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Unformatted text preview: Concepts of Physics: Class Test III 28 November 2011 Soluh'm V Z. Name: Instructions 0 There are 9 questions on 5 pages. Total: l‘ Show your reasoning and calculations and always justify your answers. Physical constants and useful formulae distance traveled eed =
Sp time elapsed speed of light 2 wavelength x frequency speed of light frequency : wavelength photon energy 6.6 X 10—34 x frequency photon energy
6.6 x 10—34 6.6 x 1034
mass >< speed 6.6 x 10'34
mass photon frequency particle wavelength 2 position range )1 velocity range m Speed of light: _d
3'1:
c=/\><f
C
f‘X
E=6.6x10‘34xf
E
f' 6.6x1034
A=6.6><10‘34
mxv
—34
Amxsz——6'6X 10
m c = 3.0 x 108 m/s Phys 100
Fall 2011 Question 1 Light travels toward an arrangement of barriers
and slits as illustrated. The intensity proﬁle of the
light on the screen is as illustrated. Three points
are marked on the screen. Which of the following
(choose one) is true? T."
A B c
— _ — BaJTier/slits a) Each photon that hits the screen moves from left to right across the screen with a wavy
pattern.
b) Any photon that reaches the screen will hit the screen and move toward point B. c) Each photon that hits the screen arrives at point A and also point B and also point C.
d) A photon that hits point A on the screen will not also hit point B. Question 2 Light travels toward an arrangement of barriers and
slits as illustrated. There is a gate over the right slit
which enables the right slit to be opened or closed.
When both slits are open1 the intensity proﬁle for the
light is illustrated by the solid blue curve. When just
the left slit is open, it is illustrated by the dashed red
curve. _ _  Barrier/slits a) Indicate the location on the screen (with the symbol “A”, in the diagram) where the
photon is most likely to arrive when both slits are open. Screen b) Indicate the location on the screen (with the symbol “B”, in the diagram) where the
photon is most likely to arrive when only the left slit is open. c) An experimenter thinks that when both slits are open there are more ways for any
photon to reach the screen than with just one slit open. Thus he says that, with both
slits open, the photon will be able to arrive at any location where it could have arrived
with just the left slit is open. Is this true or false? Explain your answer. Question 3 Red light has a frequency of 4.6 x 1014 Hz and ultraviolet light has a frequency of 1.9 x 1016 Hz.
Which of the following (choose one) is true? a) The energy of a photon of red light is always larger than that of a photon of ultraviolet
light. b) The energy of a photon of red light is always smaller than that of a photon of ultraviolet
light. c) The energy of a photon of red light is larger than that of a photon of ultraviolet light
only if the intensity of the red light is larger than the intensity of the ultraviolet light. d) The energy of a photon of red light is smaller than that of a photon of ultraviolet light
only if the intensity of the red light is smaller than the intensity of the ultraviolet light. /4 Question 4
A yellow light produces electromagnetic radiation of wavelength 6.0 x 10“7 m. a) Determine the energy of each photon of the yellow light. b) The light produces 5.0 X 1020 photons every second. Determine the total energy produced
by the light in one second. Question 5 Neutrons are ﬁred, one at a time, directly toward
a barrier which contains two slits. The probability
distribution (proﬁle) for the arrival of neutrons at a
screen (of neutron detectors) is illustrated in the dia
gram. Which of the following (choose one) is true? A B   _ Barrier/slits a) Neutrons must arrive directly opposite the slits so none will arrive at A or at B. b) Every neutron will arrive at A and at B.
c) Any neutron could arrive at A but it is just as liker to arrive at B. @Any neutron could arrive at A but it is more likely to arrive at B. /4
Question 6 The mass of a neutron is 1.67 x 10—27 kg. a) Determine the speed with which the neutron must move in order to have a wavelength
of 6.5 x 10'7m (the same as that of red light). b) \Vhich of the following (choose one) is true is the neutron is replaced by an electron
(mass 9.11 x 10—31 kg) traveling at the same speed? £16 MO '51
wavelet51k: i) The electron has a. smaller wavelength than the neutron. “4433 K Valoa’lj
ii) The electron has a larger wavelength than the neutron. fly/v iii) The electron has the same wavelength as the neutron”. ""/ /
Ln W55 f” N /8
lwgcr wavelength Question 7 Protons, whose masses are 1.67 X 10—27 kg, are cooled so that their velocities approach
0.00 m/s. The cooling process is imperfect and the uncertainty in each protons velocity is
2.0 x 10’5 m/s (at most). Determine the uncertainty in the position of each proton. 6.654044 9.6 no“ Wailing Foahaa x Mariana 5M = .____ .. 2 338,05}
W” LLMO'”
Maxims: Mbe 2.0.406 = 3.613 «(0"r
2.0):{0’5 'Z.c5‘a<f.0'f ‘—"D Warming .: ZaOKiOFZM /6 Question 8 The energy level diagram for an atom is as illustrated. LEV—Bl 3 80 X 10—19 J
The energies are indicated alongside the levels. Which A 2 0): [CII:l
of the following (choose one) is true? LBVGI 2 —' 6.0 x 10‘19 J Emma/o} .: (1W 455M. may? 9 3.0 XlOﬁ Level l —— 3.0 x 10‘19J é Y r‘ H h u u
largo change in abm. wag/3. =0 Wat? . ’2~Pl has [anag (new?! chm“
a Light emitted in the jump 2 —> 1 has the same frequency as 3 —+ 2.
 b) Light emitted in the jump 2 —> 1 has a larger frequency than 3 —> 2.
c) Light emitted in the jump 2 —> 1 has a smaller frequency as 3 —> 2. /4 You are given the atomic spectra for several elements, including sodium, mercury and potas
sium. You are given an unknown powdered material which you can burn safely. Describe how
you could determine whether the powder contains sodium by using the light that is produced
when it burns. Question 9 I) Bum 1:0de
7.) Observe. k3“ + 63d 3W
5) If sreclml lines fursodim queN, Walt central/‘5 5000M. /4 ...
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 Fall '11
 collins
 Physics

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