Electronics Lecture 5 - MCQs and Essay Questions
Multiple-Choice Questions (MCQs)
1. What is the Band Theory of Solids primarily based on?
A. Overlapping atomic orbitals
B. Random movement of electrons
C. Fixed discrete energy levels
D. Magnetic field effects
2. What is the purpose of the valence band?
A. It contains electrons that can participate in conduction
B. It stores excess charge
C. It reflects light in metals
D. It acts as an insulator under all conditions
3. Which statement is true about conduction bands?
A. It contains free electrons responsible for electrical conduction
B. It is always full of electrons
C. It prevents current flow
D. It is only present in insulators
4. The forbidden energy gap is:
A. The energy difference between valence and conduction bands
B. The highest energy level occupied by electrons
C. The energy required to remove an electron from an atom
D. The resistance of a material to current flow
5. Conductors have:
A. Overlapping valence and conduction bands
B. A very large band gap
C. No free electrons
D. No electrical conductivity
6. Why do insulators not conduct electricity under normal conditions?
A. The forbidden energy gap is very large
B. They have too many free electrons
C. The valence band is empty
D. Their atoms do not vibrate
7. What happens to a conductor when its temperature increases?
A. Its resistance increases
B. It becomes a better conductor
C. Its forbidden energy gap increases
D. Electrons stop moving
8. A semiconductor at absolute zero behaves like:
A. An insulator
B. A conductor
C. A metal
D. A superconductor
9. The electrical conductivity of semiconductors:
A. Increases with temperature
B. Decreases with temperature
C. Remains constant
D. Is unpredictable
10. Silicon and Germanium are examples of:
A. Intrinsic semiconductors
B. Conductors
C. Insulators
D. Superconductors
11. What distinguishes an intrinsic semiconductor from an extrinsic one?
A. It does not contain impurities
B. It has a smaller band gap
C. It has better conductivity
D. It does not respond to temperature changes
12. What is the primary characteristic of an n-type semiconductor?
A. It has excess electrons
B. It has more holes than electrons
C. It has no charge carriers
D. It behaves like an insulator
13. What is the primary characteristic of a p-type semiconductor?
A. It has excess holes
B. It has more electrons than holes
C. It has no conductivity
D. It has a negative charge
14. What type of impurity is added to create an n-type semiconductor?
A. Pentavalent
B. Trivalent
C. Monovalent
D. Divalent
15. What type of impurity is added to create a p-type semiconductor?
A. Trivalent
B. Pentavalent
C. Monovalent
D. Hexavalent
16. What happens in an intrinsic semiconductor when an electron jumps to the conduction band?
A. A hole is created in the valence band
B. The material becomes an insulator
C. The energy gap disappears
D. The electrons stop moving
17. Which material has the smallest energy gap?
A. Germanium
B. Silicon
C. Diamond
D. Copper
18. The energy gap in silicon is approximately:
A. 1.21 eV
B. 0.5 eV
C. 2.3 eV
D. 4.2 eV
19. The energy gap in germanium is approximately:
A. 0.785 eV
B. 1.21 eV
C. 2.8 eV
D. 5 eV
20. Doping is a process used to:
A. Improve conductivity of semiconductors
B. Increase resistance
C. Make conductors behave like insulators
D. Increase the band gap
21. The conductivity of an intrinsic semiconductor is mainly due to:
A. Thermally excited electron-hole pairs
B. The presence of free electrons from impurities
C. The overlapping of bands
D. Magnetic field effects
22. What happens to the resistance of a semiconductor as temperature increases?
A. It decreases
B. It increases
C. It remains constant
D. It fluctuates randomly
23. What type of charge carrier is responsible for conduction in p-type semiconductors?
A. Holes
B. Electrons
C. Neutrons
D. Protons
24. In n-type semiconductors, conduction is primarily due to:
A. Electrons
B. Holes
C. Positive ions
D. Neutrons
25. What type of bond exists between atoms in a silicon crystal?
A. Covalent
B. Ionic
C. Metallic
D. Van der Waals
26. What happens when a silicon atom is doped with phosphorus?
A. Extra free electrons are introduced
B. The silicon becomes a p-type semiconductor
C. The silicon becomes an insulator
D. The band gap increases
27. What is the role of holes in a p-type semiconductor?
A. They act as positive charge carriers
B. They block conduction
C. They are fixed in place
D. They repel electrons
28. Which material has the highest energy gap?
A. Diamond
B. Silicon
C. Germanium
D. Copper
29. What is the process of adding impurities to a semiconductor called?
A. Doping
B. Ionization
C. Polarization
D. Insulation
30. Which of the following is NOT a semiconductor?
A. Copper
B. Silicon
C. Germanium
D. Gallium arsenide
Essay Questions
1. Explain the concept of the Band Theory of Solids and its importance in electronics.
2. Describe the differences between conductors, insulators, and semiconductors.
3. Explain how temperature affects the conductivity of semiconductors.
4. Discuss the process of doping and its effect on semiconductor behavior.
5. Compare the properties of intrinsic and extrinsic semiconductors.
6. How does the band gap determine whether a material is a conductor, insulator, or
semiconductor?
7. Explain how electron-hole pairs are generated in intrinsic semiconductors.
8. Describe the characteristics of p-type and n-type semiconductors and their applications.
9. Explain why silicon is more widely used than germanium in semiconductor devices.
10. Discuss the impact of band gap size on the electrical properties of materials.
