Free Electronics and Devices MCQs with Answers

• A. resonant waves
• B. musical waves
• C. microwaves
• D. ultrasonic waves

Explanation: Piezoelectric crystals convert electrical energy into mechanical vibrations and are commonly driven at high frequency to generate…

• A. Cast-iron
• B. Graphite
• C. Rubber
• D. Glass

Explanation: Rubber is viscoelastic, so it shows both elastic recovery and time-dependent viscous deformation.

• A. copper and aluminium
• B. tin and lead
• C. nickel, copper and zinc
• D. silver, copper and lead

Explanation: Traditional solder is a low-melting alloy of tin and lead, allowing components and wires to be joined without melting the base metals.

• A. GLS lamps
• B. electric arc furnace
• C. dry cells
• D. cinema projectors

Explanation: Carbon electrodes are used in arc furnaces, dry-cell batteries, and carbon-arc cinema projectors.

• A. Silver nitrate
• B. Ferric oxide
• C. Small particles of iron
• D. Silicon-iron

Explanation: Magnetic recording tape is coated with fine ferric oxide particles, which retain magnetisation corresponding to the recorded signal.

• A. Fe203
• B. Si02
• C. AI2O3
• D. B2O3

Explanation: Silica, SiO₂, forms the principal glass-forming material and gives ordinary glass its rigid network.

• A. Induction hardened copper
• B. Hard drawn copper
• C. Pure annealed copper
• D. Copper containing traces of silicon

Explanation: Pure annealed copper has the highest conductivity because it contains very few resistivity-increasing impurities and has a soft…

• A. Carbon
• B. Steel
• C. Silver
• D. Aluminium

Explanation: Among these choices, carbon has the greatest electrical resistivity, whereas silver is the best conductor and aluminium is also highly…

• A. silver and tin
• B. copper and tungsten
• C. tungsten and silver
• D. copper and nickel

Explanation: Constantan is a copper-nickel alloy, commonly containing roughly 55% copper and 45% nickel.

• A. critical magnetic field
• B. transition temperature
• C. critical current density
• D. none of the above

Explanation: Critical current density depends strongly on the material's structure, including defects, grain boundaries, and geometry, so it is…

• A. 18.0°K
• B. 9.22°K
• C. 4.12°K
• D. 1.14'K

Explanation: Mercury becomes superconducting at approximately 4.12 K, its transition temperature.

• A. zero
• B. negative real value
• C. positive real value
• D. complex value

Explanation: The critical magnetic field falls to zero at the transition temperature because the material loses superconductivity at that point.

• A. decreases
• B. increases
• C. remains constant
• D. becomes temperature independent

Explanation: Impurity atoms disturb the regular lattice and scatter conduction electrons, increasing residual resistivity.

• A. electric field
• B. magnetic field
• C. electromagnetic field
• D. none of the above

Explanation: An electric field exerts force on free electrons and produces their directed drift, which is the basis of conduction current.

• A. a liquid
• B. a metal
• C. a metal liquid
• D. a gas

Explanation: Mercury is a metal that is liquid at ordinary room temperature, so it is commonly described as a liquid metal.

• A. infrared frequencies
• B. d.c. and low frequency
• C. a.c. and high frequency
• D. frequencies having no effect
• E. none of the above

Explanation: Superconductivity is most practically observed with direct current and at low frequencies, where AC losses remain small.

• A. precision instruments
• B. heating elements
• C. motor starters
• D. incandescent lamps
• E. all of the above

Explanation: High-resistivity materials limit current and dissipate power, so they are used in precision resistors, heating elements, motor-starter…

• A. magnetic field strength
• B. temperature
• C. either (A) or (B)
• D. both (A) and (B)

Explanation: The critical current density of a superconductor varies with both temperature and applied magnetic-field strength, generally decreasing as…

• A. decreasing its temperature
• B. increasing its temperature
• C. decreasing its vibration
• D. increasing its vibration

Explanation: In metallic conductors, lowering temperature reduces lattice vibrations and electron scattering, thereby increasing conductivity.

• A. generating very strong magnetic field
• B. manufacture of bubble memories
• C. generating electrostatic field
• D. generating regions free from magnetic field

Explanation: A superconductor can carry very large current with negligible resistance, producing extremely strong magnetic fields in devices such as…