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exam1solutions - S 0 L, U 7’ / OA/ 8 WW I Physics 273—...

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Unformatted text preview: S 0 L, U 7’ / OA/ 8 WW I Physics 273— Exam I Wednesday, October 5, 2011 Prof. Mohan Kalelkar Your name sticker with exam code . The exam will last from 1:45pm to 2:50pm. Use a # 2 pencil to make entries on the answer sheet. Enter the following id information now, before the exam starts. . In the section labelled NAME, enter your last name, then fill in the empty circle for a blank, then enter your first name, another blank, and finally your middle initial. . Under STUDENT # enter your 9—digit Student ID Number. Under COURSE enter 273. Under CODE enter the exam code given above. 1/! 2 X . During the exam, you may use pencils, a calculator, and ONE 8 11” sheet of paper with formulas and notes. . There are 16 multiple—choice questions on the exam. For each ques— tion, mark only one answer on the answer sheet. There is no subtrac— tion of points for an incorrect answer, so even if you cannot work out the answer to a question, you should make an educated guess. At the end of the exam, hand in only the answer sheet. Retain this question paper for future reference and study. . Useful numerical constants are given on the next page. Before starting the exam, make sure that your copy contains the page of constants and all 16 questions. Bring your exam to the proctor if this is not the case. Elementary charge 6 = 1.6 X 10‘19 C 1 electron volt (6V) = 1.6 X 10‘19 J Speed of light 0 = 3 X 108 m/s Planck’s constant h = 6.63 X 10"34 J ~ 8 = 1240 nm - eV/c h = h/27r Compton wavelength of electron h/mc = 0.0024 nm Ground—state energy of hydrogen = —13.6 6V Rydberg constant R = 0.0109678 nm‘"1 Avogadro’s number = 6.02 X 1023 molecules/mole Electron mass = 9.11 X 10"31 kg = 0.511 MeV/c2 Proton mass = 1.673 X 10”27 kg = 938.3 MeV/c2 Neutron mass = 1.675 X 10—27 kg = 939.6 MeV/c2 ‘ Atomic mass unit 1 u = 931.5 M eV/c2 1010000 Powers of ten: femto(f) ) nano(n) micro(g milli(m) 10—12 10—9 10‘6 10—3 centi c) kilo(k) Mega(M) Giga(G) Tera(T) 10—2 10+3 10+6 10+9 10+” 10—15 1. . A spaceship of proper length 50 m is moving away from the earth at a speed of 0.8a. According to observers in the ship, their journey takes 60 hours. According to observers on earth, What is the length of the ship, and how long does the journey take? 83 m; 10 hours 30 m; 3.6 hours 83 m; 3.6 hours 50 m; 3.6 hours 30 m; 10 hours ~—'««> a b c d e ) ) ) ) ) 2. A truck of proper length 20 m approaches a bridge of proper length 18 m, Which is at rest on the earth. According to observers on earth, the truck and the bridge are equal in length. What is the length of the bridge as measured by the truck driver? ) -> a b c d e ) ) ) ) About 16.2 m About 18.0 m About 19.8 m About 7.9 m About 10.0 m 3,0. I? h, to, LT a 3. A spaceship is moving away from earth at 0.3c. Its rebellious commander fires a torpedo back towards the earth at a speed of 0.5a relative to the ship. What is the speed of the torpedo relative to earth? KCW} K/fiwl ~a>> a b c d e ) ) ) ) ) About 0.94c About 0.80c About 0.70c About 0.24c About 0.17c 65L 4. A student steps into a library at Rutgers. 150 as later (as measured on earth), another student steps into a library at Columbia University, located 60 km from Rutgers. Find the speed of a reference frame, moving along the line from Rutgers to Columbia, in Which these two events are simultaneous. Me DA 0 O" 93 Vvvvv CD About 0.75c About 0.80c About 0.85c About 0900 About 0.95c Act/:- V642” “5 TAX) C2. 5. In an inertial reference frame K, two events occur on the X~axis separated in time by At and in space by A33. In another inertial reference frame K’, moving in the X—direction relative to K, the two events could occur at the same time under which, if any, of the following conditions? a)_ For any values of A93 and At r; j; C: a. «a h) Only if |Aas/At|>c vi z W)“ K’ W A a c) OnlyifIAzr/Atl<c we . _ VAX f, 91E 5: ./ > c. d; Only 1f|A33/At| ——c Av A/}/ 7/, m ,9 A76. ,2}, e Under no conditions 62 6. A particle of mass M has a momentum of 2Mc. If the momentum is then doubled, by what factor does its total energy increase? a) About 1.41 E :3" (1M9)2C2’+'MQCZ’L :1 ffflcg. ab) About 1.84 _ c) About 2.00 5/; lemcf‘cfl +Maczf S WNGQ d) About 4.00 ‘ ) e None of the other answers I :3- .g-gc‘» I I 31/“ 7. A particle of mass M has a kinetic energy of 3MCZ. In which of the following ran es does its s eedv lie? 2 g) 080p EfiBNca-PManfiéme a v< . c r _ 0.8OCSv<0.85c ,3 : {ZHVI an): _‘ maczf :5; {fl/Ema 0.850 S 'u < 0.900 b) c) 2 r d) 0.90c g 'u < 0.950 C ,5 J e).vZO_95c ’U’: 78E?! 5 TEACH 0.77:: ~ , we 8. A particle of mass m has a momentum of 27:10. What is its kinetic energy? a) About 2.24mc2 _ Z L . 1 1+ “— C9, b) About2.00mc2 E: [2 “Q C 4’ m C 1.- J5?" -> c) About 1.24ch 2 a Z d) Aboutmc2 ' K: JET’MC wmc 7: [.Z‘fMCr e) About 3.00mc2 9. A particle of mass 498 M eV/ 02 is at rest. It spontaneously breaks into two fragments of equal mass, moving in opposite directions at equal speeds of 0.830. What is the mass of either fragment? (Note that “mass” means “rest mass”). _ . I 1 _ if; a) 139 MeV/c2 W W: Mag»; ymc1+ yrwm b) 1671\JeV/c2 r? I,” F...” . "r I f C) 'Illelf/C2 Yr) 2X 2” lw[’ ~ 7'76' d) 278 MeV/c2 M 8 _ e) MGV/CZ m ’5 7; q [VI-61%;; ' (9)0, 76:) 10. A photon strikes an electron of mass m that was initially at rest, creating an electron—positron pair. The photon is destroyed in the collision, and the "L~ F final state consists of the positron and two electrons, all of which have the Q 7’ 3 Y same mass m. They also haveequal- speeds and all move along the initial 4 E; direction of the photon. What was the photon’s energy? _ 7; 3 C a) me2 W own/$.25 +MC253 (Ey)9'£ .9. 9‘ , —-—~—— C b) ZmC2 X 3c: G + m 2 @3ch ,1 24 2 m u m: -~>d)4mcg EY+2mc Ey+mc $fl(~:Mé>’—l~ma éj e) 5mc2 9v 2 4. 2 H 2 M C E: :3 $14) a .fi ~17 x :2“? gy ..... 44 m6 11. An astronomical object emits light of wavelength 121.5 nm. An observer on Earth measures the wavelength of the light received from the object to . . . 7 a be 607.5 nm. What is the velocity of the object. M H w 9 b a) About 3.0 X 108 m/s away from Earth Lv-E M 1m ' g 5} 3 - 8 / 2 b) About 2.4 x 108 m/s away from Earth Hg 5 2 50 _fl) 5; (g ,r . -§ C) About 2.8 x 10 m/s away from Earth g d) About 2.4 x 108 m/s toward Earth { 913X3 X ,9 8) :3 .1 g >4/o m/j e) About 2.8 X 108 m/s toward Earth 7r"; ' l2. laser is emitting 10l7 photons every second, all at a wavelength of 633 nm. What is the laser’s power output? a) About 0.75 W #7 b) About 0.03 W V c) About 12 W [p 7: N {.62. d) About 0.20 W /\ £33 x/p'fi N '03 M‘ _ a to”) 13. The threshold wavelength for photoemission in silver is 262 nm. For what wavelength will the photoelectric stopping potential be 1.36 V? fia) About 204nm (171;; 16,2 5; 7349 W,§y. C b) About 175 nm /\ p _ a 1 if 73 31/ c) About 368 nm I . 25'?“ W ‘ , f (1) About 912 nm 5),, r 4>+ 5V9 :2 4.73 +1.35 >- g [9ng e) About 127 nm A ’60 [52425 I ‘ ,7, ,__/- .— gzr / 76.05] :2 gsz/L‘m/Wl- 14. In a photoelectric effect experiment, which of the following changes would cause the stopping potential to INCREASE? o I: Increasing the frequency of the light 0 II: Increasing the intensity of the light 0 III: Using a different metal with a smaller work function a) Ionly xfiv :: b) I and II, but not III c) II and III, but not I p—é d) I and III, but not II e) All three would cause the stopping potential to increase 15. A photon moving at speed c makes a Compton collision with a free electron at rest. After the collision, the scattered photon travels at an angle 9 relative to the direction of the incident photon. What is the speed of the scattered photon? a) c cos (9 , » l b) c(1~cos9) «é W M C ' c) 0 sin (9 d) c (1 ~ sin 9) V? 6) None of the other answers 16. A photon of wavelength 0.0016 nm undergoes Compton scattering off a free electron initially at rest. The scattered photon emerges at an angle of 60° with respect to the incident photon direction. What kinetic energy does the electron acquire? ‘ a) About 1.22 MeV 7 $2 =1 WIQI—Dx/Dvg 7.: .775 Way. m; b About 0.33 MeV . 001K About 0.44 M eV ~e About1.03MeV r ,WQSZW. M E”: 1%22g—«afl42/M Th K¢ gag/:- .775w.1fl{’3—:,331 0421/. l c) About 0.77 MeV A’,; A4, gig—u (Page); ,DD/g-f— .Dbfllffirdwévp) ) C ) ...
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This note was uploaded on 01/15/2012 for the course PHYS 273 taught by Professor Kalekar during the Fall '09 term at Rutgers.

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exam1solutions - S 0 L, U 7’ / OA/ 8 WW I Physics 273—...

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