Electrical Materials MCQs 2026

Conventional low-Tc superconductors require cryogenic cooling because

1. Athey operate at 500°C✓
2. Bthey are insulators above Tc only without cooling need✓
3. Ccopper becomes superconducting at room temperature✓
4. Dcritical temperature is only a few kelvin above absolute zero✓

Josephson junction devices exploit

1. Aonly thermal emission of electrons✓
2. Bonly arc discharge in SF6✓
3. Conly transformer mutual flux✓
4. Dtunneling of Cooper pairs between superconductors✓

Flux pinning in type II superconductors enables

1. Azero current always in any field✓
2. Bcomplete loss of superconductivity at zero field✓
3. Chigh critical current in applied magnetic fields✓
4. Duse as dielectric insulator only✓

AC loss in superconducting cables arises from

1. Aonly DC resistance below Tc✓
2. Bonly corona on overhead lines✓
3. Conly contact resistance at joints✓
4. Dhysteresis and coupling losses when flux penetrates the conductor✓

BCS theory explains superconductivity through

1. ACooper pairs of electrons coupled by lattice vibrations✓
2. Bonly classical Ohm law✓
3. Conly hysteresis in iron cores✓
4. Donly eddy currents in laminations✓

Nb-Ti alloy superconducting wire in MRI magnets is typically cooled to about

1. A300 K ambient✓
2. B77 K only without helium ever✓
3. C200 K with water✓
4. D4 K with liquid helium✓

YBCO high-temperature superconductor has critical temperature around

1. A300 K✓
2. B4 K only✓
3. C273 K exactly✓
4. D90 K✓

Type II superconductors are used in high-field magnets because they allow

1. Ano current carrying ability✓
2. Bonly insulation duty✓
3. Cmixed state with flux pinning above lower critical field✓
4. Doperation without any cooling✓

Type I superconductors exhibit

1. Aflux pinning for high-field magnets at 77 K✓
2. Bcomplete Meissner effect below critical field and are mostly pure metals✓
3. CTc above 200 K routinely✓
4. Duse in household wiring at room temperature✓

Critical current density Jc in a superconductor is the

1. Aroom-temperature ampacity of copper✓
2. Bmaximum current per unit area before superconductivity is destroyed✓
3. Ccharging current of a cable only✓
4. Dmagnetizing current of transformer✓

The Meissner effect in superconductors refers to

1. Aincrease of resistance below Tc✓
2. Bemission of light under voltage✓
3. Cexpulsion of magnetic flux from the interior✓
4. Dthermal runaway in the core✓

A superconductor below its critical temperature exhibits

1. Ainfinite resistance always✓
2. Bsame resistivity as copper✓
3. Czero DC electrical resistance✓
4. Donly magnetic insulation without conduction✓

Mumetal and similar nickel-iron alloys are used for

1. Ahigh voltage outdoor insulators✓
2. Bmagnetic shielding of sensitive instruments✓
3. Cresistance heating elements✓
4. Doverhead line conductors only✓

Grain-oriented silicon steel in transformers aligns grains to

1. Areduce hysteresis and eddy losses along flux direction✓
2. Bincrease eddy paths deliberately✓
3. Celiminate need for windings✓
4. Dincrease air gap only✓

Steinmetz equation for hysteresis loss is of the form

1. APh = k f B^n✓
2. BPh = I²R only✓
3. CPh = V²/R only✓
4. DPh = f² only without flux✓

Relative permeability μr of soft iron can be of the order of

1. Aexactly 1 always✓
2. Bless than 1 always✓
3. Cequal to copper conductivity✓
4. Dseveral hundred to a few thousand✓

Coercivity represents

1. Amaximum permeability value✓
2. Bcore weight only✓
3. Cmagnetizing force needed to reduce flux density to zero✓
4. Dturns ratio of transformer✓

Retentivity (remanence) of a magnetic material measures

1. Aflux density retained after removing magnetizing force✓
2. Binitial permeability only✓
3. Ccoil resistance only✓
4. Ddielectric constant only✓

Curie temperature of a ferromagnetic material is the temperature at which

1. Aferromagnetic property is lost and material becomes paramagnetic✓
2. Bpermeability becomes infinite✓
3. Cresistivity becomes zero✓
4. Dinsulation breaks down✓

Ferrite cores are preferred at high frequency because they have

1. Ahigher conductivity than copper✓
2. Bhigh resistivity hence low eddy current loss✓
3. Cno need for any winding✓
4. Dinfinite permeability at all frequencies✓

Hard magnetic materials (permanent magnets) are characterized by

1. Avery low coercivity✓
2. Bhigh retentivity and high coercivity✓
3. Cpermeability equal to vacuum only✓
4. Dzero remanence✓

Lamination of transformer core reduces eddy current loss by

1. Aincreasing core thickness solidly✓
2. Beliminating flux entirely✓
3. Cincreasing resistance to circulating currents in the core✓
4. Dusing only air core✓

Hysteresis loss in a magnetic core per cycle is proportional to

1. Aonly supply frequency squared only without flux✓
2. Bonly conductor length✓
3. Cthe area of the B-H hysteresis loop✓
4. Donly cable capacitance✓

Silicon added to electrical steel reduces

1. Ahysteresis loss and eddy current loss✓
2. Bpermeability to zero✓
3. Csaturation flux density to zero✓
4. Dneed for lamination✓

Soft magnetic materials such as silicon steel are used in transformer cores because they have

1. Ahigh permeability and low hysteresis loss✓
2. Bvery high coercivity✓
3. Cpermeability equal to air only✓
4. Dno saturation flux density✓

