Question 1

Compared to the number of conduction electrons in pure silicon, the number of conduction electrons in doped silicon is:

Accepted Answer

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 
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

Question 2

Compared to an insulator, the energy gap of a semiconductor is:

Accepted Answer

A) much smaller 
B) about the same 
C) much larger 
D) full of holes 
E) full of charge carriers 
A) much smaller 
B) about the same 
C) much larger 
D) full of holes 
E) full of charge carriers

Question 3

If ρm is the mass density of a conducting material, V its volume, M its molar mass, and NA Avogadro's number, the number density n of conduction electrons in the material is given by:

Accepted Answer

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

Question 4

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 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) 0.026 
D) 5.0* 10-6 
E) 4.1 *10-9 
A) 1 
B) 0.05 
C) 0.026 
D) 5.0* 10-6 
E) 4.1 *10-9

Question 6

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 7

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 8

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 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 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 11

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 12

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 13

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 14

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

Question 15

Switch S is closed to apply a potential difference V across a p-n junction 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:

Accepted Answer

A) unchanged 
B) lowered by the amount e-Ve/kT 
C) lowered by the amount Ve 
D) raised by the amount e-Ve/kT 
E) raised by the amount Ve 
A) unchanged 
B) lowered by the amount e-Ve/kT 
C) lowered by the amount Ve 
D) raised by the amount e-Ve/kT 
E) raised by the amount Ve

Question 16

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) 0.026 
D) 5.0 * 10-6 
E) 4.1 *10-9 
A) 1 
B) 0.05 
C) 0.026 
D) 5.0 * 10-6 
E) 4.1 *10-9

Question 17

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 18

For an unbiased p-n junction, the energy at the bottom of the conduction band on the n side is:

Accepted Answer

A) higher than the energy at the bottom of the conduction band on the p side 
B) lower than the energy at the bottom of the conduction band on the p side 
C) lower than energy at the top of the valence band on the n side 
D) lower than energy at the top of the valence band on the p side 
E) the same as the energy at the bottom of the conduction band on the p side 
A) higher than the energy at the bottom of the conduction band on the p side 
B) lower than the energy at the bottom of the conduction band on the p side 
C) lower than energy at the top of the valence band on the n side 
D) lower than energy at the top of the valence band on the p side 
E) the same as the energy at the bottom of the conduction band on the p side

Question 19

At T = 0 K the probability that a state 0.50 eV above 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 20

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

Exam 41: Conduction of Electricity in Solids

Compared to the number of conduction electrons in pure silicon, the number of conduction electrons in doped silicon is:

Compared to an insulator, the energy gap of a semiconductor is:

If ρm is the mass density of a conducting material, V its volume, M its molar mass, and NA Avogadro's number, the number density n of conduction electrons in the material is given by:

For a pure semiconductor the Fermi level is:

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:

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

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

The density of states for a metal depends primarily on:

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

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

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

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:

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

Switch S is closed to apply a potential difference V across a p-n junction 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:

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:

In an unbiased p-n junction:

For an unbiased p-n junction, the energy at the bottom of the conduction band on the n side is:

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

The energy level diagram shown applies to:

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If ρ_m is the mass density of a conducting material, V its volume, M its molar mass, and N_A Avogadro's number, the number density n of conduction electrons in the material is given by:

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: