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Physic
Q:
A nucleus with a mass number of 64 has a mean radius of about:A) 4.8 fmB) 9.6fmC) 77 fmD) 260 fmE) 2.6 x105fm
Q:
Volumes of atomic nuclei are proportional to:
A) the mass number
B) the atomic number
C) the total nuclear spin
D) the number of neutrons
E) none of these
Q:
The mass density of an atomic nucleus:
A) is about 1015kg/m3
B) is about 1012kg/m3
C) increases with increasing nuclear mass
D) increases with decreasing nuclear radius
E) is roughly constant independent of atomic number
Q:
Which of the following nuclides is least stable?
A) 52Fe (Z= 26)
B) 115Nd (Z= 60)
C) 175Lu (Z= 71)
D) 208Pb (Z= 82)
E) 238U (Z= 92)
Q:
Let A be the mass number andZbe the atomic number of a nucleus. Which of the following is approximately correct for light nuclei?
A) Z= 2A
B) Z= A
C) Z= A/2
D) Z=
E) Z= A2
Q:
Stable nuclei generally:
A) have a greater number of protons than neutrons
B) have low mass numbers
C) have high mass numbers
D) are beta emitters
E) none of the above
Q:
Bromine, with atomic mass 79.942 u, is composed of nearly equal amounts of two isotopes, one of which contains 79 nucleons per atom. The mass number of the other isotope is:
A) 78
B) 79
C) 80
D) 81
E) 82
Q:
The isotopes of an element:
A) cannot be separated at all
B) occur well separated in nature
C) have similar chemical behavior
D) cannot be separated by physical methods
E) have equal masses
Q:
Let Zdenote the atomic number and Adenote the mass number of a nucleus. The number of neutrons in this nucleus is:A) ZB) A- ZC) A- 2ZD) AE) 2A- Z
Q:
Iron has atomic number 26. Naturally mined iron contains isotopes of mass numbers 54, 56, 57, and 58. Which of the following statements is FALSE?
A) every atom of iron has 26 protons
B) some iron atoms have 30 neutrons
C) some iron atoms have 54 neutrons
D) the isotopes may be separated in a mass spectrometer
E) there are four kinds of naturally occurring iron atoms with the same chemical properties
Q:
The atomic number of an element is:
A) the whole number nearest to its mass
B) the number of protons in its nucleus
C) the nearest whole number of hydrogen atoms having the same mass as a single atom of the given element
D) the number of neutrons in its nucleus
E) its order of discovery
Q:
A femtometer is:A) larger than 10-9mB) 10-9mC) 10-12mD) 10-15mE) 10-18m
Q:
The smallest particle of any chemical element that can exist by itself and yet retain the qualities that distinguish it as that element is:
A) an electron
B) a proton
C) a neutron
D) an atom
E) a molecule
Q:
In the Rutherford scattering experiment, an alpha particle is aimed directly at a gold nucleus. The distance of closest approach of the alpha particle to the nucleus occurs when:
A) the alpha particle hits the nucleus
B) the alpha particle hits the electron cloud
C) the kinetic energy of the alpha particle is completely transformed to potential energy due to the nuclear force
D) the kinetic energy of the alpha particle is completely transformed to potential energy due to the electric field of the nucleus
E) the kinetic energy of the alpha particle is completely transformed to potential energy due to the electric field of the electrons
Q:
The Rutherford scattering experiment showed that:
A) light has both particle-like and wavelike properties
B) atoms are electrically neutral
C) the positive and negative charges in the atom are uniformly distributed throughout its volume
D) the wavelength of scattered light depends on the scattering angle
E) the atom consists of a very tiny, massive, positively charged nucleus surrounded by almost empty space
Q:
The gap between the valence and conduction bands of a certain semiconductor is 0.85eV. When this semiconductor is used to form a light emitting diode, the wavelength of the light emitted:A) is in a range above 1.5 x10-6mB) is in a range below 1.5 x10-6mC) is always 1.5 x10-6mD) is in a range centered on 1.5 x10-6mE) has nothing to do with the gap
Q:
A light emitting diode emits light when:
A) electrons are excited from the valence to the conduction band
B) electrons from the conduction band recombine with holes from the valence band
C) electrons collide with atoms
D) electrons are accelerated by the electric field in the depletion region
E) the junction gets hot
Q:
"LED" stands for:
A) Less Energy Donated
B) Light Emitting Degrader
C) Luminescent Energy Diode
D) Laser EmittingDevice
E) none of the above
Q:
Switch S is closed to apply a potential difference Vacross a p-njunction as shown. Relative to the energy levels of the n-type material, with the switch open, the electron levels of the p-type material are:A) unchangedB) lowered by the amount e-Ve/kTC) lowered by the amount VeD) raised by the amount e-Ve/kTE) raised by the amount Ve
Q:
Which of the following is NOT true when a back bias is applied to a p-njunction?
A) Electrons flow from the pto the nside
B) Holes flow from the pto the nside
C) The electric field in the depletion zone increases
D) The potential difference across the depletion zone increases
E) The depletion zone narrows
Q:
When a forward bias is applied to a p-njunction the concentration of electrons on the pside:
A) increases slightly
B) increases dramatically
C) decreases slightly
D) decreases dramatically
E) does not change
Q:
Application of a forward bias to a p-njunction:
A) increases the drift current in the depletion zone
B) increases the diffusion current in the depletion zone
C) decreases the drift current on the pside outside the depletion zone
D) decreases the drift current on the nside outside the depletion zone
E) does not change the current anywhere
Q:
Application of a forward bias to a p-njunction:
A) narrows the depletion zone
B) increases the electric field in the depletion zone
C) increases the potential difference across the depletion zone
D) increases the number of donors on the nside
E) decreases the number of donors on the nside
Q:
A sinusoidal potential difference is applied to the p-njunction as shown. Which graph correctly shows Voutas a function of time?A) IB) IIC) IIID) IVE) V
Q:
For an unbiased p-njunction, the energy at the bottom of the conduction band on the nside is:
A) higher than the energy at the bottom of the conduction band on the pside
B) lower than the energy at the bottom of the conduction band on the pside
C) lower than energy at the top of the valence band on the nside
D) lower than energy at the top of the valence band on the pside
E) the same as the energy at the bottom of the conduction band on the pside
Q:
In an unbiased p-njunction:
A) the electric potential vanishes everywhere
B) the electric field vanishes everywhere
C) the drift current vanishes everywhere
D) the diffusion current vanishes everywhere
E) the diffusion and drift currents cancel each other
Q:
The contact electric field in the depletion region of a p-njunction is produced by:
A) electrons in the conduction band alone
B) holes in the valence band alone
C) electrons and holes together
D) charged replacement atoms
E) an applied bias potential difference
Q:
A donor replacement atom in silicon might have ______ electrons in its outer shell.
A) 1
B) 2
C) 3
D) 4
E) 5
Q:
An acceptor replacement atom in silicon might have ______ electrons in its outer shell.
A) 3
B) 4
C) 5
D) 6
E) 7
Q:
Acceptor atoms introduced into a pure semiconductor at room temperature:
A) increase the number of electrons in the conduction band
B) increase the number of holes in the valence band
C) lower the Fermi level
D) increase the electrical resistivity
E) none of the above
Q:
Donor atoms introduced into a pure semiconductor at room temperature:
A) increase the number of electrons in the conduction band
B) increase the number of holes in the valence band
C) lower the Fermi level
D) increase the electrical resistivity
E) none of the above
Q:
Compared to the number of conduction electrons in pure silicon, the number of conduction electrons in doped silicon is:
A) lower by about a factor of 10
B) about the same
C) higher by about a factor of 10
D) higher by about a factor of 1000
E) higher by about a factor or 1,000,000
Q:
A given doped semiconductor can be identified as por ntype by:
A) measuring its electrical conductivity
B) measuring its magnetic susceptibility
C) measuring its coefficient of resistivity
D) measuring its heat capacity
E) performing a Hall effect experiment
Q:
For a pure semiconductor at room temperature the temperature coefficient of resistivity is determined primarily by:
A) the number of electrons in the conduction band
B) the number of replacement atoms
C) the binding energy of outer shell electrons
D) collisions between conduction electrons and atoms
E) none of the above
Q:
For a metal at room temperature the temperature coefficient of resistivity is determined primarily by:
A) the number of electrons in the conduction band
B) the number of impurity atoms
C) the binding energy of outer shell electrons
D) collisions between conduction electrons and atoms
E) none of the above
Q:
A hole refers to:
A) a proton
B) a positively charged electron
C) an electron which has somehow lost its charge
D) a microscopic defect in a solid
E) the absence of an electron in an otherwise filled band
Q:
Compared to an insulator, the energy gap of a semiconductor is:
A) much smaller
B) about the same
C) much larger
D) full of holes
E) full of charge carriers
Q:
For a pure semiconductor the Fermi level is:
A) in the conduction band
B) well above the conduction band
C) in the valence band
D) well below the valence band
E) near the center of the gap between the valence and conduction bands
Q:
The energy level diagram shown applies to: A) a conductor
B) an insulator
C) a semiconductor
D) an isolated molecule
E) an isolated atom
Q:
A pure semiconductor at room temperature has:
A) more electrons/m3in its conduction band than holes/m3in its valence band
B) more electrons/m3in its conduction band than a typical metal
C) more electrons/m3in its valence band than at T = 0 K
D) more holes/m3in its valence band than electrons/m3in its valence band
E) none of the above
Q:
Magnesium has 8.6 x 1028conduction electrons per cubic meter. What is the Fermi energy for magnesium?
A) 1.8 eV
B) 7.1 eV
C) 9.1 eV
D) 22 eV
E) 28 eV
Q:
If the density of states is N(E) and the occupancy probability is P(E), then the density of unoccupied states is:A) N(E) + P(E)B) N(E)/P(E)C) N(E) - P(E)D) N(E)P(E)E) N(E)(1 -> P(E))
Q:
The occupancy probability for a state with energy equal to the Fermi energy is:
A) 0
B) 0.5
C) 1
D) 1.5
E) 2
Q:
At room temperature, kTis about 0.0259 eV. The probability that a state 0.50 eV below the Fermi level is unoccupied at room temperature is:A) 1B) 0.05C) 0.026D) 5.0 x10-6E) 4.1 x10-9
Q:
At room temperature, kTis about 0.0259 eV. The probability that a state 0.50 eV above the Fermi level is occupied at room temperature is:A) 1B) 0.05C) 0.026D) 5.0 x10-6E) 4.1 x10-9
Q:
At T = 0 K the probability that a state 0.50 eV above the Fermi level is occupied is:A) 0B) 5.0 x10-9C) 5.0x10-6D) 5.0x10-3E) 1
Q:
At T = 0 K the probability that a state 0.50 eV below the Fermi level is occupied is:A) 0B) 5.0 x10-9C) 5.0 x10-6D) 5.0 x10-3E) 1
Q:
For a metal at absolute temperature T,with Fermi energy EF,the occupancy probability is given by:
A) B) C) D) E)
Q:
Possible units for the density of states function N(E) are:A) J/m3B) 1/JC) m-3D) J-1.m-3E) kg/m3
Q:
If Ïmis the mass density of a conducting material, Vits volume, Mits molar mass, and NAAvogadro's number, the number density nof conduction electrons in the material is given by:
A) B) C) D) E)
Q:
The speed of an electron with energy equal to the Fermi energy for copper is on the order of:A) 10-6 m/sB) 10-1 m/sC) 10 m/sD) 106 m/sE) 109m/s
Q:
In a metal at 0 K, the Fermi energy is:
A) the highest energy of any electron
B) the lowest energy of any electron
C) the mean thermal energy of the electrons
D) the energy of the top of the valence band
E) the energy at the bottom of the conduction band
Q:
The energy level diagram shown applies to: A) a conductor
B) an insulator
C) a semiconductor
D) an isolated molecule
E) an isolated atom
Q:
Electrons in a full band do not contribute to the current when an electric field exists in a solid because:
A) the field cannot exert a force on them
B) the individual contributions cancel each other
C) they are not moving
D) they make transitions to other bands
E) they leave the solid
Q:
The energy level diagram shown applies to: A) a conductor
B) an insulator
C) a semiconductor
D) an isolated atom
E) a free electron gas
Q:
The energy gap between the valence and conduction bands of an insulator is of the order:A) 10-19eVB) 0.001 eVC) 0.1 eVD) 10 eVE) 1000 eV
Q:
The Fermi energy of a metal depends primarily on:
A) the temperature
B) the volume of the sample
C) the mass density of the metal
D) the size of the sample
E) the number density of conduction electrons
Q:
The density of states for a metal depends primarily on:
A) the temperature
B) the energy associated with the state
C) the density of the metal
D) the volume of the sample
E) none of these
Q:
If E0and ETare the average energies of the "free" electrons in a metal at 0 K and room temperature respectively, then the ratio ET/E0is approximately:
A) 0
B) 1
C) 100
D) 106
E) infinity
Q:
Which one of the following statements concerning electron energy bands in solids is true?
A) the bands occur as a direct consequence of the Fermi-Dirac distribution function
B) electrical conduction arises from the motion of electrons in completely filled bands
C) within a given band, all electron energy levels are equal to each other
D) an insulator has a large energy separation between the highest filled band and the lowest empty band
E) only insulators have energy bands
Q:
A certain material has a resistivity of at room temperature, and its resistivity increases as the temperature is raised by 100ï‚°C. The material is most likely:A) a metalB) a pure semiconductorC) a heavily doped semiconductorD) an insulatorE) none of the above
Q:
A certain material has a resistivity of at room temperature, and its resistivity decreases as the temperature is raised by 100°C. The material is most likely:A) a metalB) a pure semiconductorC) a heavily doped semiconductorD) an insulatorE) none of the above
Q:
A certain material has a resistivity of at room temperature, and its resistivity increases as the temperature is raised by 100°C. The material is most likely:A) a metalB) a pure semiconductorC) a heavily doped semiconductorD) an insulatorE) none of the above
Q:
The number density n of conduction electrons, the resistivity , and the temperature coefficient of resistivity are given below for five materials. Which is a semiconductor?
