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Unit 5 - Practice Quiz

PHY110 50 Questions
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1 In the classical free electron theory, the electrons in a metal are assumed to behave like:

A. Fixed lattice points
B. Gas molecules in a container
C. Planetary objects orbiting a nucleus
D. Waves in a medium

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

A. It cannot explain Ohm's Law.
B. It fails to explain the electrical conductivity of metals.
C. It incorrectly predicts the specific heat and paramagnetic susceptibility of metals.
D. It cannot explain thermal conductivity.

3 The Drift Velocity () of electrons is related to the applied electric field () and mobility () by the equation:

A.
B.
C.
D.

4 Current generated due to the non-uniform concentration of charge carriers in a semiconductor is known as:

A. Drift current
B. Diffusion current
C. Displacement current
D. Leakage current

5 The Einstein relation connects the diffusion coefficient () and mobility () as (where is Boltzmann constant):

A.
B.
C.
D.

6 The Fermi-Dirac distribution function represents:

A. The energy of an electron in the valence band.
B. The probability that an energy state is occupied by an electron at temperature .
C. The density of states at energy .
D. The number of holes in the conduction band.

7 At absolute zero temperature ( K), the value of the Fermi-Dirac distribution function for is:

A. 0
B. 0.5
C. 1
D. Infinity

8 What is the probability of finding an electron at the Fermi energy level () for any temperature K?

A. 0
B. 1
C. 0.5
D. It depends on the material

9 The formation of allowed and forbidden energy bands in solids is primarily due to:

A. Electron-electron repulsion
B. The periodic potential of the crystal lattice
C. The high temperature of the solid
D. The finite size of the crystal

10 In the concept of Effective Mass, if an electron is near the top of a valence band, its effective mass () is:

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

11 The effective mass of an electron is related to the curvature of the E-k diagram by:

A.
B.
C.
D.

12 The Hall Effect is used to determine which of the following?

A. Band gap energy only
B. Type of charge carrier (n or p) and carrier concentration
C. Fermi energy level at 0K
D. Crystal structure of the material

13 In the derivation of the Hall Effect, the Hall electric field () balances which force?

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

14 The Hall Coefficient () is given by the formula (where is electron density):

A.
B.
C.
D.

15 For an Intrinsic Semiconductor, the Fermi level lies:

A. Inside the conduction band
B. Inside the valence band
C. Exactly in the middle of the forbidden energy gap (at T=0K)
D. Close to the conduction band

16 What happens to the Fermi level in an N-type semiconductor as the temperature increases significantly?

A. It moves closer to the conduction band.
B. It moves into the valence band.
C. It moves towards the center of the energy gap (intrinsic level).
D. It remains stationary.

17 In a P-type semiconductor, the Fermi level at absolute zero is located:

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

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

A. Gallium Arsenide (GaAs)
B. Silicon (Si)
C. Cadmium Sulfide (CdS)
D. Zinc Oxide (ZnO)

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

A. Mostly heat (phonons)
B. Mostly light (photons)
C. Mechanical vibration
D. Magnetic fields

20 The basic principle of a Solar Cell is:

A. Photo-emissive effect
B. Photovoltaic effect
C. Thermoelectric effect
D. Piezoelectric effect

21 In the Kronig-Penney model, if the potential barrier strength , the electron behaves as:

A. A bound electron
B. A free electron
C. A hole
D. An insulator

22 The unit of Mobility () is:

A.
B.
C.
D.

23 Which statistics are followed by free electrons in a metal?

A. Maxwell-Boltzmann statistics
B. Bose-Einstein statistics
C. Fermi-Dirac statistics
D. Planck's radiation law

24 The density of energy states for free electrons in 3 dimensions is proportional to:

A.
B.
C.
D.

25 In an insulator, the forbidden energy gap () is typically:

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

26 The Relaxation Time () of an electron is:

A. The time taken to cross the conductor.
B. The average time between two successive collisions.
C. The time to drift from negative to positive terminal.
D. The time taken to emit a photon.

27 A semiconductor doped with pentavalent impurity atoms (like Phosphorus) becomes:

A. P-type semiconductor
B. N-type semiconductor
C. Intrinsic semiconductor
D. Superconductor

28 The electrical conductivity () of a semiconductor is given by:

A.
B.
C.
D.

29 In the Hall Effect experiment, if the Hall voltage is measured across the width of a specimen kept in a magnetic field , the Hall field is:

A.
B.
C.
D.

30 Which parameter determines the Fill Factor of a solar cell?

A. The band gap energy only.
B. The ratio of maximum obtainable power to the product of open-circuit voltage and short-circuit current.
C. The thickness of the depletion region.
D. The refractive index of the coating.

31 For an indirect band gap semiconductor, a transition from Valence to Conduction band requires:

A. Only a photon
B. A photon and a phonon (lattice vibration)
C. Only thermal energy
D. A magnetic field

32 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. Band gap energy

33 What is the physical meaning of a Hole?

A. A proton moving in the lattice.
B. A positron generated by decay.
C. A vacancy created by a missing electron in the valence band acting as a positive charge.
D. An electron in the conduction band.

34 In the context of the Kronig-Penney model, as the barrier strength , the allowed energy bands:

A. Become continuous (free particle)
B. Disappear completely
C. Narrow down to discrete energy levels (atomic levels)
D. Overlap completely

35 The resistivity of an intrinsic semiconductor decreases with increasing temperature because:

A. Mobility decreases slightly.
B. Carrier concentration () increases exponentially.
C. Lattice vibrations increase.
D. Band gap increases.

36 The Law of Mass Action for a semiconductor in thermal equilibrium states:

A.
B.
C.
D.

37 In a Hall effect setup for a P-type semiconductor, the Hall voltage is generated because:

A. Electrons accumulate on one side.
B. Holes accumulate on one side due to the Lorentz force.
C. Ions move to the surface.
D. The magnetic field generates heat.

38 The region in a Solar Cell IV characteristic curve where the cell delivers power is:

A. First Quadrant
B. Second Quadrant
C. Third Quadrant
D. Fourth Quadrant

39 Which of the following describes the Drude-Lorentz model's assumption about electron interaction?

A. Electrons interact strongly with each other.
B. Electrons do not interact with each other or the ions (except during collisions).
C. Electrons are trapped in potential wells.
D. Electrons form Cooper pairs.

40 When an electric field is applied to a semiconductor, the total current density is the sum of:

A.
B.
C.
D.

41 The Fermi Energy () of a metal is typically in the range of:

A. 0.01 eV - 0.1 eV
B. 1 eV - 10 eV
C. 100 eV - 1 keV
D. MeV range

42 In the expression for Hall Voltage , the symbol represents:

A. Time
B. Temperature
C. Thickness of the sample
D. Torque

43 Which material is most commonly used for standard solar cells?

A. Copper
B. Silicon
C. Plastic
D. Aluminum

44 The effective mass of an electron is usually denoted by . The ratio (where is free electron mass) in a semiconductor can be:

A. Always equal to 1
B. Always greater than 1
C. Greater than, less than, or equal to 1
D. Always zero

45 The Short Circuit Current () of a solar cell corresponds to:

A. Voltage = 0
B. Current = 0
C. Maximum Power Point
D. Infinite Resistance

46 The Open Circuit Voltage () of a solar cell occurs when:

A. The circuit is closed.
B. Current is zero.
C. Maximum power is drawn.
D. It is kept in the dark.

47 For , if , the Fermi-Dirac distribution approaches:

A. Bose-Einstein statistics
B. Maxwell-Boltzmann statistics
C. 1
D. 0.5

48 The diffusion current density for holes () is proportional to:

A. Electric Field
B. Concentration gradient
C. Hall Voltage
D. Temperature

49 Why are indirect band gap semiconductors (like Si) generally poor light emitters?

A. They have no electrons.
B. Recombination requires a phonon, making the radiative process slow and inefficient compared to non-radiative recombination.
C. Their band gap is too large.
D. They absorb light too quickly.

50 In the Kronig-Penney model, the term (scattering power of the potential barrier) is defined as:

A.
B.
C.
D.
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