Question 1

An acceptor replacement atom in silicon might have ______ electrons in its outer shell.

Accepted Answer

A) 3 
B) 4 
C) 5 
D) 6 
E) 7 
A) 3 
B) 4 
C) 5 
D) 6 
E) 7 A

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 B

Question 3

A given doped semiconductor can be identified as p or n type by:

Accepted Answer

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 
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 E

Question 4

The number density n of conduction electrons, the resistivity $\rho$, and the temperature coefficient of resistivity α are given below for five materials.Which is a semiconductor?

Accepted Answer

A) n = 1029 m-3, $\rho$= 10-8  $\Omega$. m, α = +10-3 K-1 
B) n = 1028 m-3, $\rho$= 10-9  $\Omega$. m, α = -10-3 K-1 
C) n = 1028 m-3, $\rho$= 10-9  $\Omega$. m, α = +10-3 K-1 
D) n = 1015 m-3, $\rho$= 103  $\Omega$. m, α = -10-2 K-1 
E) n = 1022 m-3, $\rho$ = 10-7 $\Omega$. m, α = +10-3 K-1 
A) n = 1029 m-3, $\rho$= 10-8  $\Omega$. m, α = +10-3 K-1 
B) n = 1028 m-3, $\rho$= 10-9  $\Omega$. m, α = -10-3 K-1 
C) n = 1028 m-3, $\rho$= 10-9  $\Omega$. m, α = +10-3 K-1 
D) n = 1015 m-3, $\rho$= 103  $\Omega$. m, α = -10-2 K-1 
E) n = 1022 m-3, $\rho$ = 10-7 $\Omega$. m, α = +10-3 K-1

Question 5

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) N(
E) (1 − P(
E) ) 
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) )

Question 6

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:

Accepted Answer

A) is in a range above 1.5 * 10-6 m 
B) is in a range below 1.5 * 10-6 m 
C) is always 1.5 * 10-6 m 
D) is in a range centered on 1.5 *10-6 m 
E) has nothing to do with the gap 
A) is in a range above 1.5 * 10-6 m 
B) is in a range below 1.5 * 10-6 m 
C) is always 1.5 * 10-6 m 
D) is in a range centered on 1.5 *10-6 m 
E) has nothing to do with the gap

Question 7

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

Accepted Answer

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 n side 
E) decreases the number of donors on the n side 
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 n side 
E) decreases the number of donors on the n side

Question 8

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 9

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

Accepted Answer

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

Question 10

A pure semiconductor at room temperature has:

Accepted Answer

A) more electrons/m3 in its conduction band than holes/m3 in its valence band 
B) more electrons/m3 in its conduction band than a typical metal 
C) more electrons/m3 in its valence band than at T = 0 K 
D) more holes/m3 in its valence band than electrons/m3 in its valence band 
E) none of the above 
A) more electrons/m3 in its conduction band than holes/m3 in its valence band 
B) more electrons/m3 in its conduction band than a typical metal 
C) more electrons/m3 in its valence band than at T = 0 K 
D) more holes/m3 in its valence band than electrons/m3 in its valence band 
E) none of the above

Question 11

Magnesium has 8.6 x 1028 conduction electrons per cubic meter.What is the Fermi energy for magnesium?

Accepted Answer

A) 1.8 eV 
B) 7.1 eV 
C) 9.1 eV 
D) 22 eV 
E) 28 eV 
A) 1.8 eV 
B) 7.1 eV 
C) 9.1 eV 
D) 22 eV 
E) 28 eV

Question 12

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 13

The 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 14

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 15

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 16

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 17

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 18

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 19

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 20

A certain material has a resistivity of 7.8 * 10-8  $\Omega$ .m at room temperature, and its resistivity 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

Exam 41: Conduction of Electricity in Solids

An acceptor replacement atom in silicon might have ______ electrons in its outer shell.

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 given doped semiconductor can be identified as p or n type by:

The number density n of conduction electrons, the resistivity ρ\rhoρ , and the temperature coefficient of resistivity α are given below for five materials.Which is a semiconductor?

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

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:

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

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:

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

A pure semiconductor at room temperature has:

Magnesium has 8.6 x 1028 conduction electrons per cubic meter.What is the Fermi energy for magnesium?

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

The Fermi energy of a metal depends primarily on:

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

The energy level diagram shown applies to:

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

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

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

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

A certain material has a resistivity of 7.8 * 10-8 Ω\OmegaΩ .m at room temperature, and its resistivity increases as the temperature is raised by 100 °\degree° C.The material is most likely:

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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:

The number density n of conduction electrons, the resistivity $\rho$ , and the temperature coefficient of resistivity α are given below for five materials.Which is a semiconductor?

Magnesium has 8.6 x 10²⁸ conduction electrons per cubic meter.What is the Fermi energy for magnesium?

A certain material has a resistivity of 7.8 * 10^-8 $\Omega$ .m at room temperature, and its resistivity increases as the temperature is raised by 100 $\degree$ C.The material is most likely: