Back to Subject
View Notes

Unit 5 - Practice Quiz

PHY109

1 In the classical free electron theory, the electrons in a metal are assumed to behave like:

A. A solid crystal lattice
B. A perfect gas molecules
C. Liquid molecules
D. Bound atomic electrons

2 Which of the following is a drawback of the Classical Free Electron Theory?

A. It cannot explain Ohm's Law
B. It fails to explain the electrical conductivity
C. It fails to explain the specific heat capacity and paramagnetic susceptibility
D. It implies that electrons are stationary

3 The drift velocity is related to the applied electric field and mobility by the relation:

A.
B.
C.
D.

4 Diffusion current in a semiconductor is caused by:

A. Applied electric field
B. Applied magnetic field
C. Concentration gradient of charge carriers
D. Temperature difference only

5 The Einstein relation relating the diffusion coefficient and mobility is given by:

A.
B.
C.
D.

6 The Fermi energy () of a metal at 0 K is defined as:

A. The average energy of electrons
B. The energy of the lowest occupied state
C. The maximum energy possessed by an electron at 0 K
D. The minimum energy required to remove an electron

7 The Fermi-Dirac distribution function represents:

A. The density of energy states
B. The probability of occupancy of an energy state
C. The energy gap between bands
D. The number of electrons per unit volume

8 Mathematically, the Fermi-Dirac distribution function is given by:

A.
B.
C.
D.

9 At temperature K, what is the probability of occupancy of the Fermi energy level ()?

A.
B. 1
C. 0.5
D. Undefined

10 The density of states for free electrons in a three-dimensional metal is proportional to:

A.
B.
C.
D.

11 According to the Band Theory of Solids, the energy gap () in an insulator is approximately:

A. Zero
B. Less than 1 eV
C. Greater than 3 eV
D. Exactly 0.7 eV

12 In a conductor (metal), the valence band and conduction band:

A. Are separated by a large gap
B. Are separated by a small gap
C. Overlap with each other
D. Are both empty

13 At 0 K, a pure intrinsic semiconductor behaves as:

A. A perfect conductor
B. A perfect insulator
C. A superconductor
D. A semiconductor with high conductivity

14 The position of the Fermi level in an intrinsic semiconductor at absolute zero is located:

A. Inside the conduction band
B. Inside the valence band
C. Exactly in the middle of the forbidden energy gap
D. Near the bottom of the conduction band

15 In an N-type semiconductor, the Fermi level at 0 K lies:

A. In the middle of the energy gap
B. Near the bottom of the conduction band
C. Near the top of the valence band
D. Inside the valence band

16 In a P-type semiconductor, the impurity atoms added are called:

A. Donors
B. Acceptors
C. Intrinsic
D. Phonons

17 As temperature increases, the Fermi level in an N-type semiconductor:

A. Moves closer to the conduction band
B. Moves towards the middle of the energy gap
C. Moves into the valence band
D. Remains constant

18 Which of the following represents the Law of Mass Action for semiconductors?

A.
B.
C.
D.

19 A Direct Band Gap semiconductor is one where:

A. The maximum of the valence band and minimum of the conduction band occur at different values of wave vector
B. The maximum of the valence band and minimum of the conduction band occur at the same value of wave vector
C. There is no energy gap
D. Conduction is only due to holes

20 An example of an Indirect Band Gap semiconductor is:

A. Gallium Arsenide (GaAs)
B. Silicon (Si)
C. Indium Phosphide (InP)
D. Cadmium Sulfide (CdS)

21 Recombination of an electron and hole in a Direct Band Gap semiconductor results primarily in:

A. Emission of heat (phonons)
B. Emission of light (photons)
C. Change in crystal structure
D. Zero energy release

22 The concept of Effective Mass () accounts for:

A. The relativistic change in mass
B. The interaction of the electron with the periodic potential of the crystal lattice
C. The weight of the electron due to gravity
D. The mass of the nucleus

23 Mathematically, the effective mass is related to the energy-wave vector () curvature by:

A.
B.
C.
D.

24 Near the top of the valence band, the effective mass of an electron is:

A. Positive
B. Negative
C. Zero
D. Infinite

25 A 'hole' in solid state physics is best described as:

A. A proton moving in the lattice
B. A positron
C. An empty state in an otherwise filled valence band behaving like a positive charge
D. A neutron

26 The Hall Effect is the production of a voltage difference across an electrical conductor, transverse to an electric current and to an applied:

A. Electric field parallel to current
B. Magnetic field perpendicular to the current
C. Thermal gradient
D. Gravitational field

27 The Hall coefficient is given by the relation:

A.
B.
C.
D.

28 If the Hall coefficient is negative, the majority charge carriers are:

A. Holes
B. Electrons
C. Neutrons
D. Ions

29 The Hall voltage generated in a slab of thickness , carrying current in a magnetic field , is:

A.
B.
C.
D.

30 Which of the following is NOT an application of the Hall Effect?

A. Determination of semiconductor type (N or P)
B. Measurement of magnetic field strength (Fluxmeter)
C. Measurement of carrier concentration
D. Measuring the refractive index of the material

31 The Hall angle is the angle between:

A. The magnetic field and the current
B. The electric field and the magnetic field
C. The resultant electric field and the current density direction
D. The crystal axis and current

32 The Fermi temperature is related to Fermi energy by:

A.
B.
C.
D.

33 In the derivation of Hall effect, at equilibrium, the magnetic Lorentz force () is balanced by:

A. Gravitational force
B. Electric force due to Hall field ()
C. Frictional force
D. Nuclear force

34 The mobility of holes () is generally _____ than the mobility of electrons () in the same semiconductor.

A. Greater
B. Less
C. Equal
D. Unrelated

35 For an intrinsic semiconductor, the Hall coefficient is:

A. Zero
B. Very large positive
C. Very large negative
D. Ideally small, decreasing with temperature

36 The Wiedemann-Franz law states that the ratio of thermal conductivity () to electrical conductivity () is proportional to:

A. Temperature ()
B. Inverse of Temperature ()
C. Temperature squared ()
D. Ideally constant

37 The unit of Hall coefficient is:

A.
B.
C.
D.

38 If the effective mass of an electron is small, the curvature of the energy band is:

A. Small (flat band)
B. Large (steep curve)
C. Zero
D. Undefined

39 Which statistics are applicable to electrons in a solid?

A. Maxwell-Boltzmann
B. Bose-Einstein
C. Fermi-Dirac
D. Plank's Radiation Law

40 The Fermi level in a P-type semiconductor at room temperature is:

A. Closer to the valence band
B. Closer to the conduction band
C. At the center of the gap
D. Above the conduction band

41 The probability that an energy level is occupied by a hole is given by:

A.
B.
C.
D.

42 In the free electron gas model, the potential energy of an electron inside the metal is assumed to be:

A. Infinite
B. Periodic
C. Constant
D. Zero everywhere including boundaries

43 The mean free path of an electron is defined as:

A. The average distance traveled between two successive collisions
B. The total distance traveled in one second
C. The distance from the nucleus to the surface
D. The wavelength of the electron

44 Electrical conductivity () is given by:

A.
B.
C.
D.

45 Which material is typically used for making LEDs?

A. Silicon (Si)
B. Germanium (Ge)
C. Gallium Arsenide (GaAs)
D. Carbon (C)

46 At absolute zero, the electrical conductivity of a pure metal is:

A. Zero
B. Infinite (or extremely high)
C. Same as at room temperature
D. Negative

47 The total current density in a semiconductor is the sum of:

A. Electron drift and Hole drift only
B. Electron diffusion and Hole diffusion only
C. Drift current densities and Diffusion current densities for both electrons and holes
D. Conduction current and displacement current

48 The value of Fermi function ranges from:

A. 0 to
B. -1 to +1
C. 0 to 1
D. 1 to 100

49 In a p-type semiconductor, the minority carriers are:

A. Holes
B. Electrons
C. Positive Ions
D. Acceptor atoms

50 The dependence of Fermi energy on electron density in a metal at 0 K is:

A.
B.
C.
D.