D=E-є (c ) D= є/e (d) D =E є 3. Te correct relation among te following 4 equations (a) E= є 0 (є r -1) P (b) (c ) є r =χ -1 (b) P= є 0 (є r -1) E (d) D= є 0 (є r -1) E 4. If te distance between te plates of te capacitor is doubled te capacitance is (a) doubled (b) decreases (c ) alved (d) none of tese 5. In a dielectric polarization is

5 (a) linear function of applied field (b) square function of applied field (c ) exponential function of applied field (d) logaritmic function of applied field 6. Wen a dielectric material is subjected to external electric field te internal field will be (a) lesser tan te applied field (b) greater tan te applied field (c ) same as applied field (d) zero 7. For a given dielectric electronic polarizability α e is (a) Increases wit temperature (b) decreases wit temperature (c ) independent of temperature (d)may increase or decrease wit temperature 8. Electronic polarization (a) Decreases wit increase in temperature (b) Increases wit temperature (c ) independent of temperature (d) may increase or decrease wit temperature 9. In a solid or liquid dielectric wit external applied electrical field as te electronic polarizability α e increases te internal field E i (a) Increases (b) reduces (c) remains constant (d) none of tese 10. Te polarization tat occurs in te frequency range to Hz is (a) electronic (b) orientational (c ) ionic (d) space carge 11. Te energy due to dielectric loss appears as (a) ligt energy (b) eat energy (c ) sound energy (d) electromagnetic energy 12.Ferro electricity is concerned wit te observation of (a) magnetic ysteresis in iron (b) electric ysteresis in iron (c ) magnetic ysteresis in dielectric materials (d) electric ysteresis in dielectric materials 13. All piezoelectric crystals possess (a) a structure wit centre of symmetry (b) a structure wit no centre of symmetry (c ) cubic structure (d) romboedral structure 14. Wic of te following is a piezoelectric materials? (a) lead (b) mica (c ) iron (d ) quartz

6 Magnetic Materials 1. Te relation between B, M and H is (a) H =µ 0 (M+B) (b) M =µ 0 (H+B) (c ) B =µ 0 (H+M) (d) none of tese 2. Te relative permeability for diamagnetic materials is (a) Sligtly greater tan one (b) zero (c ) less tan one (d) very muc greater tan one 3. Spin excange interaction exists in (a) Diamagnetic material (b) paramagnetic material (c ) ferromagnetic material (d) non-magnetic material 4. Hysteresis loss occurs wen te ferro magnetic material is subjected to (a) DC voltage (b) AC voltage (c ) bot (d) none 5. Te area enclosed witin ysteresis curve represents (a) Degree of magnetization (b) energy loss/unit volume (c ) number of domains/volume (d) magnetic flux linkage/unit area 6. For a ferromagnetic substances te curie-weiss law is given by (a) Χ =C/T (b) Χ =C/(T-θ) (c ) Χ = (T- θ)/c (d) Χ= C/(T+θ) 7. Te material in wic te atoms or molecules develop a magnetic moment only in te influence of an applied magnetic field is (a) Diamagnetic (b) paramagnetic ( c) ferromagnetic (d) ferrimagnetic

7 Modern Pysics 1. Rayleig- jeans law explains (a) lower wavelengt region (b) iger wavelengt region (c) bot (d) none 2. Potons are (a) electrically positive (b) electrically negative (c) electrically neutral 3. Te initial kinetic energy of te potoelectrons depends upon (a) intensity of te incident ligt (b) frequency of te incident ligt (c) applied accelerating potential 4. Te wavelengt of de-broglie waves associated wit a moving particle is independent of its (a) mass (b) carge (c) velocity (d) momentum 5 An electron and proton are accelerated troug te same potential difference ten teir de-broglie λ e and λp are related as (a) λ e = λp (b) λ e < λp (c) λ e > λp 6. Wen an electron is accelerated by potential V volts, ten te de-broglie s wavelengt is A 12.27A 122.7A 1227A 0 (a) (b) (c) (d) V V V V 7. Experimental evidence for te existence of matter waves was provided by (a) de Broglie (b) G.P Tomson (c) Davisson and Germer (d) Einstein 8 Electron beaves as waves because tey can be

8 (a) deflected by an electric field (b) diffracted by te crystal (c) deflected by magnetic field (d) tey ionize te gas 9. Group velocity and pase velocity are related as (a) v g > v p (b) v g = v p (c) vg v p (d) v g < v p 10. Te de broglie wavelengt of an electron is 2 A 0. its momentum is (a) 6.6 X10-24 kg-m/sec (b) 3.3 X10-24 kg-m/sec (c) 0.30 X10 24 kg-m/sec (d) 3.3 X10-22 kg-m/sec 11. velocity of matter wave is always (a) lesser tan c (b)greater tan c (d) equals to c (d) none of tese 12. We do not observe matter waves in eavy particle because a. te wavelengt associated is large b. te wavelengt associated is small c. tey travel wit lesser velocity d. none of tese 13. Wen an electron is accelerated, if de-broglie wavelengt is 1A 0, ten te applied voltage is nearly equal to (a) 15V (b) 12V(c) 500V (d) 150V 14. Te wavelengt associated wit a moving particle a. depends upon te carge associated wit it b. does not depends upon te carge associated wit it c. depends upon te medium in wic te particle travels d. none of tese 15. An electron, neutron and a proton ave te same de-broglie wavelengts; wic particle as greater velocity? (a) electron (b) neutron (c) proton 16. Te product of pase velocity and group velocity equal to (a) Partical velocity (b) velocity of ligt (c) square of velocity of ligt

9 17. Te particle velocity of wave is equal to (a) Group velocity (b) pase velocity (c) velocity of ligt (d) velocity of sound 18. Matter waves are present only if te particle is in (a) Equilibrium state (b) metastable state (c) motion (d) none 19. Matter waves are (a) Not mecanical waves (b) mecanical waves (c) eiter mecanical or e.m waves (d) none 20.de-Broglie wavelengt of a particle is independent of te of te particle. (a) mass (b) velocity (c) density (d) carge Quantum Mecanics 1. Te product of uncertainty between two canonically conjugate variables is (a) (b) (c) (d) Te equation of motion of matter waves was derived by (a) de Broglie (b) Heisenberg (c) Scrodinger (d) Davisson 3. Te probability density of a particle associated wit te de broglie wave is given by (a) 2 (b) (c) 2 (d) Te value of energy for wic Scrodinger equation can be solved are called (a) wave functions (b) Eigen functions (c) Eigen values (d) probable values 5. Te energy of te lowest state in one dimensional potential box of lengt a is 2 2 (a) zero (b) (c) (d) ma 2ma 8ma

10 6. In case of free particle te energy values are (a) continuous (b) quantized (c) normalized (d) none of tese 7. te lowest energy of an electron confined in a box of side 0.1nm eac is (a) 119.2eV (b) 112.9eV (c) 119.9eV (d) 102.9eV 8. If te uncertainty in position of an electron is 4X10-10 m, ten te uncertainty in its momentum will be (a) 1.13X10-24 kg m/sec (b) 1.31X10-25 kg m/sec (c) 1.31X10-20 kg m/sec 9. If te uncertainty in te location of a particle is equal to its de-broglie Wavelengt, ten te uncertainty wit its velocity is (a) v/4π (b) v/π (c) v/2 (d) v 10. Te particles tat cannot exist inside te nucleus are (a) protons (b) neutrons (c) electrons (d) potons 11. For a particle wic is not bound to any system and is free,te energy value is (a) Zero (b) finite but not quantized (c) infinity (d) finite but quantized 12. Te wave function is an acceptable wave function if it is (a) finite everywere (b) continous everywere (c) single valued everywere (d) aving all tese properties 13. If te uncertainty in momentum is large, te uncertainty in wavelengt is (a) small (b) large (c) zero (d) none of tese 14. According to Max Born s interpretation 2 represents (a)energy density (b) particle density (c) probability density (d)carge density 15. For a particle in te ground state in one-dimensional potential well of widt a

11 and of infinite eigt, te probability of finding it will be maximum at a distance of (a) a/2 from te wall (c) 3a/4 from te wall (b) a/4 from te wall (d) a=0 from te wall

DUAL NATURE OF RADIATION AND MATTER

DUAL NATURE OF RADIATION AND MATTER Important Points: 1. J.J. Tomson and Sir William Crookes studied te discarge of electricity troug gases. At about.1 mm of Hg and at ig voltage invisible streams called