Question 1

If the density of states is N(E) and the occupancy probability is P(E), then the density of unoccupied states is:

Accepted Answer

A)  N(
E)  + P(
E)  
B)  N(
E) /P(
E)  
C)  N(
E)  - P(
E)  
D)  N(
E) P(
E)  
E)  P(
E) /N(
E)  
A)  N(
E)  + P(
E)  
B)  N(
E) /P(
E)  
C)  N(
E)  - P(
E)  
D)  N(
E) P(
E)  
E)  P(
E) /N(
E)

Question 2

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 3

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 4

The energy level diagram shown applies to:

Accepted Answer

A)  a conductor 
B)  an insulator 
C)  a semiconductor 
D)  an isolated molecule 
E)  an isolated atom 
A)  a conductor 
B)  an insulator 
C)  a semiconductor 
D)  an isolated molecule 
E)  an isolated atom

Question 5

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 6

At room temperature kT is about 0.0259 eV. The probability that a state 0.50 eV below the Fermi level is unoccupied 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 7

A donor replacement atom in silicon might have ______ electrons in its outer shell.

Accepted Answer

A)  1 
B)  2 
C)  3 
D)  4 
E)  5 
A)  1 
B)  2 
C)  3 
D)  4 
E)  5

Question 8

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 9

At T = 0 K the probability that a state 0.50 eV below the Fermi level is occupied is:

Accepted Answer

A)  0 
B)  5.0* 10-9 
C)  5.0* 10-6 
D)  5.0 * 10-3 
E)  1 
A)  0 
B)  5.0* 10-9 
C)  5.0* 10-6 
D)  5.0 * 10-3 
E)  1

Question 10

For a metal at absolute temperature T, with Fermi energy EF, the occupancy probability is given by:

Accepted Answer

A)    
B)    
C)    
D)    
E)    
A)    
B)    
C)    
D)    
E)

Question 11

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 12

The speed of an electron with energy equal to the Fermi energy for copper is on ther order of:

Accepted Answer

A)  106 m/s 
B)  10-6 m/s 
C)  10 m/s 
D)  10-1 m/s 
E)  109 m/s 
A)  106 m/s 
B)  10-6 m/s 
C)  10 m/s 
D)  10-1 m/s 
E)  109 m/s

Question 13

"LED" stands for:

Accepted Answer

A)  Less Energy Donated 
B)  Light Energy Degrader 
C)  Luminescent Energy Developer 
D)  Laser Energy Detonator 
E)  none of the above 
A)  Less Energy Donated 
B)  Light Energy Degrader 
C)  Luminescent Energy Developer 
D)  Laser Energy Detonator 
E)  none of the above

Question 14

Possible units for the density of states function N(E) are:

Accepted Answer

A)  J/m3 
B)  1/J 
C)  m-3 
D)  J-1. m-3 
E)  kg/m3 
A)  J/m3 
B)  1/J 
C)  m-3 
D)  J-1. m-3 
E)  kg/m3

Question 15

In a pure metal the collisions that are characterized by the mean free time  $ \tau $ in the expression for the resistivity are chiefly between:

Accepted Answer

A)  electrons and other electrons 
B)  electrons with energy about equal to the Fermi energy and atoms 
C)  all electrons and atoms 
D)  electrons with energy much less than the Fermi energy and atoms 
E)  atoms and other atoms 
A)  electrons and other electrons 
B)  electrons with energy about equal to the Fermi energy and atoms 
C)  all electrons and atoms 
D)  electrons with energy much less than the Fermi energy and atoms 
E)  atoms and other atoms

Question 16

A certain material has a resistivity of 7.8 *103  $\Omega$  . m at room temperature and it decreases 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 17

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 18

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 19

A certain metal has 5.3 *1029 conduction electrons/m3 and an electrical resistivity of 1.9 * 10-9 $\Omega$.m.The average time between collisions of electrons with atoms in the metal is:

Accepted Answer

A)  5.6 * 10-33 s 
B)  1.3 *10-31 s 
C)  9.9 * 10-22 s 
D)  4.6*10-15 s 
E)  3.5* 10-14 s 
A)  5.6 * 10-33 s 
B)  1.3 *10-31 s 
C)  9.9 * 10-22 s 
D)  4.6*10-15 s 
E)  3.5* 10-14 s

Question 20

When a forward bias is applied to a p-n junction the concentration of electrons on the p side:

Accepted Answer

A)  increases slightly 
B)  increases dramatically 
C)  decreases slightly 
D)  decreases dramatically 
E)  does not change 
A)  increases slightly 
B)  increases dramatically 
C)  decreases slightly 
D)  decreases dramatically 
E)  does not change

Exam 41: Conduction of Electricity in Solids

If the density of states is N(E) and the occupancy probability is P(E), then the density of unoccupied states is:

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:

For a pure semiconductor the Fermi level is:

The energy level diagram shown applies to:

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 below the Fermi level is unoccupied at room temperature is:

A donor replacement atom in silicon might have ______ electrons in its outer shell.

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

At T = 0 K the probability that a state 0.50 eV below the Fermi level is occupied is:

For a metal at absolute temperature T, with Fermi energy EF, the occupancy probability is given by:

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

The speed of an electron with energy equal to the Fermi energy for copper is on ther order of:

"LED" stands for:

Possible units for the density of states function N(E) are:

In a pure metal the collisions that are characterized by the mean free time τ \tau τ in the expression for the resistivity are chiefly between:

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

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

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

A certain metal has 5.3 *1029 conduction electrons/m3 and an electrical resistivity of 1.9 * 10-9 Ω\OmegaΩ .m.The average time between collisions of electrons with atoms in the metal is:

When a forward bias is applied to a p-n junction the concentration of electrons on the p side:

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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:

For a metal at absolute temperature T, with Fermi energy E_F, the occupancy probability is given by:

In a pure metal the collisions that are characterized by the mean free time $\tau$ in the expression for the resistivity are chiefly between:

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

A certain metal has 5.3 10²⁹ conduction electrons/m³ and an electrical resistivity of 1.9 10^-⁹ $\Omega$ .m.The average time between collisions of electrons with atoms in the metal is: