All Free Electrical Engineering MCQs with Answers

• A. Controlled switch
• B. Bidirectional switch
• C. Unidirectional switch
• D. None of the above

Explanation: A pn junction conducts readily in forward bias but blocks current in reverse bias, so it behaves like a unidirectional switch.

• A. Equals the number of holes
• B. Is greater than the number of holes
• C. Is less than the number of holes
• D. None of the above

Explanation: In an intrinsic semiconductor, electron-hole pairs are generated together, so every free electron is accompanied by a hole.

• A. Junction capacitance
• B. Minority carriers
• C. Majority carriers
• D. None of the above

Explanation: With increasing temperature, thermally generated minority carriers increase markedly, while the majority-carrier concentration in an…

• A. Aa
• B. mA
• C. kA
• D. µA

Explanation: Reverse leakage current in an ordinary pn junction is very small, typically in the microampere range.

• A. Minority carriers
• B. Majority carriers
• C. Junction capacitance
• D. None of the above

Explanation: Under reverse bias, minority carriers are swept across the depletion region and produce the small leakage or reverse saturation current.

• A. Decreases
• B. Increases
• C. Remains the same
• D. None of the above

Explanation: Forward bias opposes the junction’s built-in electric field, reducing the barrier potential and narrowing the depletion layer.

• A. Many holes only
• B. A few free electrons and holes
• C. Many free electrons only
• D. No holes or free electrons

Explanation: An intrinsic semiconductor has equal numbers of thermally generated free electrons and holes; at room temperature their concentration is…

• A. A battery
• B. A conductor
• C. An insulator
• D. A piece of copper wire

Explanation: Pure silicon has very few free charge carriers at room temperature, so its conductivity is low and it behaves approximately as an…

• A. O
• B. kO
• C. MO
• D. None of the above

Explanation: Forward bias lowers the diode barrier and allows substantial current, so its dynamic or forward resistance is small, typically of the…

• A. Only holes
• B. Only free electrons
• C. Holes and free electrons
• D. None of the above

Explanation: Semiconductor current is the sum of electron current and hole current. Their relative contributions depend on whether the material is…

• A. 10 atoms for 108 atoms
• B. 1 atom for 108 atoms
• C. 1 atom for 104 atoms
• D. 1 atom for 100 atoms

Explanation: Only a very small fraction of atoms is replaced by impurity atoms in an extrinsic semiconductor, commonly about one impurity atom per 10^8…

• A. 6 x 10^4 cm
• B. 60 x cm
• C. 3 x 10^6 cm
• D. 6 x 10^-4 cm

Explanation: Pure germanium has a resistivity of approximately 60 Ω·cm under ordinary standard conditions.

• A. 3
• B. 5
• C. 4
• D. 6

Explanation: A pentavalent impurity has five electrons in its outer shell. Four participate in covalent bonds with the semiconductor, leaving one extra…

• A. Holes
• B. Free electrons
• C. Valence electrons
• D. Bound electrons

Explanation: A trivalent impurity has only three valence electrons, so it leaves one incomplete covalent bond when added to silicon or germanium.

• A. Remains the same
• B. Increases
• C. Decreases
• D. None of the above

Explanation: Doping increases the number of charge carriers, either electrons or holes, so conductivity rises.

• A. A free electron
• B. The incomplete part of an electron pair bond
• C. A free proton
• D. A free neutron

Explanation: A hole is the vacancy left by an incomplete covalent electron-pair bond.

• A. 4
• B. 5
• C. 6
• D. 3

Explanation: The term trivalent means that the impurity atom has three valence electrons.

• A. Forces between nuclei
• B. Forces between protons
• C. Electron-pair bonds
• D. None of the above

Explanation: Adjacent semiconductor atoms share valence electrons in covalent, or electron-pair, bonds.

• A. Covalent
• B. Electrovalent
• C. Co-ordinate
• D. None of the above

Explanation: Silicon and germanium form crystals through covalent bonds, in which neighboring atoms share valence electrons.

• A. 100 O cm
• B. 6000 O cm
• C. 3 x 10^5 O m
• D. 6 x 10^-8 O cm

Explanation: The commonly quoted room-temperature resistivity of pure silicon is about 6000 ohm-cm, although the exact value varies with temperature…