Utilization of Electrical Energy MCQs 2026

Resistance heating element operates on the principle

1. A I²R loss producing heat in the conductor ✓
2. B Faraday law of induction only ✓
3. C photoelectric emission only ✓
4. D superconducting zero loss ✓

Design of resistance furnace element considers

1. A operating temperature, atmosphere and resistance alloy selection ✓
2. B only cable skin effect on overhead lines ✓
3. C only Buchholz gas pressure ✓
4. D only synchronous speed formula ✓

Nichrome wire is widely used in heating appliances because it has

1. A zero resistance at 1000°C ✓
2. B high resistivity and oxidation resistance at elevated temperature ✓
3. C negative temperature coefficient always ✓
4. D conductivity higher than silver ✓

Indirect resistance heating uses

1. A only arc between electrodes in the melt ✓
2. B only eddy currents inside charge without element ✓
3. C only microwave ionization of air ✓
4. D resistance elements separate from the charge, heating by radiation/conduction ✓

Direct resistance heating passes current

1. A only through insulating refractory ✓
2. B through the charge itself using electrodes ✓
3. C only through transformer core laminations ✓
4. D only through ELCB toroidal core without load ✓

Induction heating relies on

1. A eddy currents induced in the workpiece by alternating magnetic field ✓
2. B only DC resistance of cold wire ✓
3. C only visible light from filament ✓
4. D only static charge on insulator ✓

Induction heating coil is typically made of

1. A paper insulation only ✓
2. B copper tubing or litz wire with cooling ✓
3. C permanent magnet only ✓
4. D superconductor at 300 K ✓

Dielectric heating (RF/microwave) heats material by

1. A molecular friction from reorientation in high-frequency electric field ✓
2. B only conduction electrons in copper bus ✓
3. C only magnetic hysteresis in steel core at DC ✓
4. D only corona on transmission line ✓

Resistance seam welding produces

1. A only single-point nugget ✓
2. B only cutting kerf without fusion ✓
3. C only brazing with filler only ✓
4. D continuous leak-tight joint along overlapping sheets ✓

Welding cables must be

1. A flexible copper with adequate ampacity for duty current ✓
2. B thin signal wires only ✓
3. C solid overhead ACSR without insulation ✓
4. D fiber optic only ✓

Polarity in DC welding affects

1. A only power factor of fluorescent lamp ✓
2. B only traction substation location ✓
3. C only insulator creepage only ✓
4. D heat distribution between electrode and workpiece ✓

Welding hazard includes

1. A only improved power factor ✓
2. B only higher luminous flux ✓
3. C only lower cable capacitance ✓
4. D UV radiation, fumes, electric shock and fire ✓

Earthing of welding workpiece and frame prevents

1. A increased arc length always ✓
2. B mandatory ELCB bypass ✓
3. C dangerous touch voltage during insulation failure ✓
4. D higher open-circuit voltage ✓

Inverter welding power source advantage is

1. A lighter weight and better control of arc characteristics ✓
2. B only heavier copper alternator always ✓
3. C no need for any protection ✓
4. D only DC without any control ✓

Forge welding is classified as

1. A fusion arc welding only ✓
2. B solid-state joining by heating and mechanical pressure ✓
3. C only laser cutting ✓
4. D only induction furnace melting ✓

Projection welding is a variant of

1. A resistance welding using embossed projections on sheet ✓
2. B submerged arc only ✓
3. C TIG without filler ✓
4. D dielectric RF heating ✓

Preheating in welding of thick sections reduces

1. A need for any shielding gas ✓
2. B risk of cracking from rapid cooling and hydrogen embrittlement ✓
3. C electrode melting point ✓
4. D requirement for earthing ✓

DC series motor is traditionally preferred in electric traction because it provides

1. A constant speed at all torque ✓
2. B high starting torque and speed drops with load ✓
3. C zero starting torque ✓
4. D only synchronous speed operation ✓

Overhead catenary in AC electric traction supplies

1. A pantograph-collected power to locomotive ✓
2. B only signals without power ✓
3. C only diesel fuel ✓
4. D only third-rail DC only worldwide ✓

25 kV, 50 Hz single-phase traction supply is stepped down on locomotive by

1. A onboard transformer and rectifier/converter ✓
2. B only resistance heating element ✓
3. C only street lighting choke ✓
4. D only Buchholz relay ✓

