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Unit 5 - Practice Quiz

PHY110

1 In the classical free electron theory, the valence electrons in a metal are treated as:

A. Fixed particles attached to nuclei
B. A gas of free molecules moving randomly
C. Quantum mechanical wave packets
D. Particles moving in a periodic potential

2 What is the primary failure of the classical free electron theory (Drude-Lorentz theory)?

A. It could not explain Ohm's Law
B. It could not explain electrical conductivity
C. It predicted incorrect values for specific heat and heat capacity of metals
D. It failed to explain thermal conductivity

3 The Fermi energy () is defined as:

A. The minimum energy possessed by an electron at 0 K
B. The energy of the lowest occupied level at 0 K
C. The energy of the highest occupied quantum state at 0 K
D. The average energy of electrons at room temperature

4 According to the Fermi-Dirac distribution function, what is the probability of occupation of an energy state at any temperature ?

A.
B. 1
C. 0.5
D. Undefined

5 Which of the following expressions represents the Fermi-Dirac distribution function?

A.
B.
C.
D.

6 Drift current in a semiconductor is caused by:

A. Concentration gradient of charge carriers
B. Application of an external electric field
C. Temperature gradient
D. Magnetic field application

7 Diffusion current in a semiconductor flows from:

A. Lower concentration to higher concentration
B. Higher potential to lower potential
C. Higher concentration to lower concentration
D. Lower potential to higher potential

8 The relation between the diffusion coefficient () and mobility () is given by the Einstein relation:

A.
B.
C.
D.

9 In the band theory of solids, the formation of energy bands is primarily due to:

A. Electron-electron repulsion
B. Pauli exclusion principle and interaction of atoms in a crystal lattice
C. External magnetic fields
D. High temperature effects

10 The energy gap () represents:

A. The energy difference between the top of the conduction band and bottom of the valence band
B. The energy difference between the bottom of the conduction band and the top of the valence band
C. The width of the conduction band
D. The ionization energy of the atom

11 Which of the following characterizes an insulator?

A. Partially filled conduction band
B. Overlapping valence and conduction bands
C. Large forbidden energy gap ( eV)
D. Zero forbidden energy gap

12 The effective mass () of an electron in a solid is related to the curvature of the curve by:

A.
B.
C.
D.

13 If the curvature of the band () is negative near the top of the valence band, the effective mass is:

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

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

A. A proton moving in the lattice
B. A positron
C. A vacancy created by a missing electron in the valence band
D. An electron in the conduction band

15 The Hall Effect is observed when a current-carrying conductor is placed in:

A. A transverse electric field
B. A transverse magnetic field
C. A parallel magnetic field
D. A vacuum chamber

16 The Hall Coefficient () is defined mathematically as:

A.
B.
C.
D.

17 For an n-type semiconductor, the Hall coefficient is:

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

18 The formula for Hall coefficient in terms of carrier concentration is:

A.
B.
C.
D.

19 Which of the following parameters cannot be determined directly using the Hall Effect?

A. Type of semiconductor (n-type or p-type)
B. Carrier concentration
C. Mobility of charge carriers
D. Band gap energy

20 In the derivation of the Hall voltage , the Hall field exerts a force that balances the:

A. Gravitational force
B. Lorentz magnetic force
C. Nuclear force
D. Friction force

21 If the Hall voltage is , width of the specimen is , and thickness is , the Hall field is:

A.
B.
C.
D.

22 An intrinsic semiconductor at 0 K behaves as:

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

23 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 Conduction Band

24 When a pentavalent impurity is added to pure silicon, the resulting semiconductor is:

A. P-type
B. N-type
C. Intrinsic
D. Insulating

25 In an N-type semiconductor, the donor energy level is located:

A. Just above the valence band
B. Just below the conduction band
C. In the middle of the energy gap
D. Inside the conduction band

