Basic Electrical Engineering PYQs: 50 Previous Year Questions with Answers

Basic Electrical Engineering past year question papers will assist you in practicing concepts via questions that have been asked in recruitment examinations. Here you can find 50 past year question papers with choices, right answers, explanations, and exam details.

These questions have been picked up from State PSC recruitment examinations held between the years 2022 to 2025. These include questions from recruitment examinations of the posts of Electrical Engineer, Electrician, Lineman, Overseer, Draftsman, Junior Instructor, and Electrician cum Mechanic.

However, these examinations are of Kerala PSC.

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Basic Electrical Engineering PYQs: Quick Overview

Basic Electrical Engineering PYQs are questions previously asked in examinations on electrical circuits, magnetism, machines, transformers, measurements, batteries and electronics. This collection contains 50 questions with verified answers. Each question includes its examination and original paper number for reference.

How to Practise These Electrical Engineering PYQs

Attempt each question before reading its answer. For numerical problems, write the formula and convert quantities to consistent units first. After checking the explanation, revise the concept behind any incorrect answer.

Q1. Above its resonant frequency, how does a series RLC circuit behave?

A. Inductively
B. Capacitively
C. Resistively
D. Either inductively or capacitively

Correct Answer: A. Inductively

Explanation: Above resonance, inductive reactance exceeds capacitive reactance. The net reactance is therefore inductive.

Q2. For maximum AC power transfer, what load impedance should match a source impedance Z?

A. The real component of Z
B. Z/2
C. Z itself
D. The complex conjugate Z*

Correct Answer: D. The complex conjugate Z*

Explanation: Conjugate matching cancels the source reactance and matches the load resistance to the source resistance.

Q3. Three 9 Ω resistors form a delta. What is each resistance in the equivalent star?

A. 18 Ω
B. 6 Ω
C. 3 Ω
D. 4.5 Ω

Correct Answer: C. 3 Ω

Explanation: For three equal delta resistances, each equivalent star resistance is one-third of the delta resistance:\[ R_Y=\frac{R_\Delta}{3}=\frac{9}{3}=3\ \Omega \]

Q4. According to Lenz’s law, what does the induced EMF oppose?

A. Magnetic flux
B. A change in magnetic flux
C. Both flux and its change
D. Neither of these

Correct Answer: B. A change in magnetic flux

Explanation: The induced effect opposes the change in magnetic flux that produces it. It does not necessarily oppose the existing flux itself.

Q5. A 5 cm coil has 10 turns carrying 1.5 A. Find its magnetising force.

A. 150 AT/m
B. 600 AT/m
C. 450 AT/m
D. 300 AT/m

Correct Answer: D. 300 AT/m

Explanation: Using \(H=NI/l\):\[ H=\frac{10\times1.5}{0.05}=300\ \text{AT/m} \]

The coil length must be converted from centimetres to metres.

Q6. How many segments make up the usual LED digit display of a digital multimeter?

A. 6
B. 8
C. 7
D. 9

Correct Answer: C. 7

Explanation: Seven controlled segments form the numerical digits. A decimal point, where present, is separate from these seven segments.

Q7. What is the purpose of an explosion vent on a power transformer?

A. Releasing air
B. Releasing moisture
C. Relieving pressure
D. Relieving overload

Correct Answer: C. Relieving pressure

Explanation: The vent releases excessive internal pressure that may develop during a serious internal fault.

Q8. Which diode has a negative-resistance region in its characteristic?

A. A rectifier diode
B. A tunnel diode
C. A Zener diode
D. A PIN diode

Correct Answer: B. A tunnel diode

Explanation: In part of a tunnel diode’s characteristic, current decreases as voltage increases. This is called negative differential resistance.

Q9. Which steam-power-plant device heats boiler feedwater using heat recovered from flue gases?

A. Air preheater
B. Economiser
C. Superheater
D. Feedwater heater

Correct Answer: B. Economiser

Explanation: An economiser transfers waste heat from flue gases to feedwater before it enters the boiler.

Q10. What does ACSR stand for?

A. All Conductors Selected Reinforced
B. Aluminium Conductor Steel Reinforced
C. All Conductors Steel Reinforced
D. Aluminium Conductor Selected Reinforced

Correct Answer: B. Aluminium Conductor Steel Reinforced

Explanation: Aluminium carries the current, while the steel core provides mechanical strength.

Batteries, Solar Cells and DC Motor Braking

Q11. What is the nominal voltage of one standard lead-acid cell?

A. 1.2 V
B. 1.5 V
C. 2 V
D. 6 V

Correct Answer: C. 2 V

Explanation: One lead-acid cell is nominally 2 V. Three cells connected in series form a nominal 6 V battery.

Q12. Which listed material is used to manufacture solar cells?

A. Carbon
B. Magnesium
C. Sodium
D. Silicon

Correct Answer: D. Silicon

Explanation: Silicon is the semiconductor used in conventional crystalline solar cells.

Q13. Into which form of energy does a solar cell convert light?

A. Heat
B. Electrical energy
C. Chemical energy
D. Sound

Correct Answer: B. Electrical energy

Explanation: Photovoltaic action converts absorbed light directly into electrical energy.

Q14. Which material forms the filament of an incandescent lamp?

A. Tungsten
B. Copper
C. Thorium
D. Titanium

Correct Answer: A. Tungsten

Explanation: Tungsten withstands the high temperature needed for the filament to emit visible light.

Q15. Which operating method reverses the supply voltage of a separately excited DC motor?

A. Forward motoring
B. Forward regenerative braking
C. Forward dynamic braking
D. Forward plugging

Correct Answer: D. Forward plugging

Explanation: Reversing the armature supply while maintaining field polarity produces braking torque. The original paper’s typo “revered” has been corrected to “reversed.”

Q16. What principle enables a two-winding transformer to work?

A. Self-induction
B. Mutual induction
C. Electromagnetic drag
D. Conduction

Correct Answer: B. Mutual induction

Explanation: Changing primary current creates magnetic flux linking the secondary winding and induces voltage in it.

Q17. Which quantity remains unchanged during transformer action?

A. Current
B. Voltage
C. Frequency
D. Temperature

Correct Answer: C. Frequency

Explanation: A transformer changes voltage and current levels, but its output frequency equals the input frequency.

Q18. Which unit expresses “lamp efficiency” in the question’s terminology?

A. Lumen-second
B. Lumen
C. Lumen per watt
D. Lux

Correct Answer: C. Lumen per watt

Explanation: The precise term is luminous efficacy: luminous flux divided by electrical input power, measured in lm/W.

Q19. If the distance from a light source doubles, what happens to illumination?

A. It doubles
B. It quadruples
C. It halves
D. It becomes one-quarter

Correct Answer: D. It becomes one-quarter

Explanation: For a point source with unchanged incidence angle, illumination follows the inverse-square law:\[ E\propto\frac{1}{r^2} \]

Doubling the distance reduces illumination to one-quarter.

Q20. What is the ripple factor of a single-phase full-wave bridge rectifier?

A. 0.482
B. 0.812
C. 1.11
D. 1.21

Correct Answer: A. 0.482

Explanation: This is the conventional approximate value for an ideal, unfiltered full-wave output with a resistive load. Adding a filter changes the ripple factor.

Q21. Varying field flux for speed control gives which type of drive?

A. Variable-torque drive
B. Variable-power drive
C. Constant-torque drive
D. Constant-power drive

Correct Answer: D. Constant-power drive

Explanation: In the usual DC field-weakening region, speed rises while available torque falls, giving approximately constant-power operation.

Q22. When does an induction motor operate with a lagging power factor?

A. Only while starting
B. Only while running
C. During starting and running
D. When stationary

Correct Answer: C. During starting and running

Explanation: An ordinary induction motor draws inductive magnetising current during both starting and running.

Q23. What input and output impedances should an ideal voltage amplifier have?

A. Low input; high output
B. High input; high output
C. Low input; low output
D. High input; low output

Correct Answer: D. High input; low output

Explanation: Ideally, infinite input impedance avoids source loading, while zero output impedance maintains the output voltage under load.

Q24. What role does a DIAC perform in a power-control circuit?

A. Rectification
B. Triggering
C. Oscillation
D. Amplification

Correct Answer: B. Triggering

Explanation: A DIAC commonly supplies bidirectional triggering pulses to a TRIAC in an AC power-control circuit.

Q25. Which unit supplies power internally in a computer?

A. CVT
B. UPS
C. SMPS
D. Stabiliser

Correct Answer: C. SMPS

Explanation: A switched-mode power supply provides regulated DC outputs. The original uses “CPU” loosely for the computer system unit; this wording is clarified here.

Q26. What type of resistor is a varistor?

A. Linear resistor
B. Carbon resistor
C. Resistor having zero temperature coefficient
D. Nonlinear resistor

Correct Answer: D. Nonlinear resistor

Explanation: A varistor’s resistance changes with applied voltage. This property enables it to suppress voltage surges.

Q27. What is a circuit called when its properties are the same in either direction?

A. Unilateral circuit
B. Irreversible circuit
C. Bilateral circuit
D. Short circuit

Correct Answer: C. Bilateral circuit

Explanation: A bilateral circuit has the same characteristics when current direction is reversed.

Q28. Which substance serves as the depolariser in a Leclanché cell?

A. NH₄Cl
B. Mn₂O₃
C. MnO₂
D. KOH

Correct Answer: C. MnO₂

Explanation: Manganese dioxide is the depolarising material. Ammonium chloride serves as the electrolyte.

Q29. What is the relative permeability of a diamagnetic material?

A. Below 1
B. Above 1
C. Above 100
D. Equal to that of a ferromagnetic material

Correct Answer: A. Below 1

Explanation: A diamagnetic material has negative magnetic susceptibility, making its relative permeability slightly less than unity.

Q30. How many depletion layers does a bipolar junction transistor have?

A. Three
B. Two
C. One
D. Four

Correct Answer: B. Two

Explanation: The emitter–base and collector–base junctions each have a depletion region.

Q31. A 50 Hz induction motor operates at 2% slip. What is its rotor-current frequency?

A. 50 Hz
B. 25 Hz
C. 2 Hz
D. 1 Hz

Correct Answer: D. 1 Hz

Explanation: Rotor-current frequency equals slip multiplied by supply frequency:\[ f_r=sf=0.02\times50=1\ \text{Hz} \]

Q32. A 200 V DC shunt motor develops 54 N·m at an armature current of 10 A. What torque will it develop at 20 A?

A. 108 N·m
B. 54 N·m
C. 216 N·m
D. 27 N·m

Correct Answer: A. 108 N·m

Explanation: With approximately constant field flux, torque is proportional to armature current. Doubling the current doubles the torque:\[ T_2=54\times\frac{20}{10}=108\ \text{N·m} \]

Q33. A 400/200 V, 5 kVA transformer has 200 W core loss and 800 W full-load copper loss. At what load is efficiency maximum?

A. 5 kVA
B. 4 kVA
C. 3.5 kVA
D. 2.5 kVA

Correct Answer: D. 2.5 kVA

Explanation: Maximum efficiency occurs when copper loss equals core loss. If \(x\) is the fraction of full load:\[ x=\sqrt{\frac{200}{800}}=0.5 \]

Therefore, the required load is \(0.5\times5=2.5\) kVA.

Q34. Which power factors can a synchronous motor operate at?

A. Always lagging
B. Always leading
C. Leading, lagging or unity
D. Unity or lagging only

Correct Answer: C. Leading, lagging or unity

Explanation: Changing field excitation changes reactive-power demand, allowing operation at lagging, unity or leading power factor.

Q35. Why are dummy coils provided in a generator?

A. To decrease eddy-current loss
B. To increase flux density
C. To increase voltage
D. To maintain mechanical rotor balance

Correct Answer: D. To maintain mechanical rotor balance

Explanation: Dummy coils maintain mechanical balance without taking part in the electrical winding circuit.

Exam: Kerala PSC Electrical Engineer — Kerala State Cooperative Coir Marketing Federation Ltd, 7 June 2023

Q36. Which factors determine a battery’s capacity?

A. Plate size and number
B. Amount of active material
C. Amount of electrolyte
D. All three

Correct Answer: D. All three

Explanation: These construction factors influence how much charge the battery can deliver. Actual capacity also depends on operating conditions.

Exam: Kerala PSC Electrician / Overseer Grade I / Junior Instructor in Electrician, 30 September 2024
Paper: 129/2024, booklet A, original Q44

Q37. On which motor should Swinburne’s test not be performed?

A. DC shunt motor
B. DC series motor
C. Separately excited DC motor
D. It can be performed on every DC motor type

Correct Answer: B. DC series motor

Explanation: Swinburne’s is a no-load test. A DC series motor may accelerate dangerously when run without load.