Regenerative braking in electric traction returns energy

1. A only as heat in rheostat always without reuse ✓
2. B to the overhead line or grid when permitted ✓
3. C only to battery on diesel train without electric supply ✓
4. D only to insulator surface ✓

Adhesion limit in traction means

1. A maximum voltage of catenary only ✓
2. B maximum lux on platform ✓
3. C maximum welding duty cycle ✓
4. D maximum tractive effort before wheel slip ✓

Rheostatic (dynamic) braking dissipates energy in

1. A only insulator leakage ✓
2. B only transformer core alone ✓
3. C only signaling cable ✓
4. D onboard resistor grids when line cannot absorb regeneration ✓

Three-phase induction motor drive with VVVF inverter in modern EMU provides

1. A only fixed 50 Hz synchronous speed without control ✓
2. B smooth torque control and regenerative capability ✓
3. C only DC series characteristic without electronics ✓
4. D only resistance oven control ✓

Neutral section in AC traction overhead is provided to

1. A increase catenary resistance for heating ✓
2. B provide lighting to coaches only ✓
3. C separate feeding sections and avoid bridging different phases/supplies ✓
4. D measure earth fault only ✓

Traction return current typically flows through

1. A only overhead wire without return ✓
2. B rails and earthing network back to substation ✓
3. C only passenger coaches insulation ✓
4. D only platform lighting neutral ✓

Booster transformer with return conductor in AC traction reduces

1. A motor starting current in factories ✓
2. B lamp lumen depreciation ✓
3. C contact resistance in spot weld only ✓
4. D interference in nearby communication lines from traction current ✓

Specific energy consumption of traction is often expressed in

1. A lux per square meter ✓
2. B ohms per volt ✓
3. C kWh per passenger-km or per tonne-km ✓
4. D lumen per watt only ✓

DC third-rail traction at 750 V is common on

1. A only EHV transmission lines at 500 kV ✓
2. B only domestic lighting circuits ✓
3. C some metro and urban systems ✓
4. D only resistance furnace supply ✓

Pantograph uplift force must be

1. A sufficient for current collection without excessive wear or lift-off ✓
2. B zero newtons always ✓
3. C greater than locomotive weight ✓
4. D unrelated to speed ✓

Traction substation converts utility supply to

1. A only 230 V lighting without conversion ✓
2. B only welding open-circuit voltage only ✓
3. C only microwave frequency ✓
4. D traction voltage (e.g., 25 kV AC or 750 V DC) ✓

Pakistan main line electrification projects (where implemented) align with

1. A only domestic 230 V wiring without substation ✓
2. B only arc welding sets on track ✓
3. C standard gauge traction supply and NTDC/grid interconnection requirements ✓
4. D only street lighting series circuits ✓

Wheel slip detection in traction drive

1. A increases torque until burnout ✓
2. B reduces motor torque to restore adhesion ✓
3. C opens catenary circuit breaker only ✓
4. D disables all braking permanently ✓

Electric traction advantage over diesel includes

1. A higher noise always at station ✓
2. B no possibility of regeneration ✓
3. C zero tailpipe emissions at point of use and high acceleration capability ✓
4. D no need for any protection relay ✓

Line voltage drop in DC third-rail limits

1. A only lamp color temperature ✓
2. B only insulator creepage on 500 kV ✓
3. C only welding flux composition ✓
4. D spacing of feeder substations and train spacing ✓

Creeping speed in traction is achieved by

1. A disconnecting all brakes permanently ✓
2. B open-circuiting transformer ✓
3. C low-voltage tap or pulse control on motors ✓
4. D removing pantograph ✓

Coasting in traction driving saves energy by

1. A maximum braking into station always ✓
2. B short-circuiting catenary ✓
3. C cutting power and using train momentum ✓
4. D increasing heating load ✓

Arc blow in DC welding is caused by

1. A magnetic deflection of arc from surrounding fields ✓
2. B only high power factor ✓
3. C only ELCB tripping ✓
4. D only lamp depreciation ✓

Submerged arc welding features

1. A open arc in air without flux ✓
2. B only spot welds on thin foil ✓
3. C only oxy-fuel flame without electricity ✓
4. D arc hidden under granular flux blanket ✓

MIG/MAG welding feeds

1. A only static cast iron electrode without feed ✓
2. B continuous consumable wire electrode with gas shield ✓
3. C only resistance roller without arc ✓
4. D only submerged arc without wire ✓

