Chapter Assumptions
When converting between electron-volts and joules, assume that
1 eV = 1.60×10–19 J
Chapter 36 Problems
Conceptual Problems
C.1 One estimate for the number of grains of sand on all the beaches on Earth is 5×10^21 or five thousand billion billion grains.
Making the simplifying assumption that sand grains are uniform, give examples where the weight of an amount of sand can be
measured without considering the quantized nature of the sand, and cases where this cannot be ignored.C.2 Suppose two different hydrogen atoms, labeled A and B, have their electrons in state n = 4. Atom A emits light when its
electron transitions directly from the n = 4 state to the n = 2 state. Atom B emits light twice, as its electron first transitions from
the n = 4 state to the n = 3 state, then transitions from the n = 3 state to the n = 2 state. (a) Are the three wavelengths of light
the same or different? (b) How does the energy of the photon from atom A compare to the total energy of the two photons
from atom B?
(a) i. The wavelengths are the same
ii. The wavelengths are different
iii. Not enough information to tell
(b) i. The energies are equal
ii. The energies are different
iii. Not enough information to tellC.3 Suppose that for a particular metal, the photoelectric effect occurs with light of wavelength Ȝ 0. With this light incident on a
small region of metal, measurements show that electrons leaving the surface have kinetic energies as large as E 0. If the
intensity of light is increased without changing the wavelength, (a) how does this affect the number of electrons leaving the
surface? (b) What is the effect on the maximum kinetic energy of the ejected electrons?
(a) There are fewer electrons leaving the surface.
The number of electrons leaving the surface is unchanged.
There are more electrons leaving the surface.
(b) The electrons' maximum kinetic energy is less than E 0.
The electrons' maximum kinetic energy is still equal to E 0.
The electrons' maximum kinetic energy is greater than E 0.
C.4 In a p-type semiconductor, a current can flow when an electric field is applied and the following happens:
i. There is movement of holes in the valence band.
ii. There is movement of electrons in the valence band.
iii. There is movement of holes in the conduction band.
iv. There is movement of electrons in the conduction band.
C.5 In a p-n junction, can a hole cross from the p side to the n side without an electron crossing the junction from the n side to the
p side? Explain your answer.
Yes No
C.6 In your own words, explain why current does not readily flow in a circuit loop with a diode that is back-biased.C.7 Two doped semiconductors, one n-type and the other p-type, are brought together to form a p-n junction. Before being placed
in contact, they are each electrically neutral. They are brought into contact, and reach equilibrium (that is, the diffusion current
stops). (a) Is the net charge on the n-type semiconductor positive or negative? (b) Is the net charge on the p-type
semiconductor positive or negative?
(a) Positive Negative
(a) Positive Negative
C.8 Light is amplified in a laser. Consider photons with characteristics that are specific to the laser medium, that is, the laser will
emit light at the frequency of the photons. What property of these photons initially increases during the amplification process?
i. Wavelength
ii. Number of photons
iii. Energy of each photon
iv. Frequency