Electrical Materials MCQs 2026

Coercivity represents

1. A maximum permeability value ✓
2. B core weight only ✓
3. C magnetizing force needed to reduce flux density to zero ✓
4. D turns ratio of transformer ✓

Among common metals used as conductors, silver has

1. A lower conductivity than aluminum ✓
2. B the highest electrical conductivity ✓
3. C conductivity equal to iron ✓
4. D conductivity half that of copper ✓

Contact resistance at a bolted joint depends strongly on

1. A contact pressure and surface cleanliness ✓
2. B only conductor length ✓
3. C only ambient humidity without pressure ✓
4. D color of insulation ✓

Annealing copper wire after drawing

1. A restores ductility and lowers resistivity slightly ✓
2. B increases hardness permanently ✓
3. C makes wire magnetic ✓
4. D eliminates need for insulation ✓

Bus bars for high continuous current often use

1. A only iron wire ✓
2. B only superconductor at room temperature ✓
3. C only paper insulation ✓
4. D copper or aluminum with adequate cross-section and ventilation ✓

AAC in overhead conductors stands for

1. A All Aluminum Conductor ✓
2. B Aluminum Alloy Cable ✓
3. C Annealed Aluminum Core ✓
4. D Active AC Conductor ✓

ACSR conductor improves strength by

1. A pure copper core only ✓
2. B glass fiber only ✓
3. C steel core supporting aluminum strands ✓
4. D eliminating aluminum strands ✓

Porcelain insulators are widely used outdoors because they have

1. A very low mechanical strength only ✓
2. B high dielectric strength and weather resistance ✓
3. C conductivity equal to copper ✓
4. D zero creepage requirement ✓

Glass insulators compared to porcelain typically offer

1. A easier visual inspection of defects ✓
2. B lower dielectric strength always ✓
3. C higher weight per unit always ✓
4. D no need for creepage distance ✓

Composite polymer insulators advantage over porcelain includes

1. A mandatory higher leakage always ✓
2. B no creepage needed ever ✓
3. C lighter weight and better vandal/impact resistance ✓
4. D cannot be used on transmission lines ✓

Dielectric breakdown of a solid insulator decreases when

1. A temperature falls to absolute zero only ✓
2. B temperature rises or moisture penetrates the material ✓
3. C thickness increases without limit ✓
4. D voltage is removed ✓

Dielectric strength of an insulating material is expressed as

1. A ohms per meter only ✓
2. B volts per unit thickness (kV/mm) ✓
3. C henries per turn ✓
4. D watts per lumen ✓

Creepage distance on an insulator is the

1. A straight-line distance through the core only ✓
2. B weight of the insulator ✓
3. C current rating in amperes ✓
4. D surface path length along the insulator between live and earth ✓

Mica is valued as an insulator because it withstands

1. A only cryogenic temperatures ✓
2. B only DC without any AC ✓
3. C high temperature and has excellent dielectric properties ✓
4. D only magnetic flux without insulation ✓

Varnished cambric tape insulation is classified as

1. A solid organic insulation for coils and cables ✓
2. B superconducting material ✓
3. C magnetic core lamination ✓
4. D liquid dielectric only ✓

Bakelite (phenol formaldehyde) is an example of

1. A superconductor ✓
2. B thermosetting plastic insulator ✓
3. C ferromagnetic core steel ✓
4. D liquid coolant ✓

Sulfur hexafluoride (SF6) gas in switchgear serves as

1. A only lubricant for contacts ✓
2. B only visible indicator gas ✓
3. C only heating element ✓
4. D high dielectric strength insulation and arc quenching medium ✓

Surface tracking on polluted insulators is caused by

1. A only DC resistance of conductor ✓
2. B only skin effect in conductor ✓
3. C dry-band arcing and carbonized paths on the surface ✓
4. D only transformer magnetizing current ✓

For cable insulation, a lower dielectric constant generally means

1. A higher capacitance always ✓
2. B lower capacitance and charging current per unit length ✓
3. C higher conductor resistance ✓
4. D zero breakdown voltage ✓

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

1. A high permeability and low hysteresis loss ✓
2. B very high coercivity ✓
3. C permeability equal to air only ✓
4. D no saturation flux density ✓

Silicon added to electrical steel reduces

1. A hysteresis loss and eddy current loss ✓
2. B permeability to zero ✓
3. C saturation flux density to zero ✓
4. D need for lamination ✓

Hysteresis loss in a magnetic core per cycle is proportional to

1. A only supply frequency squared only without flux ✓
2. B only conductor length ✓
3. C the area of the B-H hysteresis loop ✓
4. D only cable capacitance ✓

Lamination of transformer core reduces eddy current loss by

1. A increasing core thickness solidly ✓
2. B eliminating flux entirely ✓
3. C increasing resistance to circulating currents in the core ✓
4. D using only air core ✓

Hard magnetic materials (permanent magnets) are characterized by

1. A very low coercivity ✓
2. B high retentivity and high coercivity ✓
3. C permeability equal to vacuum only ✓
4. D zero remanence ✓

Ferrite cores are preferred at high frequency because they have

1. A higher conductivity than copper ✓
2. B high resistivity hence low eddy current loss ✓
3. C no need for any winding ✓
4. D infinite permeability at all frequencies ✓

Curie temperature of a ferromagnetic material is the temperature at which

1. A ferromagnetic property is lost and material becomes paramagnetic ✓
2. B permeability becomes infinite ✓
3. C resistivity becomes zero ✓
4. D insulation breaks down ✓

