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Unformatted text preview: S 0 L, U 7’ / OA/ 8
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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 1fA33/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 .ggc‘» 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 EﬁBNcaPManﬁéme
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 [VI61%;; ' (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 LvE 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/gf— .Dbﬂlfﬁrdwévp)
) C
) ...
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