26 In a P-type semiconductor, the Fermi level moves:

A. Towards the conduction band
B. Towards the valence band
C. Remains at the center
D. Into the conduction band

27 The Law of Mass Action for semiconductors states that at equilibrium:

A.
B.
C.
D.

28 As the temperature of an extrinsic semiconductor increases significantly, the Fermi level:

A. Moves closer to the respective band edge
B. Moves towards the center of the energy gap (intrinsic level)
C. Does not change
D. Disappears

29 The total conductivity () of a semiconductor is given by:

A.
B.
C.
D.

30 What is the primary difference between Direct and Indirect band gap semiconductors?

A. The width of the band gap
B. The alignment of the minimum of conduction band and maximum of valence band in k-space
C. The density of states
D. The type of doping used

31 In a Direct Band Gap semiconductor, electron recombination results primarily in:

A. Emission of heat (phonons)
B. Emission of light (photons)
C. Generation of magnetic fields
D. Crystal vibration only

32 Which of the following is an example of an Indirect Band Gap semiconductor?

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

33 Why is Silicon not used for making LEDs?

A. It is too expensive
B. It has a direct band gap
C. It has an indirect band gap, leading to energy loss as heat
D. It melts at low temperatures

34 The basic principle of a Solar Cell is:

A. Photoconductive effect
B. Photovoltaic effect
C. Photoemissive effect
D. Thermionic emission

35 The I-V characteristic of a solar cell is typically drawn in which quadrant?

A. First quadrant (Power dissipation)
B. Second quadrant
C. Third quadrant
D. Fourth quadrant (Power generation)

36 The 'Fill Factor' of a solar cell represents:

A. The ratio of open circuit voltage to short circuit current
B. The ratio of maximum obtainable power to the product of open circuit voltage and short circuit current
C. The efficiency of light absorption
D. The thickness of the depletion region

37 In the Fermi-Dirac distribution, if and , then is:

A.
B. 1
C. 0.5
D. Infinite

38 The density of states for free electrons in a 3D metal is proportional to:

A.
B.
C.
D.

39 Which velocity is associated with the random motion of electrons at Fermi level?

A. Drift velocity
B. Fermi velocity
C. Phase velocity
D. Group velocity

40 In a p-n junction solar cell, electron-hole pairs are generated primarily in:

A. The metal contacts
B. The depletion region (space charge region)
C. The neutral n-region only
D. The neutral p-region only

41 The efficiency of a solar cell is defined as:

A. Output Current / Input Current
B. Max Electrical Power Output / Optical Power Input
C. Voltage Output / Light Intensity
D. Fill Factor Temperature

42 For a p-type semiconductor, the concentration of holes () relates to the acceptor concentration () approximately as:

A.
B.
C.
D.

43 The mean free path of an electron is:

A. The average time between collisions
B. The average distance traveled between two successive collisions
C. The total distance traveled in one second
D. The distance between the nucleus and the electron

44 Mobility () of a charge carrier is defined as:

A. Velocity per unit electric field
B. Force per unit charge
C. Current per unit area
D. Acceleration per unit time

45 The unit of Hall coefficient () is:

A.
B.
C.
D.

46 What happens to the resistivity of a semiconductor as temperature increases?

A. It increases linearly
B. It increases exponentially
C. It decreases
D. It remains constant

47 In the Kronig-Penney model (origin of bands), the potential is approximated as:

A. A constant zero potential
B. A simple harmonic oscillator potential
C. A periodic array of rectangular potential wells/barriers
D. A Coulomb potential

48 Which material is commonly used as a dopant to create P-type Silicon?

A. Phosphorus (P)
B. Arsenic (As)
C. Boron (B)
D. Antimony (Sb)

49 The open-circuit voltage () of a solar cell:

A. Increases with temperature
B. Decreases with temperature
C. Is independent of temperature
D. Is zero at room temperature

50 If the effective mass of an electron is usually denoted , and the free electron mass is , in most semiconductors:

A. always
B. can be smaller or larger than
C. is always zero
D. is imaginary