Question 1

Which one of the following statements concerning electron energy bands in solids is true?

Accepted Answer

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 
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

Question 2

The Fermi-Dirac probability function P(E) varies between:

Accepted Answer

A)  0 and 1 
B)  0 and infinity 
C)  1 and infinity 
D)  -1 and 1 
E)  0 and EF  
A)  0 and 1 
B)  0 and infinity 
C)  1 and infinity 
D)  -1 and 1 
E)  0 and EF

Question 3

Which of the following is NOT true when a back bias is applied to a p-n junction?

Accepted Answer

A)  Electrons flow from the p to the n side 
B)  Holes flow from the p to the n side 
C)  The electric field in the depletion zone increases 
D)  The potential difference across the depletion zone increases 
E)  The depletion zone narrows 
A)  Electrons flow from the p to the n side 
B)  Holes flow from the p to the n side 
C)  The electric field in the depletion zone increases 
D)  The potential difference across the depletion zone increases 
E)  The depletion zone narrows

Question 4

The energy gap (in eV) between the valence and conduction bands of an insulator is of the order:

Accepted Answer

A)  10-19 
B)  0.001 
C)  0.1 
D)  10 
E)  1000 
A)  10-19 
B)  0.001 
C)  0.1 
D)  10 
E)  1000

Question 5

At room temperature kT is about 0.0259 eV. The probability that a state 0.50 eV above the Fermi level is occupied at room temperature is:

Accepted Answer

A)  1 
B)  0.05 
C)  0.025 
D)  5.0 * 10-6 
E)  4.1 *10-9 
A)  1 
B)  0.05 
C)  0.025 
D)  5.0 * 10-6 
E)  4.1 *10-9

Question 6

The contact electric field in the depletion region of a p-n junction is produced by:

Accepted Answer

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 
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

Question 7

For a pure semiconductor the Fermi level is:

Accepted Answer

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 
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

Question 8

A light emitting diode emits light when:

Accepted Answer

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 
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

Question 9

Ther Fermi energy of a metal depends primarily on:

Accepted Answer

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 
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

Question 10

The energy level diagram shown applies to:

Accepted Answer

A)  a conductor 
B)  an insulator 
C)  a semiconductor 
D)  an isolated atom 
E)  a free electron gas 
A)  a conductor 
B)  an insulator 
C)  a semiconductor 
D)  an isolated atom 
E)  a free electron gas

Question 11

The density of states for a metal depends primarily on:

Accepted Answer

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 
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

Question 12

A certain material has a resistivity of 7.8* 103 $\Omega$.m at room temperature and it increases as the temperature is raised by 100$\degree$C. The material is most likely:

Accepted Answer

A)  a metal 
B)  a pure semiconductor 
C)  a heavily doped semiconductor 
D)  an insulator 
E)  none of the above 
A)  a metal 
B)  a pure semiconductor 
C)  a heavily doped semiconductor 
D)  an insulator 
E)  none of the above

Question 13

In an unbiased p-n junction:

Accepted Answer

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 
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

Question 14

For a pure semiconductor at room temperature the temperature coefficient of resistivity is determined primarily by:

Accepted Answer

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 
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

Question 15

For a metal at room temperature the temperature coefficient of resistivity is determined primarily by:

Accepted Answer

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 
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

Question 16

Application of a forward bias to a p-n junction:

Accepted Answer

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 p side outside the depletion zone 
D)  decreases the drift current on the n side outside the depletion zone 
E)  does not change the current anywhere 
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 p side outside the depletion zone 
D)  decreases the drift current on the n side outside the depletion zone 
E)  does not change the current anywhere

Question 17

Electrons in a full band do not contribute to the current when an electric field exists in a solid because:

Accepted Answer

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 
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

Question 18

If E0 and ET are the average energies of the "free" electrons in a metal at 0 K and room temperature respectively, then the ratio ET/E0 is approximately:

Accepted Answer

A)  0 
B)  1 
C)  100 
D)  106 
E)  infinity 
A)  0 
B)  1 
C)  100 
D)  106 
E)  infinity

Question 19

A sinusoidal potential difference Vin = Vmsin($ \omega $t) is applied to the p-n junction as shown. Which graph correctly shows Vout as a function of time?

Accepted Answer

A)  I 
B)  II 
C)  III 
D)  IV 
E)  V 
A)  I 
B)  II 
C)  III 
D)  IV 
E)  V

Question 20

In a metal at 0 K, the Fermi energy is:

Accepted Answer

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 
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

Exam 41: Conduction of Electricity in Solids

Which one of the following statements concerning electron energy bands in solids is true?

The Fermi-Dirac probability function P(E) varies between:

Which of the following is NOT true when a back bias is applied to a p-n junction?

The energy gap (in eV) between the valence and conduction bands of an insulator is of the order:

At room temperature kT is about 0.0259 eV. The probability that a state 0.50 eV above the Fermi level is occupied at room temperature is:

The contact electric field in the depletion region of a p-n junction is produced by:

For a pure semiconductor the Fermi level is:

A light emitting diode emits light when:

Ther Fermi energy of a metal depends primarily on:

The energy level diagram shown applies to:

The density of states for a metal depends primarily on:

A certain material has a resistivity of 7.8* 103 Ω\OmegaΩ .m at room temperature and it increases as the temperature is raised by 100 °\degree° C. The material is most likely:

In an unbiased p-n junction:

For a pure semiconductor at room temperature the temperature coefficient of resistivity is determined primarily by:

For a metal at room temperature the temperature coefficient of resistivity is determined primarily by:

Application of a forward bias to a p-n junction:

Electrons in a full band do not contribute to the current when an electric field exists in a solid because:

If E0 and ET are the average energies of the "free" electrons in a metal at 0 K and room temperature respectively, then the ratio ET/E0 is approximately:

A sinusoidal potential difference Vin = Vmsin( ω \omega ω t) is applied to the p-n junction as shown. Which graph correctly shows Vout as a function of time?

In a metal at 0 K, the Fermi energy is:

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A certain material has a resistivity of 7.8* 10³ $\Omega$ .m at room temperature and it increases as the temperature is raised by 100 $\degree$ C. The material is most likely:

If E₀ and E_T are the average energies of the "free" electrons in a metal at 0 K and room temperature respectively, then the ratio E_T/E₀ is approximately: