No. of Printed Pages : 7 BACHELOR OF SCIENCE (B.Sc.) Term-End Examination December, 2013 PHYSICS

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1 No. of Printed Pages : 7 BACHELOR OF SCIENCE (B.Sc.) Term-End Examination December, 2013 PHYSICS PHE-09 PHE-09 : OPTICS Time : 2 hours Maximum Marks : 50 Note : All questions are compulsory but there are internal choices. The marks for each question are indicated against it. You can use log tables or a calculator. Symbols have their usual meaning. 1. Attempt any five parts : 3x5=15 (a) State three important differences between interference fringes obtained by a biprism and a Lyod's mirror. (b) Explain the importance of coherent sources in interference phenomenon. (c) The coherence length for sodium D2-line is 2.5 cm. Calculate the coherence time ic and the spectral width of the line. Take X=6 x 10-5 cm. (d) The energy radiated by the sun is approximately 4 x 1026Js -1. If the sun is assumed to be sphere of radius 7 x 108m, calculate the Pyointing vector at its surface. PHE-09 1 P.T.O.

2 (e) Calculate the radius of the first and third zones in a zone plate of focal length 20 cm for light of wavelength 5000A. (f) (g) (h) What is dichroism? Give an example of dichroic material. State the salient features of the observed Fraunhofer diffraction pattern of a single vertical slit illuminated by a point source. Discuss the applications of lasers in medicine. 2. Explain the phenomenon of double refraction. 5 What are positive and negative crystals? Draw the o - and e - wave surfaces in positive and negative uni-axial crystals. OR What is a quarter wave plate? Calculate the 5 thickness of a quarter wave plate for light of wave length 5000 A. The refractive indices for o-ray and e - ray are and respectively. 3. Answer any two parts : 5x2=10 (a) In Newton's rings experiment prove that the radius of the dark ring is proportional to the square root of the natural numbers. PHE-09 2

3 (b) (c) Distinguish clearly between fringes of equal thickness and fringes of equal inclination. Briefly describe an experiment to demonstrate them. Explain the principle of Fabry Perot interferometer. Obtain an expression for the intensity of the Fabry Perot fringes. 4. State the salient features of Fraunhofer double slit 3+7 diffraction pattern. Obtain an expression for the intensity of a double slit diffraction pattern. OR The objective in a telescope is bigger than the 3+7 eye-piece. Explain it importance with reference to a astronomical telescope. Compare the performances of two telescopes with objectives of aperture 50cm and 100cm. Assume that their focal lengths are equal. 5. Answer any two parts : 5x2=10 (a) Using the stellar interferometer, Michelson observed for the star Betelgeuse that the fringes disappear when the distance between movable mirrors is 65 cm. Assuming l. = 6 x 10 5cm, calculate the angular diameter of the star. PHE-09 3 P.T.O.

4 (b) With the help of a schematic diagram, discuss the recording of a hologram. If the angle subtended at the hologram by the signal and the reference beam is 15, what is the wave length of light used which produces fringes separated by a distance 1.811m? (c) An optical fibre consists of a core of refractive index n1 and cladding of refractive index n2. Derive an expression for the maximum angle of incidence that a ray can move with the fibre axis such that it is guided through the fibre. PHE-09 4

5 ft-x4!rich ) TIT11TT fq.4trit, aqui 111%79'1.-09 : ict) tvher : 2 Vr4 3TAIW W : 50 Tr9fr so'-f arfq-arei <*g artd-ftw 777 ei 5R-1 311W 374- R7774 A'k, Tuf cif,/ W1TUNT 372IW 4)(-35c-ie dqq)4/ W-( g yrue * tvbqfrei atef 1. fay lifw ITO alit fe4 : 3x5=15 (a) fgwfg- T. P-TT (-11 q Tui ircichtull afḏ7 401 (b) ceircichut NRNe.-ii ch(11(1.014 #ral I (c) kirviii D2-tai* ki1 cholkici4cilit 2.5 cm t I choiriesgscii Tc 2.T1.4gt T t0 lifichroci I Rqi t x= 6 x10-5 cm. (d) gri dc<llizfcf TIT1T 4 x 1026Js -1 ti eirc (1,4 -NwIT 7 x 108 m (=t) Tirff fffzit ITT Lcqr44i1,11-q7P-Iiichroci I PHE-09 5 P.T.O.

6 (e) c-i A t 20 cm ittt1 tt TI)-1--ati;r21-442TTI-61-zr ch Cid stqutdt wt? f-g-q-crff 1, 7-*7-Tr ruff t1-ur alitin (medicine) A t 31TRI c) f-dtffr-{ I 2. I %.1-97:1- f- 2.T1 itu110-ich 5? tr9t(te 2.1T 7tTV r9h t 0 - 'We - I Tr-dt 31-fttru =f.)11 MT-4T =.1q2TNT c-141 titwf qz3it i1c11? 5000Aqr 5 YchR1 rmi.vt-tnt 71fr*-1 14-e-r1 4Renfi-id cith 0-fwToi e - ft-tur ff2TT t I 3. ftt '41 ITT Tff t 37R f-0-4 : 5x2=10 (a) 9.q7- (7-1 4f 1; i ft:1z 3itta m1 i~l~ll, arfrff c1 t I (b) 2,1F r9f-d -ft; -44 af-d-{ -4d-t --vrf4 9trr #R-Ttu f-q--qtar -k I (c) 4e. <A tf ft-41'ff -F, ci.;) tqat oti\act, PHE-09 6

7 4. rg.(gir%f le.4 *WI 3TFIT-TuT " rg-4g6.9 fd-q-49 Az4.1.>1 tq-df FMS 04,mor) 3TPTIT (5,1c-1q {qqfTi 40i -44 Ik I t1-00, f7-4 T-T- 50 cm ath 100 cm ch ci-c rch q.) ai-firstta ct) tht*71 t1 GRIGIttl 5. ftt t 1.74 t d-c-r fffd : 5x2=10 (a) TT -47T oirdch(uih4 r 31:171)T1 4-iichri-1-1 -r-*rr rch -F50 ciq q?r )-11c1-01)t -cr ct> cm 6) 1 X = 6 x 10-5 cm di T.W)11114 ogri tch 4) I (b) aitg oh) (-1V-Ic11-4 tf-0) cifwzrr chl clai qrktitff.fftri f T ail t-a1171 IR 15 ch)uf 3-tdftff.WT.th -511:Fff NcI-01 air.trrkvi Lirkchrod cra IITN 14-9-*r Nchlkl gri 3c4^i ft-a' t µmti (c) f*-111- AchliskIch c c sh)5 379t n1 t -ff4t Tfit 3Tft fw n2 t I Nchlkl f-*7-7 c c TR 31777'i 3TRT-*--T4 Qui i rc-r.4\ich ml F=.Ri Qui TR aucrfa-ff Ala TR Mchlkf f*-114 t PHE-09 7

PHY410 Optics Exam #3

PHY410 Optics Exam #3 NAME: 1 2 Multiple Choice Section - 5 pts each 1. A continuous He-Ne laser beam (632.8 nm) is chopped, using a spinning aperture, into 500 nanosecond pulses. Compute the resultant