Electrical engineering interviews usually test two things, your basic concepts and your practical understanding. Since you are an electrical engineer and still in college, most questions will focus on fundamentals, machines, power systems, and a bit of real world application.

Part 1: Core Fundamentals & Theory

1. What is the difference between Real, Reactive, and Apparent power?
   • Answer: Real power (P) performs work (Watts). Reactive power (Q) sustains magnetic fields in inductive/capacitive loads (VAR). Apparent power (S) is the vector sum of both (VA), calculated as $$S = \sqrt{P^2 + Q^2}$$
2. Define Power Factor. Why is a low power factor a problem?
   • Answer: Power factor is the ratio of real power to apparent power (cos φ). A low power factor means more current is drawn for the same amount of work, leading to higher energy losses and potential penalties from utilities.
3. Explain Ohm’s Law and its limitations.
   • Answer: V = IR. It states voltage is proportional to current in a conductor. It doesn’t apply to non-ohmic devices like semiconductors (diodes, transistors) or where temperature varies significantly.
4. What is Kirchoff’s Current Law (KCL)?
   • Answer: The sum of currents entering a junction equals the sum of currents leaving it (Conservation of Charge).
5. What is Kirchoff’s Voltage Law (KVL)?
   • Answer: The sum of all electromotive forces and voltage drops in a closed loop is zero (Conservation of Energy).
6. What is a capacitor, and how does it behave in DC vs. AC circuits?
   • Answer: A capacitor stores energy in an electric field. In DC, it acts as an open circuit once charged. In AC, it allows current to flow but creates a phase shift where current leads voltage.
7. What is an inductor, and how does it behave in DC vs. AC circuits?
   • Answer: An inductor stores energy in a magnetic field. In DC, it acts as a short circuit (after the initial transient). In AC, it opposes changes in current, causing voltage to lead current.
8. What is Thevenin’s Theorem?
   • Answer: Any linear circuit with voltage sources and resistances can be replaced by a single voltage source ($V_{th}$) in series with a single resistor ($R_{th}$).
9. What is the difference between a BJT and a MOSFET?
   • Answer: A BJT (Bipolar Junction Transistor) is current-controlled. A MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) is voltage-controlled and generally more efficient for switching.
10. Explain the skin effect.
    • Answer: In AC, current tends to flow near the surface (the “skin”) of a conductor. This increases the effective resistance at higher frequencies.

Part 2: Power Systems & Machines

11. How does a transformer work?
    • Answer: It transfers electrical energy between circuits through electromagnetic induction via a shared magnetic core.

12. Why is power transmitted at high voltages?
    • Answer: To reduce I2R (heat) losses. Higher voltage allows for lower current to transmit the same amount of power.
13. What is the difference between a 1-phase and 3-phase system?
    • Answer: 1-phase uses two wires (live and neutral). 3-phase uses three AC voltages shifted by 120°, providing more constant power delivery and higher efficiency for industrial motors.
14. What is a VFD (Variable Frequency Drive)?
    • Answer: A device that controls the speed of an AC motor by varying the frequency and voltage of the power supplied to it.
15. Explain the purpose of a protective relay.
    • Answer: It detects abnormal conditions (like faults) and signals a circuit breaker to trip, isolating the fault to prevent equipment damage.
16. What is “Star” (Wye) vs. “Delta” connection?
    • Answer: Star has a common neutral point; Delta is a closed-loop with no neutral. Star is common for distribution (to get two voltage levels), while Delta is used for heavy industrial loads.
17. What is a “Short Circuit”?
    • Answer: An abnormal low-resistance path between two points of different potential, resulting in an excessive flow of current.
18. Explain the working of an Induction Motor.
    • Answer: Stator windings create a rotating magnetic field that induces a current in the rotor. This rotor current creates its own field, which interacts with the stator field to produce torque.
19. What is “Slip” in an induction motor?
    • Answer: The difference between the synchronous speed (magnetic field speed) and the actual rotor speed.
20. What is a UPS (Uninterruptible Power Supply)?
    • Answer: A system that provides near-instantaneous emergency power from batteries when the main input power source fails.

Part 3: Practical & Behavioral

21. What are the common safety precautions when working on live circuits?
    • Answer: Using PPE (gloves, mats), following LOTO (Lock Out, Tag Out) procedures, using insulated tools, and working with a “buddy” when possible.
22. What is a PLC, and where is it used?
    • Answer: A Programmable Logic Controller. It is a ruggedized computer used for industrial automation to control manufacturing processes.
23. How do you troubleshoot a circuit that has stopped working?
    • Answer: Start with a visual inspection, check the power source, test fuses/breakers, and then use a multimeter to trace the voltage at various nodes until the drop is found.
24. What is the difference between a Fuse and a Circuit Breaker?
    • Answer: A fuse melts and must be replaced; a circuit breaker trips and can be reset.
25. Explain “Earthing” or “Grounding.”
    • Answer: Connecting the non-current carrying parts of equipment to the earth to provide a safe path for fault current, preventing electric shocks.
26. What is Harmonic Distortion?
    • Answer: Pollution of the electrical wave caused by non-linear loads (like computers or VFDs) that can cause overheating and equipment malfunction.
27. What software are you proficient in for EE?
    • Answer: (Personalize this) Mention tools like AutoCAD, MATLAB/Simulink, ETAP, PSpice, or Revit.
28. How do you handle a situation where a project is falling behind schedule?
    • Answer: Identify the bottleneck, communicate with stakeholders early, prioritize “critical path” tasks, and re-allocate resources if possible.
29. What are “No-load” losses in a transformer?
    • Answer: Losses that occur even when no load is connected, primarily due to hysteresis and eddy currents in the iron core (Core Losses).
30. Describe a time you solved a difficult technical problem.
    • Answer: (Use the STAR method: Situation, Task, Action, Result. Focus on your logic and the specific technical steps you took.)