Retentivity (remanence) of a magnetic material measures

1. A flux density retained after removing magnetizing force ✓
2. B initial permeability only ✓
3. C coil resistance only ✓
4. D dielectric constant only ✓

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

1. A exactly 1 always ✓
2. B less than 1 always ✓
3. C equal to copper conductivity ✓
4. D several hundred to a few thousand ✓

Steinmetz equation for hysteresis loss is of the form

1. A Ph = k f B^n ✓
2. B Ph = I²R only ✓
3. C Ph = V²/R only ✓
4. D Ph = f² only without flux ✓

Grain-oriented silicon steel in transformers aligns grains to

1. A reduce hysteresis and eddy losses along flux direction ✓
2. B increase eddy paths deliberately ✓
3. C eliminate need for windings ✓
4. D increase air gap only ✓

Mumetal and similar nickel-iron alloys are used for

1. A high voltage outdoor insulators ✓
2. B magnetic shielding of sensitive instruments ✓
3. C resistance heating elements ✓
4. D overhead line conductors only ✓

A superconductor below its critical temperature exhibits

1. A infinite resistance always ✓
2. B same resistivity as copper ✓
3. C zero DC electrical resistance ✓
4. D only magnetic insulation without conduction ✓

The Meissner effect in superconductors refers to

1. A increase of resistance below Tc ✓
2. B emission of light under voltage ✓
3. C expulsion of magnetic flux from the interior ✓
4. D thermal runaway in the core ✓

Critical current density Jc in a superconductor is the

1. A room-temperature ampacity of copper ✓
2. B maximum current per unit area before superconductivity is destroyed ✓
3. C charging current of a cable only ✓
4. D magnetizing current of transformer ✓

Type I superconductors exhibit

1. A flux pinning for high-field magnets at 77 K ✓
2. B complete Meissner effect below critical field and are mostly pure metals ✓
3. C Tc above 200 K routinely ✓
4. D use in household wiring at room temperature ✓

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

1. A no current carrying ability ✓
2. B only insulation duty ✓
3. C mixed state with flux pinning above lower critical field ✓
4. D operation without any cooling ✓

YBCO high-temperature superconductor has critical temperature around

1. A 300 K ✓
2. B 4 K only ✓
3. C 273 K exactly ✓
4. D 90 K ✓

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

1. A 300 K ambient ✓
2. B 77 K only without helium ever ✓
3. C 200 K with water ✓
4. D 4 K with liquid helium ✓

BCS theory explains superconductivity through

1. A Cooper pairs of electrons coupled by lattice vibrations ✓
2. B only classical Ohm law ✓
3. C only hysteresis in iron cores ✓
4. D only eddy currents in laminations ✓

AC loss in superconducting cables arises from

1. A only DC resistance below Tc ✓
2. B only corona on overhead lines ✓
3. C only contact resistance at joints ✓
4. D hysteresis and coupling losses when flux penetrates the conductor ✓

Flux pinning in type II superconductors enables

1. A zero current always in any field ✓
2. B complete loss of superconductivity at zero field ✓
3. C high critical current in applied magnetic fields ✓
4. D use as dielectric insulator only ✓

Josephson junction devices exploit

1. A only thermal emission of electrons ✓
2. B only arc discharge in SF6 ✓
3. C only transformer mutual flux ✓
4. D tunneling of Cooper pairs between superconductors ✓

Conventional low-Tc superconductors require cryogenic cooling because

1. A they operate at 500°C ✓
2. B they are insulators above Tc only without cooling need ✓
3. C copper becomes superconducting at room temperature ✓
4. D critical temperature is only a few kelvin above absolute zero ✓

Resistivity of annealed copper at 20°C is approximately

1. A 1.7 × 10⁻⁸ ohm·m ✓
2. B 17 × 10⁻⁸ ohm·m ✓
3. C 0.17 × 10⁻⁸ ohm·m ✓
4. D 1.7 × 10⁻⁶ ohm·m ✓

Aluminum conductor compared to equal-size copper has

1. A lower resistance than copper ✓
2. B same conductivity as silver ✓
3. C zero skin effect ✓
4. D higher resistance and lower conductivity ✓

Stranded conductors are preferred over solid conductors in flexible cables because

1. A stranding increases DC resistance always ✓
2. B solid wire has higher ampacity always ✓
3. C stranding eliminates skin effect ✓
4. D stranding reduces breakage from bending ✓

Skin effect in AC conductors causes

1. A uniform current density at all frequencies ✓
2. B current only in the core ✓
3. C current concentration near the outer surface at higher frequency ✓
4. D zero resistance at surface ✓

Proximity effect in parallel conductors results from

1. A only DC resistance change ✓
2. B distortion of magnetic field between adjacent current-carrying conductors ✓
3. C only insulation breakdown ✓
4. D only corona on insulators ✓

Hard-drawn copper wire compared to annealed copper has

1. A lower strength and lower resistivity ✓
2. B higher tensile strength but slightly higher resistivity ✓
3. C identical mechanical and electrical properties ✓
4. D zero creep at all temperatures ✓

Tinned copper conductors are used primarily to

1. A increase conductivity above silver ✓
2. B eliminate skin effect ✓
3. C replace insulation entirely ✓
4. D prevent surface oxidation and ease soldering ✓