Exam: Kerala PSC Electrician / Overseer Grade I / Junior Instructor in Electrician, 30 September 2024
Paper: 129/2024, booklet A, original Q69

Q38. How does the starting torque of a three-phase induction motor depend on supply voltage?

A. It is independent of voltage
B. It is directly proportional to voltage
C. It is directly proportional to voltage squared
D. None of these

Correct Answer: C. It is directly proportional to voltage squared

Explanation: At fixed frequency and machine parameters:\[ T_{\text{start}}\propto V^2 \]

A reduction in supply voltage therefore causes a larger proportional reduction in starting torque.

Exam: Kerala PSC Electrician / Overseer Grade I / Junior Instructor in Electrician, 30 September 2024
Paper: 129/2024, booklet A, original Q71

Q39. Which alternator type is used in a hydroelectric power station?

A. Non-salient-pole type
B. Turbo-generator
C. Steam turbine
D. Salient-pole type

Correct Answer: D. Salient-pole type

Explanation: Salient-pole alternators suit the comparatively low speeds of hydro turbines and can accommodate many poles.

Exam: Kerala PSC Electrician / Overseer Grade I / Junior Instructor in Electrician, 30 September 2024
Paper: 129/2024, booklet A, original Q75

Q40. All-day efficiency is especially useful for assessing which transformer?

A. Distribution transformer
B. Autotransformer
C. Power transformer
D. Two-winding transformer

Correct Answer: A. Distribution transformer

Explanation: A distribution transformer operates at varying loads throughout the day. Its 24-hour energy efficiency is therefore particularly useful.

Exam: Kerala PSC Electrician / Overseer Grade I / Junior Instructor in Electrician, 30 September 2024
Paper: 129/2024, booklet A, original Q76

Q41. In the two-wattmeter method, one meter reads zero and the other reads total power. What is the power factor?

A. 1
B. 0.5
C. Below 0.5
D. Zero

Correct Answer: B. 0.5

Explanation: For a balanced three-phase load, one wattmeter reads zero at a phase angle of \(60^\circ\):\[ \text{Power factor}=\cos60^\circ=0.5 \]

Exam: Kerala PSC Electrician/Lineman, 26 September 2025
Paper: 121/2025, booklet A, original Q62

Q42. Where is the oil-level indicator typically fitted on a distribution transformer?

A. Main tank
B. Conservator tank
C. Cooling tubes
D. Bushings

Correct Answer: B. Conservator tank

Explanation: For a conventional conservator-equipped transformer, the indicator shows the oil level in the conservator. This does not describe every sealed transformer design.

Exam: Kerala PSC Electrician/Lineman, 26 September 2025
Paper: 121/2025, booklet A, original Q67

Q43. Which listed factor improves LED-light performance?

A. Ferroresonance
B. Customisation
C. Utility factor
D. Thermal management

Correct Answer: D. Thermal management

Explanation: Effective heat removal limits LED junction temperature and supports light output and service life.

Exam: Kerala PSC Electrician/Lineman, 26 September 2025
Paper: 121/2025, booklet A, original Q73

Q44. What does COB stand for in electronics?

A. Chip on Board
B. Circuit on Board
C. Connection on Board
D. Capacitor on Board

Correct Answer: A. Chip on Board

Explanation: Chip-on-board construction mounts semiconductor chips directly on a board or substrate.

Exam: Kerala PSC Electrician/Lineman, 26 September 2025
Paper: 121/2025, booklet A, original Q74

Q45. What functions does the condenser perform in a steam power plant?

A. Maintains very low pressure at the turbine exhaust
B. Provides condensate that can be reused as boiler feedwater
C. Performs both A and B
D. Performs neither

Correct Answer: C. Performs both A and B

Explanation: Condensation maintains low turbine-exhaust pressure and recovers water for reuse in the steam cycle.

Exam: Kerala PSC Electrician/Lineman, 26 September 2025
Paper: 121/2025, booklet A, original Q85

Q46. Which panel-board device protects a motor against overload and overheating?

A. Rectifier
B. Limit switch
C. Thermal relay
D. Electromechanical relay

Correct Answer: C. Thermal relay

Explanation: A thermal overload relay trips after sustained excessive current, protecting the motor against overheating.

