Download answer-Modern-physics

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Objective Questions
1. denotes answer available in Student Solutions Manual/Study Guide
1. (i) Does the speed of an electron have an upper limit?
(a) yes, the speed of light c (b) yes, with another value
(c) no (ii) Does the magnitude of an electron’s momentum have an upper limit? (a) yes, me c (b) yes, with
another value (c) no (iii) Does the electron’s kinetic
energy have an upper limit? (a) yes, me c 2 (b) yes, 12m e c 2
(c) yes, with another value (d) no
2. A spacecraft zooms past the Earth with a constant
velocity. An observer on the Earth measures that an
undamaged clock on the spacecraft is ticking at onethird the rate of an identical clock on the Earth. What
does an observer on the spacecraft measure about
the Earth-based clock’s ticking rate? (a) It runs more
than three times faster than his own clock. (b) It runs
three times faster than his own. (c) It runs at the same
rate as his own. (d) It runs at one-third the rate of
his own. (e) It runs at less than one-third the rate of
his own.
3. As a car heads down a highway traveling at a speed v
away from a ground observer, which of the following
statements are true about the measured speed of the
light beam from the car’s headlights? More than one
statement may be correct. (a) The ground observer
measures the light speed to be c 1 v. (b) The driver
measures the light speed to be c. (c) The ground
observer measures the light speed to be c. (d) The
driver measures the light speed to be c 2 v. (e) The
ground observer measures the light speed to be c 2 v.
4. A spacecraft built in the shape of a sphere moves past
an observer on the Earth with a speed of 0.500c. What
shape does the observer measure for the spacecraft as
it goes by? (a) a sphere (b) a cigar shape, elongated
along the direction of motion (c) a round pillow shape,
flattened along the direction of motion (d) a conical
shape, pointing in the direction of motion
5. An astronaut is traveling in a spacecraft in outer space
in a straight line at a constant speed of 0.500c. Which
of the following effects would she experience? (a) She
would feel heavier. (b) She would find it harder to
breathe. (c) Her heart rate would change. (d) Some
of the dimensions of her spacecraft would be shorter.
(e) None of those answers is correct.
6. You measure the volume of a cube at rest to be V0. You
then measure the volume of the same cube as it passes
you in a direction parallel to one side of the cube. The
speed of the cube is 0.980c, so g < 5. Is the volume you
measure close to (a) V0 /25, (b) V0 /5, (c) V0 , (d) 5V0 , or
(e) 25V0?
7. Two identical clocks are set side by side and synchronized. One remains on the Earth. The other is put into
orbit around the Earth moving rapidly toward the east.
(i) As measured by an observer on the Earth, does the
orbiting clock (a) run faster than the Earth-based clock,
(b) run at the same rate, or (c) run slower? (ii) The
orbiting clock is returned to its original location and
brought to rest relative to the Earth-based clock. Thereafter, what happens? (a) Its reading lags farther and farther behind the Earth-based clock. (b) It lags behind
the Earth-based clock by a constant amount. (c) It is synchronous with the Earth-based clock. (d) It is ahead of
the Earth-based clock by a constant amount. (e) It gets
farther and farther ahead of the Earth-based clock.
8. The following three particles all have the same total
energy E: (a) a photon, (b) a proton, and (c) an electron. Rank the magnitudes of the particles’ momenta
from greatest to smallest.
9. Which of the following statements are fundamental
postulates of the special theory of relativity? More than
one statement may be correct. (a) Light moves through
a substance called the ether. (b) The speed of light
depends on the inertial reference frame in which it is
measured. (c) The laws of physics depend on the inertial reference frame in which they are used. (d) The
laws of physics are the same in all inertial reference
frames. (e) The speed of light is independent of the
inertial reference frame in which it is measured.
10. A distant astronomical object (a quasar) is moving away
from us at half the speed of light. What is the speed of
the light we receive from this quasar? (a) greater than c
(b) c (c) between c/2 and c (d) c/2 (e) between 0 and c/2
Objective Questions
1. denotes answer available in Student Solutions Manual/Study Guide
1. Rank the wavelengths of the following quantum particles from the largest to the smallest. If any have equal
wavelengths, display the equality in your ranking.
