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Unformatted text preview: 9“ 5’?” Physics 228 — Exam 2 ‘
8 April 2010
Profs. Babe and Coleman => Your
name
sticker
with
exam
code => SIGNATURE Turn off and put away cell phones now! The exam will last from 9:40pm to 11:00pm. 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 (Last, First, MI.) 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 9digit student ID. Enter 228 under COURSE, and your section number (see label
above) under SEC. Under CODE enter the exam code given above. During the exam, you may use pencils, a calculator, and one
handwritten 8.5 x 11 inch sheet with formulas and notes, with
out attachments. There are 16 multiple—choice questions on the exam. For each
question, mark only one answer on the answer sheet. There is no
deduction 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 ened of the exam, hand in the answer sheet and the cover page. Retain this question paper for future reference
and study. ‘ When you are asked to open the exam, make sure that your copy
contains all 16 questions. Raise your hand if this is not the case,
and a proctor will help you. Also raise your hand during the exam
if you have a question. Please SIGN the cover sheet under your name sticker and have
your student ID ready to show to the proctor during the exam. Useful information 6 = speed of light = 3.00 x 108 m/s qe —e = charge on an electron = —1.602 x 10‘19 Coulombs
qrp = +6 = charge on a proton = +1.602 x 10‘19 Coulombs
me = electron mass = 9.11 x 10—31 kg mac2 2 electron rest energy = 0.511 MeV m,9 = proton mass = 1.67 x 10‘27 kg mpc2 = proton rest energy = 938.27MeV mncz = neutron rest energy = 939.57MeV k3 = Boltzmann’s constant = 1.38 x 10‘23 J / K Wien’s Constant = 2.898 X 10‘3m  K a = Stefan’s Constant = 5.670 x 10‘8W/(m2K4)
h = _.
h = glaze x 1034 J—s h = 4.136 x 10—15 eVs (in units of electron volts—second)
he = 1240 eV  nm = 1240 MeV  fm 1 nm = 10—9 m 1.4 =1010 m = 0.1 nm 1 pm = 10‘6m 1 mHZ = 10‘3 HZ
1 MHZ = 10+6 Hz 1 kHz = 10+3 HZ
1 GHZ = 10+9 HZ A photon, an electron, and a baseball have the same momentum.
Which has the largest de Broglie wavelength? ‘ a) photon . F
'
c) electron 1 ' SQ W MOW“? «WM "7 5V “"2 A v
d) baseball and electron I
e) baseball A particle is conﬁned inside a cube of side length L, with one
corner at the origin. The potential height of the walls of the cube
is inﬁnite. The normalized wave function of the particle, which is
in the ground state, is 2 3/2 ‘ ¥ 2. 5 , 'L . 2.7T ylhz’ng
¢($,y,z) 2 (~) sinwxsinﬁysinwz, O < 2:, y, z < L V g; ' 5’” ﬁx 3"“ )l 3
L ‘ '7— L ch§5¥%/'§¥Z~):g
What is the maximum value of the probability distribution "func— ‘ 51:? S 1. 5 Omax (/0 L ' [3"
tion for an electron in this state? ' A perfectly black body at a temperature of 100°C emits light (/96 Wl‘ey‘ [aw KmTa x a m K of intensity I that has strongest intensity at wavelength A. The temperature of the black body is now increased to 200°C. The .5 p ‘3 5
hotter black body now emits light most strongly at a wavelengt A heifer c 2. X /0 '3  closest to)‘  A K .53 3'5 . > . .  A c) 2A d 1.3A An elementary article with rest mass m spontaneously decays
. Par?! ﬁg m . . .
into two m With rest masses —. What are the kinetic energies A 3
of these particles? 93:14:12 a) E, me 32 T
b) "1782,02
c) “L
e) %,0 If light incident on a metallic surface is doubled in intensity, the
maximum kinetic energy of electrons produced by the photoelec
tric effect will change from K to: a) 4K
b) 2K
c) K /4 d ) K 2
e) K no change) As a spaceship heads directly to earth at a velocity of 0.8c, it
sends a radio signal to earth. When those radio waves arrive on
earth, their velocity relative to earth is: ' a c2 + 11%; , where ’UE is the velocity of the earth. c) _ \/ (.8c)2 + 01%; , where ’UE is the velocity of the earth.
