Free Electronics and Devices MCQs with Answers

• A. easy to make
• B. compact
• C. inexpensive
• D. all of the above reasons

Explanation: Carbon resistors are made by relatively simple processes, occupy little space, and cost less than many precision resistor types.

• A. carbon rod serves as conductor
• B. carbon can resist the attack of battery acid
• C. both (A) and (B)
• D. either (A) or (B)

Explanation: A carbon rod provides a conducting path in the cell while also resisting chemical attack from the electrolyte.

• A. Silica
• B. Germanium
• C. Selenium
• D. Gallium-arsenide

Explanation: Germanium, selenium, and gallium arsenide are semiconductor materials. Silica is silicon dioxide, an insulating compound, whereas…

• A. 1
• B. 2
• C. 4
• D. 8

Explanation: A body-centred cubic unit cell has eight corner atoms contributing one atom in total, plus one complete atom at its centre.

• A. the heat content of the crystal
• B. the temperature of the crystal
• C. the stiffness of the bonds it makes with neighbors

Explanation: The natural vibration frequency of an atom in a crystal is mainly set by the stiffness of the interatomic bonds, analogous to a…

• A. the electronic concentration and the mobility of the free electrons
• B. the number of valence electrons per atom
• C. either (A) or (B)
• D. none of the above

Explanation: Conductivity is given by σ = neμ, where n is the concentration of free electrons, e is their charge, and μ is their mobility.

• A. Aluminium is a noble metal
• B. Atmospheric oxygen can only diffuse very slowly through the oxide layer which is formed on the surface of aluminium
• C. No reaction with oxygen occurs ft Any of the above

Explanation: Aluminium rapidly forms a thin, adherent oxide film that passivates its surface and greatly slows further oxygen diffusion and reaction.

• A. the amplitude of vibration of the atoms varies with temperature
• B. the electron density varies with temperature
• C. the electron gas density varies with temperature

Explanation: As temperature rises, lattice atoms vibrate with greater amplitude and scatter conduction electrons more strongly, increasing resistivity.

• A. 2
• B. 4
• C. 7
• D. 12

Explanation: The seven crystal systems are cubic, tetragonal, orthorhombic, monoclinic, triclinic, hexagonal, and trigonal.

• A. carbon crystals
• B. solid carbon granules
• C. pulverized coal
• D. finely divided carbon black

Explanation: A carbon-composition resistor uses finely divided carbon black mixed with a binding material and formed into the resistor body.

• A. covalent
• B. metallic
• C. Vander Waals
• D. Vander Waals and covalent

Explanation: Carbon atoms within each graphite sheet are joined by strong covalent bonds, while adjacent sheets are held together by weak van der Waals…

• A. produce harmonic distortion
• B. follows Ohm's law at low temperatures only
• C. result in non-uniform heating
• D. none of the above

Explanation: A nonlinear resistor does not produce a purely sinusoidal response to a sinusoidal voltage or current, so harmonics are generated and…

• A. Organic polymers
• B. Silicon
• C. Metals

Explanation: Metals are primarily held together by metallic bonding, with delocalised electrons, whereas silicon and many organic polymers contain…

• A. adding impurities
• B. reducing temperatures
• C. application of magnetic field
• D. any of the above

Explanation: A magnetic field exceeding a superconductor's critical field disrupts its superconducting state and causes a return to normal resistance.

• A. Tin-lead
• B. Tin-silver-lead
• C. Copper-zinc
• D. None of the above

Explanation: Copper-zinc alloy, commonly called brass, has a higher melting point and greater mechanical strength than soft tin-lead solder, so it is…

• A. linear
• B. hexagonal
• C. orthorhombic
• D. cubic

Explanation: Most common metals crystallize in cubic arrangements, mainly body-centred cubic or face-centred cubic structures.

• A. increases
• B. decreases
• C. does not change

Explanation: Silicon atoms scatter the conducting electrons in iron, increasing its electrical resistivity and reducing eddy-current losses.

• A. vacuum tubes
• B. copper conductors
• C. ferrite cores
• D. transistors

Explanation: Thermionic emission is the release of electrons from a heated cathode, a process central to vacuum tubes.

• A. high resistivity
• B. high resistance to corrosion
• C. good thermal conductivity
• D. high melting point

Explanation: A good electrical contact should have low resistivity so that it produces little voltage drop and heating.

• A. Glass
• B. Quartz
• C. Corrundum
• D. Neoprene

Explanation: Quartz is a classic piezoelectric material: mechanical stress on it produces charge, and an applied voltage causes mechanical deformation.