Electrical Engineering Diploma Interview Questions & Answers | EngineerX
Electrical Engineering (Diploma / Polytechnic) Interview Questions & Answers — commonly asked polytechnic diploma interview and campus placement questions with clear, practical answers. Tap any question to open its answer.
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Electrical Engineering — Diploma Interview Q&A
Q1What is Electrical Engineering?
AnswerElectrical Engineering deals with the generation, transmission, distribution, control and utilization of electrical energy. It also covers electrical machines, power systems, protection, control systems, instrumentation and industrial electrical equipment.
Q2What is electric charge?
AnswerElectric charge is a fundamental property of matter responsible for electrical effects. It can be positive or negative, and its SI unit is coulomb (C). The movement of electric charge produces electric current.
Q3What is voltage?
AnswerVoltage is the electrical potential difference between two points. It provides the driving force that causes current to flow through a circuit when a conductive path exists. Its SI unit is volt (V).
Q4What is electric current?
AnswerElectric current is the rate of flow of electric charge through a conductor. It is represented by I and its SI unit is ampere (A). Mathematically, I = Q/t.
Q5What is resistance?
AnswerResistance is the opposition offered by a material or component to the flow of electric current. Its SI unit is ohm (ฮฉ). Resistance depends on factors such as material, length, cross-sectional area and temperature.
Q6State Ohm's Law.
AnswerOhm's Law states that, under constant physical conditions, current through a conductor is directly proportional to the voltage across it. The relationship is V = IR, where V is voltage, I is current and R is resistance.
Q7What is electrical power?
AnswerElectrical power is the rate at which electrical energy is generated, transferred or consumed. Its SI unit is watt (W). In a DC circuit, power can be calculated as P = VI.
Q8What is electrical energy?
AnswerElectrical energy is the amount of electrical work performed or energy consumed over a period of time. It can be calculated as E = Pt. Commercial electrical energy is commonly measured in kilowatt-hours (kWh), also called units.
Q9What is the difference between power and energy?
AnswerPower represents the rate of energy transfer or consumption, while energy represents the total amount transferred or consumed over time. For example, a 1 kW heater operating for 2 hours consumes 2 kWh of energy.
Q10What is the difference between AC and DC?
AnswerDC, or direct current, flows in one direction and normally has constant polarity. AC, or alternating current, periodically changes magnitude and direction. Batteries provide DC, while utility power supplied to homes and industries is generally AC.
Q11What is frequency in an AC system?
AnswerFrequency is the number of complete cycles of an alternating waveform per second. Its unit is hertz (Hz). In India, the standard utility AC frequency is 50 Hz.
Q12What is the time period of an AC waveform?
AnswerTime period is the time required to complete one complete cycle of an AC waveform. It is represented by T and is related to frequency by T = 1/f. For a 50 Hz waveform, the time period is 20 ms.
Q13What is RMS value of AC?
AnswerRMS stands for Root Mean Square. It represents the equivalent DC value that would produce the same heating effect in a resistor. For a pure sinusoidal waveform, Vrms = Vmax/√2.
Q14What is peak value of an AC waveform?
AnswerPeak value is the maximum instantaneous value reached by an alternating voltage or current during a cycle. For a sinusoidal waveform, peak voltage is related to RMS voltage by Vmax = √2 × Vrms.
Q15What is peak-to-peak voltage?
AnswerPeak-to-peak voltage is the difference between the maximum positive and maximum negative values of a waveform. For a symmetrical sine wave, Vpp = 2Vmax.
Q16What is impedance?
AnswerImpedance is the total opposition offered by an AC circuit to current flow. It includes resistance and reactance and is measured in ohms. It is represented by Z.
Q17What is reactance?
AnswerReactance is the opposition offered to AC current by inductors and capacitors. Inductive reactance is XL = 2ฯfL, while capacitive reactance is XC = 1/(2ฯfC).
Q18What is inductance?
AnswerInductance is the property of a coil that opposes changes in current by producing an induced voltage. Its SI unit is henry (H). Inductors store energy in their magnetic field.
Q19What is capacitance?
AnswerCapacitance is the ability of a component or system to store electric charge. Its SI unit is farad (F). Capacitors store energy in an electric field.
Q20What is the function of a resistor in an electrical circuit?
AnswerA resistor limits current and produces a voltage drop when current flows through it. It is used for current control, voltage division, protection and circuit biasing. Electrical heating elements also use resistance to convert electrical energy into heat.
Q21What are Kirchhoff's Laws?
AnswerKirchhoff's Laws are fundamental circuit-analysis principles. Kirchhoff's Current Law (KCL) is based on conservation of charge, while Kirchhoff's Voltage Law (KVL) is based on conservation of energy.
Q22State Kirchhoff's Current Law (KCL).