TIG welding uses

1. A only flux-covered consumable rod without gas ✓
2. B only explosive pressure welding ✓
3. C non-consumable tungsten electrode and inert gas shielding ✓
4. D only microwave dielectric heating ✓

Duty cycle rating of welding machine indicates

1. A only power factor of supply ✓
2. B percentage of 10-minute period it can deliver rated current without overheating ✓
3. C only earth resistance in ohms ✓
4. D only luminous efficacy ✓

Welding transformer (welding set) is designed for

1. A high voltage low current like distribution ✓
2. B only open circuit without load ✓
3. C low secondary voltage and high secondary current ✓
4. D only capacitor start motor ✓

Spot welding current is high because

1. A skin effect is zero in sheets ✓
2. B voltage must be 415 kV ✓
3. C contact resistance at faying surfaces generates localized heat ✓
4. D workpieces are perfect insulators ✓

Resistance spot welding joins sheets by

1. A only arc plasma between wide gaps ✓
2. B only gas tungsten arc without current ✓
3. C only induction melting in crucible ✓
4. D passing heavy current through contact points to melt and forge metal ✓

In SMAW (stick welding), flux coating on electrode provides

1. A only DC to AC conversion ✓
2. B only traction motor field ✓
3. C only street lighting distribution ✓
4. D shielding gas, slag protection and arc stabilization ✓

Open-circuit voltage of arc welding machine is kept

1. A zero always during welding ✓
2. B equal to mains without any limit ✓
3. C high enough to strike arc but limited for safety ✓
4. D negative voltage only ✓

Arc welding heat is produced primarily by

1. A electric arc between electrode and workpiece ✓
2. B only resistance of insulator ✓
3. C only transformer no-load loss ✓
4. D only magnetic hysteresis in core ✓

Safety in electric heating installations requires

1. A bypassing all thermal cutouts ✓
2. B removing earth connection ✓
3. C using undersized cable intentionally ✓
4. D proper earthing, temperature sensors and overcurrent protection ✓

Skin effect in induction heating workpiece at high frequency causes

1. A uniform heating through entire thickness always ✓
2. B no eddy currents ✓
3. C heating concentrated nearer the surface ✓
4. D cooling of surface only ✓

Batch annealing with electric resistance furnaces offers

1. A only arc blow in welding ✓
2. B only regenerative traction braking ✓
3. C only ELCB nuisance tripping ✓
4. D clean atmosphere control and uniform temperature profiling ✓

Dielectric loss factor tan δ in heating applications indicates

1. A only DC resistance of copper ✓
2. B only synchronous reactance ✓
3. C efficiency of converting RF energy to heat in the material ✓
4. D only earth electrode resistance ✓

Specific heat of material affects electric heating time because

1. A energy required equals mass × specific heat × temperature rise ✓
2. B only cable length determines heat ✓
3. C only power factor angle determines heat ✓
4. D only lux level determines heat ✓

Electric oven thermostat maintains temperature by

1. A increasing voltage without limit ✓
2. B cycling power on/off or proportional control around set point ✓
3. C shorting heating element always ✓
4. D disconnecting neutral only ✓

Coreless induction furnace uses

1. A only DC battery supply without inverter ✓
2. B high-frequency field to melt metal in crucible without iron core ✓
3. C only permanent magnet static field ✓
4. D only resistance wire buried in concrete ✓

Infrared quartz heater element is usually

1. A tungsten filament in quartz tube radiating IR ✓
2. B liquid sodium only ✓
3. C SF6 gas discharge only ✓
4. D transformer oil only ✓

Power control in resistance heating is often by

1. A only open-circuit transformer test ✓
2. B only permanent short circuit ✓
3. C thyristor phase-angle firing or contactor switching ✓
4. D only increasing fuse rating without control ✓

Three-phase star-connected heating load on 415 V line has phase voltage

1. A 415 V on each phase to neutral always incorrectly as line ✓
2. B zero V always ✓
3. C 830 V phase voltage ✓
4. D 240 V (approximately for 415 V line-to-line) ✓

Maximum temperature of open resistance element in air is limited by

1. A only supply frequency 50 Hz ✓
2. B oxidation and creep of alloy at high temperature ✓
3. C only power factor of motor ✓
4. D only street lighting lux ✓

Infrared heating panels primarily deliver heat by

1. A thermal radiation in the IR spectrum ✓
2. B only forced convection of cold air ✓
3. C only magnetic flux linkage ✓
4. D only electrolysis of water ✓