(a) a photon with energy 3 eV (b) an electron with
kinetic energy 3 eV (c) a proton with kinetic energy
3 eV (d) a photon with energy 0.3 eV (e) an electron
with momentum 3 eV/c
2. An x-ray photon is scattered by an originally stationary
electron. Relative to the frequency of the incident photon, is the frequency of the scattered photon (a) lower,
(b) higher, or (c) unchanged?
3. In a Compton scattering experiment, a photon of
energy E is scattered from an electron at rest. After
the scattering event occurs, which of the following
statements is true? (a) The frequency of the photon is
greater than E/h. (b) The energy of the photon is less
than E. (c) The wavelength of the photon is less than
hc/E. (d) The momentum of the photon increases.
(e) None of those statements is true.
4. In a certain experiment, a filament in an evacuated lightbulb carries a current I1 and you measure
the spectrum of light emitted by the filament, which
behaves as a black body at temperature T1. The wavelength emitted with highest intensity (symbolized by
lmax) has the value l1. You then increase the potential difference across the filament by a factor of 8, and
the current increases by a factor of 2. (i) After this
change, what is the new value of the temperature of
the filament? (a) 16T1 (b) 8T1 (c) 4T1 (d) 2T1 (e) still
T1 (ii) What is the new value of the wavelength emitted with highest intensity? (a) 4l1 (b) 2l1 (c) l1 (d) 12l1
(e) 14l1
5. Which of the following statements are true according
to the uncertainty principle? More than one statement
may be correct. (a) It is impossible to simultaneously
determine both the position and the momentum of a
particle along the same axis with arbitrary accuracy.
(b) It is impossible to simultaneously determine both
the energy and momentum of a particle with arbitrary
accuracy. (c) It is impossible to determine a particle’s
energy with arbitrary accuracy in a finite amount of
time. (d) It is impossible to measure the position of a
particle with arbitrary accuracy in a finite amount of
time. (e) It is impossible to simultaneously measure
both the energy and position of a particle with arbitrary accuracy.
6. A monochromatic light beam is incident on a barium
target that has a work function of 2.50 eV. If a potential difference of 1.00 V is required to turn back all the
ejected electrons, what is the wavelength of the light
beam? (a) 355 nm (b) 497 nm (c) 744 nm (d) 1.42 pm
(e) none of those answers
7. Which of the following is most likely to cause sunburn
by delivering more energy to individual molecules in
skin cells? (a) infrared light (b) visible light (c) ultraviolet light (d) microwaves (e) Choices (a) through
(d) are equally likely.
8. Which of the following phenomena most
demonstrates the wave nature of electrons?
photoelectric effect (b) blackbody radiation
Compton effect (d) diffraction of electrons by
(e) none of those answers
clearly
(a) the
(c) the
crystals
9. What is the de Broglie wavelength of an electron
accelerated from rest through a potential difference
of 50.0 V? (a) 0.100 nm (b) 0.139 nm (c) 0.174 nm
(d) 0.834 nm (e) none of those answers
10. A proton, an electron, and a helium nucleus all move
at speed v. Rank their de Broglie wavelengths from
largest to smallest.
11. Consider (a) an electron, (b) a photon, and (c) a proton, all moving in vacuum. Choose all correct answers
for each question. (i) Which of the three possess rest
energy? (ii) Which have charge? (iii) Which carry
energy? (iv) Which carry momentum? (v) Which move
at the speed of light? (vi) Which have a wavelength
characterizing their motion?
12. An electron and a proton, moving in opposite directions, are accelerated from rest through the same
potential difference. Which particle has the longer
wavelength? (a) The electron does. (b) The proton does. (c) Both are the same. (d) Neither has a
wavelength.
13. Which of the following phenomena most clearly
demonstrates the particle nature of light? (a) diffraction (b) the photoelectric effect (c) polarization
(d) interference (e) refraction
14. Both an electron and a proton are accelerated to the
same speed, and the experimental uncertainty in the
speed is the same for the two particles. The positions
of the two particles are also measured. Is the minimum
possible uncertainty in the electron’s position (a) less
than the minimum possible uncertainty in the proton’s
position, (b) the same as that for the proton, (c) more
than that for the proton, or (d) impossible to tell from
the given information?
Objective Questions
1. denotes answer available in Student Solutions Manual/Study Guide
1. (i) What is the principal quantum number of the initial
state of an atom as it emits an Mb line in an x-ray spectrum? (a) 1 (b) 2 (c) 3 (d) 4 (e) 5 (ii) What is the principal
quantum number of the final state for this transition?
Choose from the same possibilities as in part (i).
2. If an electron in an atom has the quantum numbers
n 5 3, , 5 2, m , 5 1, and m s 5 12, what state is it in?
(a) 3s (b) 3p (c) 3d (d) 4d (e) 3f
3. An electron in the n 5 5 energy level of hydrogen undergoes a transition to the n 5 3 energy level. What is the
wavelength of the photon the atom emits in this process?
(a) 2.28 3 1026 m (b) 8.20 3 1027 m (c) 3.64 3 1027 m
(d) 1.28 3 1026 m (e) 5.92 3 1025 m
4. Consider the n 5 3 energy level in a hydrogen atom.
How many electrons can be placed in this level? (a) 1
(b) 2 (c) 8 (d) 9 (e) 18
5. Which of the following is not one of the basic assumptions of the Bohr model of hydrogen? (a) Only certain
electron orbits are stable and allowed. (b) The electron
moves in circular orbits about the proton under the
influence of the Coulomb force. (c) The charge on
the electron is quantized. (d) Radiation is emitted by
the atom when the electron moves from a higher
energy state to a lower energy state. (e) The angular momentum associated with the electron’s orbital
motion is quantized.
6. Let 2E represent the energy of a hydrogen atom.
(i) What is the kinetic energy of the electron? (a) 2E
(b) E (c) 0 (d) 2E (e) 22E (ii) What is the potential
energy of the atom? Choose from the same possibilities
(a) through (e).
7. The periodic table is based on which of the following
principles? (a) The uncertainty principle. (b) All electrons in an atom must have the same set of quantum
numbers. (c) Energy is conserved in all interactions.
(d) All electrons in an atom are in orbitals having the
same energy. (e) No two electrons in an atom can have
the same set of quantum numbers.
8. (a) Can a hydrogen atom in the ground state absorb a
photon of energy less than 13.6 eV? (b) Can this atom
absorb a photon of energy greater than 13.6 eV?
9. Which of the following electronic configurations
are not allowed for an atom? Choose all correct
answers. (a) 2s 22p 6 (b) 3s 23p 7 (c) 3d 74s 2 (d) 3d 104s 24p 6
(e) 1s 22s 22d 1
10. What can be concluded about a hydrogen atom with
its electron in the d state? (a) The atom is ionized.
(b) The orbital quantum number is , 5 1. (c) The
principal quantum number is n 5 2. (d) The atom is in
its ground state. (e) The orbital angular momentum of
the atom is not zero.
11. (i) Rank the following transitions for a hydrogen atom
from the transition with the greatest gain in energy to
that with the greatest loss, showing any cases of equality. (a) n i 5 2; n f 5 5 (b) n i 5 5; n f 5 3 (c) n i 5 7; n f 5 4
(d) n i 5 4; n f 5 7 (ii) Rank the same transitions as in
part (i) according to the wavelength of the photon
absorbed or emitted by an otherwise isolated atom
from greatest wavelength to smallest.
12. When an atom emits a photon, what happens? (a) One
of its electrons leaves the atom. (b) The atom moves to
a state of higher energy. (c) The atom moves to a state
of lower energy. (d) One of its electrons collides with
another particle. (e) None of those events occur.
13. (a) In the hydrogen atom, can the quantum number n
increase without limit? (b) Can the frequency of possible discrete lines in the spectrum of hydrogen increase
without limit? (c) Can the wavelength of possible discrete lines in the spectrum of hydrogen increase without limit?
14. Consider the quantum numbers (a) n, (b) ,, (c) m ,,
and (d) ms . (i) Which of these quantum numbers are
fractional as opposed to being integers? (ii) Which can
sometimes attain negative values? (iii) Which can be
zero?
15. When an electron collides with an atom, it can transfer all or some of its energy to the atom. A hydrogen
atom is in its ground state. Incident on the atom are
several electrons, each having a kinetic energy of
10.5 eV. What is the result? (a) The atom can be excited
to a higher allowed state. (b) The atom is ionized.
(c) The electrons pass by the atom without interaction.
Objective Questions
1. denotes answer available in Student Solutions Manual/Study Guide
1. In nuclear magnetic resonance, suppose we increase
the value of the constant magnetic field. As a result,
the frequency of the photons that are absorbed in a
particular transition changes. How is the frequency of
the photons absorbed related to the magnetic field?
(a) The frequency is proportional to the square of
the magnetic field. (b) The frequency is directly proportional to the magnetic field. (c) The frequency is
independent of the magnetic field. (d) The frequency
is inversely proportional to the magnetic field. (e) The
frequency is proportional to the reciprocal of the
square of the magnetic field.
2. When the 95
36Kr nucleus undergoes beta decay by emitting an electron and an antineutrino, does the daughter
nucleus (Rb) contain (a) 58 neutrons and 37 protons,
(b) 58 protons and 37 neutrons, (c) 54 neutrons and 41
protons, or (d) 55 neutrons and 40 protons?
32
3. When 32
15P decays to 16 S, which of the following particles
is emitted? (a) a proton (b) an alpha particle (c) an
electron (d) a gamma ray (e) an antineutrino
sample H. (i) How does the half-life of G compare with
the half-life of H? (a) It is two times larger. (b) It is the
same. (c) It is half as large. (ii) After each has passed
through five half-lives, how do their activities compare? (a) G has more than twice the activity of H. (b) G
has twice the activity of H. (c) G and H have the same
activity. (d) G has lower activity than H.
6. If a radioactive nuclide AZ X decays by emitting a gamma
ray, what happens? (a) The resulting nuclide has a
different Z value. (b) The resulting nuclide has the
same A and Z values. (c) The resulting nuclide has a
different A value. (d) Both A and Z decrease by one.
(e) None of those statements is correct.
7. Does a nucleus designated as 40
18 X contain (a) 20 neutrons and 20 protons, (b) 22 protons and 18 neutrons,
(c) 18 protons and 22 neutrons, (d) 18 protons and 40
neutrons, or (e) 40 protons and 18 neutrons?
140
8. When 144
60Nd decays to 58Ce, identify the particle that
is released. (a) a proton (b) an alpha particle (c) an
electron (d) a neutron (e) a neutrino
4. The half-life of radium-224 is about 3.6 days. What
approximate fraction of a sample remains undecayed
after two weeks? (a) 12 (b) 14 (c) 18 (d) 161 (e) 321
9. What is the Q value for the reaction 9Be 1 a S 12C 1 n?
(a) 8.4 MeV (b) 7.3 MeV (c) 6.2 MeV (d) 5.7 MeV
(e) 4.2 MeV
5. Two samples of the same radioactive nuclide are
prepared. Sample G has twice the initial activity of
10. (i) To predict the behavior of a nucleus in a fission
reaction, which model would be more appropriate,
(a) the liquid-drop model or (b) the shell model?
(ii) Which model would be more successful in predicting the magnetic moment of a given nucleus?
Choose from the same answers as in part (i).
(iii) Which could better explain the gamma-ray spectrum of an excited nucleus? Choose from the same
answers as in part (i).
11. A free neutron has a half-life of 614 s. It undergoes
beta decay by emitting an electron. Can a free proton undergo a similar decay? (a) yes, the same decay
(b) yes, but by emitting a positron (c) yes, but with a
very different half-life (d) no
12. Which of the following quantities represents the reaction energy of a nuclear reaction? (a) (final mass 2 initial mass)/c 2 (b) (initial mass 2 final mass)/c 2 (c) (final
mass 2 initial mass)c 2 (d) (initial mass 2 final mass)c 2
(e) none of those quantities
A
4
13. In the decay 234
90Th S Z Ra 1 2He, identify the mass
number and the atomic number of the Ra nucleus:
(a) A 5 230, Z 5 92 (b) A 5 238, Z 5 88 (c) A 5 230,
Z 5 88 (d) A 5 234, Z 5 88 (e) A 5 238, Z 5 86