Questions: 5, 13
Problems: 6, 8, 26, 31
Questions: 3
Problems: 11, 13
Q29.5: A laser emits a beam of light whose photons all have the same frequency. When the beam strikes the surface of a metal, photoelectrons are ejected from the surface.
What happens if the laser emits twice the number of photons per second? (a) The photoelectrons are ejected from the surface with twice the maximum kinetic energy. (b)
The photoelectrons are ejected from the surface with the same maximum kinetic energy.
(c) The number of photoelectrons ejected per second from the surface doubles. (d) Both b and c happen. (e) Both a and c happen.
Q29.13: Two particles, A and B, have the same mass, but particle A has a charge of 1q and B has a charge of 12q. The particles are accelerated from rest through the same potential difference. Which one has the longer de Broglie wavelength at the end of the acceleration? (a) Particle A, because it has the greater momentum, and, hence, the longer de Broglie wavelength (b) Particle B, because it has the greater momentum, and, hence, the longer de Broglie wavelength (c) Particle A, because it has the smaller momentum, and, hence, the longer de Broglie wavelength (d) Particle B, because it has the smaller momentum, and, hence, the longer de Broglie wavelength (e) Both particles have the same de Broglie wavelength.
P29.6: The maximum wavelength that an electromagnetic wave can have and still eject electrons from a metal surface is 485 nm. What is the work function W0 of this metal?
Express your answer in electron volts.
Answer : 2.56 eV
P29.8: Radiation with a wavelength of 238 nm shines on a metal surface and ejects electrons that have a maximum speed of 3.75 3 105 m/s. Which one of the following metals is it, the values in parentheses being the work functions: potassium (2.24 eV), calcium (2.71 eV), uranium (3.63 eV), aluminum (4.08 eV), or gold (4.82 eV)?
Answer : gold
P29.26: What are (a) the wavelength of a 5.0-eV photon and (b) the de Broglie wavelength of a 5.0-eV electron?
Answer : 2.5
× 10 -7 m, 5.6
× 10 -10 m
P29.31: A particle has a de Broglie wavelength of 2.7
× 10 -10 m. Then its kinetic energy doubles. What is the particle’s new de Broglie wave- length, assuming that relativistic effects can be ignored? Answer : 1.9
× 10 -10 m
Q30.3: According to the Bohr model, what determines the shortest wavelength in a given series of wavelengths emitted by the atom? (a) The quantum number n i
that identifies the higher energy level from which the electron falls into a lower energy level (b) The quantum number n f
that identifies the lower energy level into which the electron falls from a higher energy level (c) The ratio n f
/n i
, where nf is the quantum number that
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identifies the lower energy level into which the electron falls and n i
is the quantum number that identifies the higher level from which the electron falls (d) The sum n f
+ n i
of two quantum numbers, where n f
identifies the lower energy level into which the electron falls and n i
identifies the higher level from which the electron falls (e) The difference n f
− n i
of two quantum numbers, where n f
identifies the lower energy level into which the electron falls and n i
identifies the higher level from which the electron falls
P30.11: Find the energy (in joules) of the photon that is emitted when the electron in a hydrogen atom undergoes a transition from the n 5 7 energy level to produce a line in the Paschen series. Answer : 1.98
× 10 -19 J (or 1.23 eV)
P30.13: A particle has a de Broglie wavelength of 2.7
× 10 -10 m. Then its kinetic energy doubles. What is the particle’s new de Broglie wave- length, assuming that relativistic effects can be ignored? Answer : 656 nm, 122 nm
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