For cable insulation, a lower dielectric constant generally means

1. Ahigher capacitance always✓
2. Blower capacitance and charging current per unit length✓
3. Chigher conductor resistance✓
4. Dzero breakdown voltage✓

Surface tracking on polluted insulators is caused by

1. Aonly DC resistance of conductor✓
2. Bonly skin effect in conductor✓
3. Cdry-band arcing and carbonized paths on the surface✓
4. Donly transformer magnetizing current✓

Sulfur hexafluoride (SF6) gas in switchgear serves as

1. Aonly lubricant for contacts✓
2. Bonly visible indicator gas✓
3. Conly heating element✓
4. Dhigh dielectric strength insulation and arc quenching medium✓

Bakelite (phenol formaldehyde) is an example of

1. Asuperconductor✓
2. Bthermosetting plastic insulator✓
3. Cferromagnetic core steel✓
4. Dliquid coolant✓

Varnished cambric tape insulation is classified as

1. Asolid organic insulation for coils and cables✓
2. Bsuperconducting material✓
3. Cmagnetic core lamination✓
4. Dliquid dielectric only✓

Mica is valued as an insulator because it withstands

1. Aonly cryogenic temperatures✓
2. Bonly DC without any AC✓
3. Chigh temperature and has excellent dielectric properties✓
4. Donly magnetic flux without insulation✓

Creepage distance on an insulator is the

1. Astraight-line distance through the core only✓
2. Bweight of the insulator✓
3. Ccurrent rating in amperes✓
4. Dsurface path length along the insulator between live and earth✓

Dielectric strength of an insulating material is expressed as

1. Aohms per meter only✓
2. Bvolts per unit thickness (kV/mm)✓
3. Chenries per turn✓
4. Dwatts per lumen✓

Dielectric breakdown of a solid insulator decreases when

1. Atemperature falls to absolute zero only✓
2. Btemperature rises or moisture penetrates the material✓
3. Cthickness increases without limit✓
4. Dvoltage is removed✓

Composite polymer insulators advantage over porcelain includes

1. Amandatory higher leakage always✓
2. Bno creepage needed ever✓
3. Clighter weight and better vandal/impact resistance✓
4. Dcannot be used on transmission lines✓

Glass insulators compared to porcelain typically offer

1. Aeasier visual inspection of defects✓
2. Blower dielectric strength always✓
3. Chigher weight per unit always✓
4. Dno need for creepage distance✓

Porcelain insulators are widely used outdoors because they have

1. Avery low mechanical strength only✓
2. Bhigh dielectric strength and weather resistance✓
3. Cconductivity equal to copper✓
4. Dzero creepage requirement✓

ACSR conductor improves strength by

1. Apure copper core only✓
2. Bglass fiber only✓
3. Csteel core supporting aluminum strands✓
4. Deliminating aluminum strands✓

AAC in overhead conductors stands for

1. AAll Aluminum Conductor✓
2. BAluminum Alloy Cable✓
3. CAnnealed Aluminum Core✓
4. DActive AC Conductor✓

Bus bars for high continuous current often use

1. Aonly iron wire✓
2. Bonly superconductor at room temperature✓
3. Conly paper insulation✓
4. Dcopper or aluminum with adequate cross-section and ventilation✓

Annealing copper wire after drawing

1. Arestores ductility and lowers resistivity slightly✓
2. Bincreases hardness permanently✓
3. Cmakes wire magnetic✓
4. Deliminates need for insulation✓

Contact resistance at a bolted joint depends strongly on

1. Acontact pressure and surface cleanliness✓
2. Bonly conductor length✓
3. Conly ambient humidity without pressure✓
4. Dcolor of insulation✓

Among common metals used as conductors, silver has

1. Alower conductivity than aluminum✓
2. Bthe highest electrical conductivity✓
3. Cconductivity equal to iron✓
4. Dconductivity half that of copper✓

Tinned copper conductors are used primarily to

1. Aincrease conductivity above silver✓
2. Beliminate skin effect✓
3. Creplace insulation entirely✓
4. Dprevent surface oxidation and ease soldering✓

Hard-drawn copper wire compared to annealed copper has

1. Alower strength and lower resistivity✓
2. Bhigher tensile strength but slightly higher resistivity✓
3. Cidentical mechanical and electrical properties✓
4. Dzero creep at all temperatures✓

Proximity effect in parallel conductors results from

1. Aonly DC resistance change✓
2. Bdistortion of magnetic field between adjacent current-carrying conductors✓
3. Conly insulation breakdown✓
4. Donly corona on insulators✓

Skin effect in AC conductors causes

1. Auniform current density at all frequencies✓
2. Bcurrent only in the core✓
3. Ccurrent concentration near the outer surface at higher frequency✓
4. Dzero resistance at surface✓

Stranded conductors are preferred over solid conductors in flexible cables because

1. Astranding increases DC resistance always✓
2. Bsolid wire has higher ampacity always✓
3. Cstranding eliminates skin effect✓
4. Dstranding reduces breakage from bending✓

Aluminum conductor compared to equal-size copper has

1. Alower resistance than copper✓
2. Bsame conductivity as silver✓
3. Czero skin effect✓
4. Dhigher resistance and lower conductivity✓

Resistivity of annealed copper at 20°C is approximately

1. A1.7 × 10⁻⁸ ohm·m✓
2. B17 × 10⁻⁸ ohm·m✓
3. C0.17 × 10⁻⁸ ohm·m✓
4. D1.7 × 10⁻⁶ ohm·m✓