Exam: Kerala PSC Electrician-cum-Mechanic — Medical Education Department, 20 July 2023
Paper: 118/2023/OL, original Q25

Q47. What is the function of a moderator in a nuclear reactor?

A. Absorbing excess neutrons
B. Increasing neutron energy
C. Slowing neutrons
D. Slowing electrons

Correct Answer: C. Slowing neutrons

Explanation: A moderator reduces neutron energy. Control rods primarily absorb neutrons to control the chain reaction.

Exam: Kerala PSC Electrician-cum-Mechanic — Medical Education Department, 20 July 2023
Paper: 118/2023/OL, original Q29

Q48. Which controller is used for an eddy-current drive?

A. Slip controller
B. Rectifier controller
C. AC-voltage controller
D. DC-chopper controller

Correct Answer: A. Slip controller

Explanation: An eddy-current drive regulates output speed by controlling coupling excitation and slip.

Exam: Kerala PSC Electrician-cum-Mechanic — Medical Education Department, 20 July 2023
Paper: 118/2023/OL, original Q30

Q49. Which listed condition causes hunting in an alternator?

A. Operation with fluctuating speed
B. Overload
C. Continuous load fluctuations
D. No-load operation

Correct Answer: C. Continuous load fluctuations

Explanation: Load disturbances cause rotor oscillations about the synchronous operating position. These oscillations are known as hunting.

Exam: Kerala PSC Electrician-cum-Mechanic — Medical Education Department, 20 July 2023
Paper: 118/2023/OL, original Q40

Q50. Why must the load be disconnected before operating a transformer’s off-load tap changer?

A. To disconnect the taps from the neutral point
B. To disconnect the diverter’s moving contact
C. To prevent heavy sparking at the contacts
D. To electrically isolate the windings

Correct Answer: C. To prevent heavy sparking at the contacts

Explanation: Off-load contacts cannot safely interrupt load current. The transformer must be de-energised before operating its off-load tap changer.

Exam: Kerala PSC Electrician-cum-Mechanic — Medical Education Department, 20 July 2023
Paper: 118/2023/OL, original Q51

Quick Revision: Basic Electrical Engineering Facts

• A series RLC circuit is inductive above resonance.
• Maximum AC power transfer requires complex-conjugate impedance matching.
• For an equal-resistance delta, each equivalent star resistance is one-third of the delta value.
• A lead-acid cell has a nominal voltage of 2 V.
• A two-winding transformer works through mutual induction.
• A transformer preserves the supply frequency.
• Luminous efficacy is measured in lumens per watt.
• For a point source at unchanged incidence angle, illumination follows the inverse-square law.
• Induction-motor rotor frequency equals slip multiplied by supply frequency.
• At fixed frequency and machine parameters, induction-motor starting torque varies with voltage squared.
• Transformer maximum efficiency occurs when copper loss equals core loss.
• A synchronous motor can operate at lagging, unity or leading power factor.
• A DIAC commonly triggers a TRIAC.
• An SMPS supplies regulated DC power.
• A thermal overload relay protects a motor against sustained overload.
• A nuclear-reactor moderator slows neutrons.

Frequently Asked Questions

What are Basic Electrical Engineering PYQs?

They are questions actually asked in earlier examinations on topics such as circuits, electrical machines, transformers, measurements and electronics.

Which examinations are represented in this collection?

This article contains Kerala PSC questions from electrical recruitment examinations held during 2022–2025. The examination name, test date and paper code are stated below every question.

Are the answers verified?

Yes. The answers were checked against the final answer keys for the respective examinations.

Can these questions help with other electrical recruitment examinations?

Yes. Their concepts can support preparation for other electrical recruitment examinations. Check your target syllabus separately; usefulness for preparation does not mean these questions appeared in those other examinations.

Which formulas should I revise alongside these questions?

Start with Ohm’s law, electrical power, reactance, star–delta conversion, magnetic field strength, motor slip, rotor frequency, torque relationships and transformer losses. Practise calculations and understand the assumptions behind each formula.

Are these ordinary practice questions or genuine previous year questions?

They are verified previous year questions, lightly paraphrased for clear English. Original option meanings and numerical data are preserved.

Try solving the following PYQs for Basic Electrical Engineering to improve your calculation skills, concept learning and know what concepts you should revise. Solve the questions and after that go through the answers along with their explanations.