Q:
We classify solids electrically according to three basic properties. What are they?
A) Conductivity, resistivity, and crystal structure
B) Resistivity, temperature coefficient of resistivity, and crystal structure
C) Resistivity, crystal structure, and number density of conduction electrons
D) Resistivity, temperature coefficient of resistivity, and number density of conduction electrons
E) Conductivity, temperature coefficient of resistivity, and crystal structure
Q:
The Fermi-Dirac probability function P(E) varies between:A) 0 and 1B) 0 and infinityC) 1 and infinityD) -1 and 1E) 0 and EF
Q:
If electrons did not have intrinsic angular momentum (spin) but still obeyed the Pauli exclusion principle the states occupied by electrons in the ground state of helium would be:A) (n= 1, =0); (n= 1, =0)B) (n= 1, =0); (n= 1, =1)C) (n= 1, =0); (n= 2, =0)D) (n= 2, =0); (n= 2, =1)E) (n= 2, =1); (n= 2, =1)
Q:
Which of the following subshells cannot exist?
A) 3p
B) 2p
C) 4d
D) 3d
E) 2d
Q:
The ionization energy of an atom in its ground state is:A) the energy required to remove the least energetic electronB) the energy required to remove the most energetic electronC) the energy difference between the most energetic electron and the least energetic electronD) the same as the energy of a photonE) the same as the excitation energy of the most energetic electron
Q:
The group of atoms at the beginning of periods of the periodic table is called:
A) alkali metal atoms
B) rare earth atoms
C) transition metal atoms
D) alkaline atoms
E) noble gas atoms
Q:
The group of atoms at the ends of periods of the periodic table is called:
A) alkali metal atoms
B) rare earth atoms
C) transition metal atoms
D) alkaline atoms
E) noble gas atoms
Q:
The most energetic electron in any atom at the end of a period of the periodic table is in:A) an =0 stateB) an =1 stateC) an =2 stateD) an n= 0 state with unspecified angular momentumE) an n= 1 state with unspecified angular momentum
Q:
The most energetic electron in any atom at the beginning of a period of the periodic table is in:A) an =0 stateB) an =1 stateC) an =2 stateD) an n= 0 state with unspecified angular momentumE) an n= 1 state with unspecified angular momentum
Q:
When a lithium atom is made from a helium atom by adding a proton (and neutron) to the nucleus and an electron outside, the electron goes into an n= 2, =0 state rather than an n= 1, =0 state. This is an indication that electrons:A) obey the Pauli exclusion principleB) obey the minimum energy principleC) undergo the Zeeman effectD) are diffractedE) and protons are interchangeable
Q:
Six electrons are in a two-dimensional square potential energy well with sides of length L. The potential energy is infinite at the sides and zero inside. The single-particle energies are given by where nxand nyare integers. If a seventh electron is added to the system when it is in its ground state the least energy the additional electron can have is:
A) 2(h2/8mL2)
B) 5(h2/8mL2)
C) 8 (h2/8mL2)
D) 10 (h2/8mL2)
E) 13 (h2/8mL2)
Q:
Electrons are in a two-dimensional square potential energy well with sides of length L. The potential energy is infinite at the sides and zero inside. The single-particle energies are given by where nxand nyare integers. The number of single-particle states with energy 5(h2/8mL2) is:
A) 1
B) 2
C) 3
D) 4
E) 5
Q:
Five electrons are in a two-dimensional square potential energy well with sides of length L. The potential energy is infinite at the sides and zero inside. The single-particle energies are given by where nxand nyare integers. The energy of the first excited state of the system is:
A) 13 (h2/8mL2)
B) 22 (h2/8mL2)
C) 24 (h2/8mL2)
D) 25 (h2/8mL2)
E) 27 (h2/8mL2)
Q:
Five electrons are in a two-dimensional square potential energy well with sides of length L. The potential energy is infinite at the sides and zero inside. The single-particle energies are given by where nxand nyare integers. The energy of the ground state of the system is
A) 0
B) 10 (h2/8mL2)
C) 19 (h2/8mL2)
D) 24 (h2/8mL2)
E) 48 (h2/8mL2)
Q:
Electrons are in a two-dimensional square potential energy well with sides of length L. The potential energy is infinite at the sides and zero inside. The single-particle energies are given by , ,where nxand nyare integers. At most the number of electrons that can have energy 8(h2/8mL2) is:
A) 1
B) 2
C) 3
D) 4
E) any number
Q:
No state in an atom can be occupied by more than one electron. This is most closely related to the:
A) wave nature of matter
B) finite value for the speed of light
C) Bohr magneton
D) Pauli exclusion principle
E) the Einstein-de Haas effect