d) 1.8 c. s a 
e) 0.8 c. Accelerating voltages in cathode—raytube (CRT) TV’s are about
24.0 kVr What is the shortest wavelength of the X~rays that are
produced when the accelerated electrons hit the screen? a) 52nm
b) 5.6 x101st ci 0.008nm e) 7.8nm . K K
a <""‘° H Me? = ﬁlCZ‘l’ K)"2 K: MC?" M 6; ouywhj eke/Mas MAME
on? on ’F o incommj 0431M“, mt I. 7A2 SPeed 6F @144" f5 ‘0 m w “famq ##3' f 1 energy cl, mmmlvxg ~9le iS 24%105 Cl/ ajsume W mnWUfM (( my f» 56nch Pliers”!
E=hc >\= he 2 (mo €V'nm s 0.05M»
7: “1;— 24000 €\/ 10. V 11. A meter stick moves in the laboratory along the direction of its ‘ _
length With a speed of 1.2 x 108 m/sec. Its length, as seen by an . observer at rest in the laboratory, is: a) 1.09 m
b) 1.19 m
d) 0.84 m
e) 1.00 m A hydrogen atom undergoes a transition from the n '=' 6 to the
n == 2 state by emitting a photon. According to the Behr model
of the atom, if the angular momentum'is conserved,’ What is the
angular momentum of the photon that is emitted? a) 371
b 0n
c) 4 d) 1%
e) 271 The uncertainty in position of an electron in a certain state is
5 X 10‘10 m. The uncertainty in its momentum (in kgOm/s) must
be: a) less than 10‘23 b) greater than 10“20 c) less than 10‘25 ﬂ ; eater than 10‘25 . e) greater than 10“23 Consider an electron With the freeparticle wavefunction
2M1", t) = Aexp[i(kx — wt)]. Which of the following is false? a) the energy of the electron is ﬁw. b) ‘A can be chosen to be a pure imaginary number. 0 "Mac, t) is not a stationar state. 4 d the momentum of the electrOn is his . e) the probability distribution function is independent of as. Wt =A*A 12. 13. 14. 15. An electron is trapped in a onedimensional inﬁnite potential well
of Width 10‘10 m. What is the energy of the photon emitted when
the electron makes a transition from the ﬁrst excited state (n =
2) to the ground state (n z 1)? a) 0.062 eV b) 37.4 eV
' ' d) 127 eV e) 150 eV A distant star is receding from earth at a speed such that the V  '
434—nm emission line of hydrogen is Doppler shifted to 650 nm. At what Speed is the star receding? a) 0.6670 b) 0.3830 e) 0.9950 c) 0.9999c d) 0.5c r The Wave character of electrOns is best illustrated by which of the following? a The fact that hot objects emit electromagnetic radiation.
@The diffraction pattern observed when a beam of electrons is scattered by a crystal.  ' c) The scattering of alpha particles from gold foil. d)_ The ejection of electrons from a metal surface illuminated
by light. e) The fact that a rainbow consists 'of a continuous spectrum
of colors. ' rpm) is the normalized wave function. for a particle moving along
the cc axis. The probability that the particle is in the interval from
wzatomzbisgivenby: do wow—wow
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+2. Eng: ﬁll ' 2W?» 2. 4923 la ’2.
W2 .Zm L2. _‘ 3
$139on lSet/z: *4.626X/0 93—5
7.1/ m2 “Wk5  Io‘z°m 2.. _ —u' :C+u;\
Jawléwﬁe/l 2:67 ° '_ diﬁ‘m 0507‘ [5' a wave b
fZLde .—
_a §§a5;22% . . c+u i"
 6’“ 43‘} b jlvsﬂta 0v 16. A spaceship is moving at speed 0.700 to the right relative to earth.
Standing at the rear of the ship, a woman ﬁres a space gun,‘ and the
bullet goes forward inside the ship at a Speed of 0,900 relative to
the spaceship. What is the bullet’s speed as measured from earth? 0.7c.< ...
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 Spring '10
 KARINRABE
 Physics

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