Question 1

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 B

Question 2

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 C

Question 3

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 E

Question 4

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 5

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

Question 6

The occupancy probability for a state with energy equal to the Fermi energy is:

Accepted Answer

A)  0 
B)  0.5 
C)  1 
D)  1.5 
E)  2 
A)  0 
B)  0.5 
C)  1 
D)  1.5 
E)  2

Question 7

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 8

A certain material has a resistivity of 7.8 *10-8 $\Omega$ .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 9

A hole refers to:

Accepted Answer

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 
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

Question 10

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 11

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 12

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 13

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

Accepted Answer

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

Question 14

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 15

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 16

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

Question 17

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 18

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 19

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 20

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

Exam 41: Conduction of Electricity in Solids

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

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:

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 an unbiased p-n junction:

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

The occupancy probability for a state with energy equal to the Fermi energy is:

The energy level diagram shown applies to:

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

A hole refers to:

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 light emitting diode emits light when:

A pure semiconductor at room temperature has:

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

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:

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

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

The density of states for a metal depends primarily on:

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

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

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:

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

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

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: