Download Chapter 30: Quantum Physics Chapter 31: Atomic Physics Chapter

Chapter 30: Quantum Physics
Answers to Even-Numbered Conceptual Questions
2.
If energy is quantized, as suggested by Planck, the amount of energy for even a single high-frequency photon can be
arbitrarily large. The finite energy in a blackbody simply can’t produce such high-frequency photons, and therefore the
infinite energy implied by the “ultraviolet catastrophe” cannot occur. In classical physics, any amount of energy can be
in the form of high-frequency light—the energy does not have to be supplied in discrete, large lumps as in Planck’s
theory. Therefore, classical physics implies that all frequencies of light have the same amount of energy, no matter how
high the frequency. This is what leads to the “catastrophe.”
4.
Planck’s theory of blackbody radiation implies a one-to-one relationship between the absolute temperature of a
blackbody and the frequency of light at the peak of its radiated energy spectrum. This relationship is given by Wien’s
displacement law (Equation 30-1). Therefore, by measuring the peak in the radiated energy from a star, we can tell its
temperature. In broad terms, a blue star is very hot, a red star much less so, and a yellowish star like our Sun is
intermediate in temperature.
6.
A monochromatic source of light means—literally—that it emits light of a single color. This means that all the photons
emitted by the source have the same frequency, and hence they also have the same energy.
8.
Classically, it should be possible to eject electrons with light of any frequency—all that is required is to increase the
intensity of the beam of light sufficiently. The fact that this is not the case means that the classical picture is incorrect.
In addition, the fact that there is a lowest frequency that will eject electrons implies that the energy of the photon is
proportional to its frequency, in agreement with E = hƒ.
10.
Yes. An electron and a proton have the same de Broglie wavelength    h p  if they have the same momentum.
Chapter 31: Atomic Physics
Answers to Even-Numbered Conceptual Questions
2.
(a) The glass tube of a neon sign contains a low-pressure gas. Therefore, we expect the light from the sign to be in the
form of a line spectrum. (b) The light from an incandescent lightbulb is basically blackbody radiation from a hot object;
therefore, its radiation is distributed continuously as a function of frequency.
4.
No, there is no upper limit to the radius of a Bohr orbit. In fact, the radius increases as n 2 for n  1, 2, 3,...
6.
No, the energy does not increase without limit. The energy of a given level in hydrogen ranges from a low of
13.6 eV to a maximum of zero.
8.
(a) The angular momentum in the quantum mechanical model of the hydrogen atom is zero if the quantum number is
zero. In the n  1 state, the only allowed value for is 0, and hence the orbital angular momentum must be zero for
n  1. (b) Yes. For n  1, there are n allowed values for the number . One of these values is always zero, therefore
the orbital angular momentum can be zero for any value of n .
Chapter 32: Nuclear Physics and Nuclear Radiation
Answers to Even-Numbered Conceptual Questions
2.
No. An alpha particle contains two protons, whereas any form of hydrogen contains only a single proton. Therefore,
hydrogen cannot give off an alpha particle.
4.
A change in isotope is simply a change in the number of neutrons in a nucleus. The electrons in the atom, however,
respond only to the protons with their positive charge. Because electrons are responsible for chemical reactions, it
follows that chemical properties are generally unaffected by a change in isotope.
6.
The obsidian arrowhead cannot be dated with carbon-14, because it is not of biological origin.
8.
Yes. If the different isotopes have different decay rates—which is generally the case—they can still have the same
activity if they are present in different amounts.
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