AnswerKCL states that the algebraic sum of currents at a node is zero. In practical terms, the total current entering a junction must equal the total current leaving it.
Q23State Kirchhoff's Voltage Law (KVL).
AnswerKVL states that the algebraic sum of all voltages around any closed electrical loop is zero. In other words, the total voltage rises equal the total voltage drops around a closed loop.
Q24What is a series circuit?
AnswerIn a series circuit, components are connected along a single current path. Therefore, the same current flows through all components, while the supply voltage is divided among them according to their impedances or resistances.
Q25What is a parallel circuit?
AnswerIn a parallel circuit, components are connected across the same two electrical nodes. Therefore, the voltage across each branch is the same, while the total current is the sum of the branch currents.
Q26What happens to total resistance when resistors are connected in series?
AnswerThe total resistance increases and is equal to the sum of individual resistances: Rtotal = R1 + R2 + R3 + .... Therefore, series resistance can be used to limit current.
Q27What happens to total resistance when resistors are connected in parallel?
AnswerThe equivalent resistance becomes lower than the smallest individual resistance. For two resistors, Req = R1R2/(R1 + R2). Parallel connections are commonly used when multiple loads need to operate across the same voltage.
Q28What is a short circuit?
AnswerA short circuit occurs when two points having a voltage difference become connected through a very low-resistance path. This can cause a very high current, which may damage equipment and create fire or safety hazards.
Q29What is an open circuit?
AnswerAn open circuit is a circuit in which the conducting path is interrupted. Ideally, no current flows through the open portion even though voltage may exist across it.
Q30What is a fuse?
AnswerA fuse is an overcurrent protection device containing a fusible element that melts when excessive current flows for sufficient time. It interrupts the circuit and protects wiring and equipment from excessive current.
Q31What is an MCB?
AnswerMCB stands for Miniature Circuit Breaker. It automatically disconnects a circuit during conditions such as overload or short circuit and can normally be reset after the fault is cleared.
Q32What is the difference between a fuse and an MCB?
AnswerA fuse operates by melting its element and generally must be replaced after operation. An MCB uses a mechanical tripping mechanism and can normally be reset. Both provide overcurrent protection, but their characteristics and applications differ.
Q33What is an RCCB?
AnswerRCCB stands for Residual Current Circuit Breaker. It detects an imbalance between current flowing through the live and neutral conductors, indicating leakage to earth, and trips the circuit to provide protection against electric shock and certain leakage-related hazards.
Q34What is earthing?
AnswerEarthing is the intentional connection of exposed conductive parts or specified electrical system points to earth through a suitable low-impedance path. It helps control fault voltages and provides a path for fault current so protective devices can operate.
Q35Why is earthing important?
AnswerEarthing improves electrical safety by reducing dangerous touch voltages during insulation faults. It also provides a suitable path for fault current, helping protective devices disconnect the faulty circuit.
Q36What is the difference between earthing and grounding?
AnswerThe terms are sometimes used interchangeably, but technically they can have different meanings depending on the system. Earthing commonly refers to connecting exposed conductive parts to earth for safety, while grounding can also refer to connecting a circuit or system point to a reference or earth.
Q37What is a single-phase supply?
AnswerA single-phase AC system generally uses one alternating voltage waveform between the phase and neutral conductors. It is commonly used for residential lighting, fans, small appliances and other relatively low-power loads.
Q38What is a three-phase supply?
AnswerA three-phase system consists of three AC voltages of the same frequency and magnitude separated by approximately 120 electrical degrees. It is widely used in industrial power systems because it provides efficient power transmission and is well suited for motors.
Q39What is the advantage of three-phase power over single-phase power?
AnswerThree-phase systems can transmit a given amount of power efficiently with less conductor material compared with equivalent single-phase arrangements. They also provide a naturally rotating magnetic field that is highly useful for operating AC motors.
Q40What are star and delta connections?
AnswerStar, or Y, connection joins one end of each of three phase windings at a common neutral point. Delta, or ฮ, connection connects the windings end-to-end to form a closed loop. Both are widely used in three-phase systems and motors.
Q41What is power factor?
AnswerPower factor is the ratio of real power to apparent power in an AC circuit. For a sinusoidal system, it is commonly expressed as PF = cosฯ, where ฯ is the phase angle between voltage and current.
Q42Why is low power factor undesirable?
AnswerFor a given real power, a lower power factor requires higher current. Higher current causes increased losses and voltage drops and may require larger electrical equipment and conductors. Improving power factor can therefore improve system utilization.
Q43How can power factor be improved?
AnswerIn industrial systems with inductive loads, power factor is commonly improved using appropriately sized capacitor banks or other power-factor correction equipment. The correction system should be properly designed to avoid overcompensation and resonance problems.
Q44What is an electrical load?
AnswerAn electrical load is a device or system that consumes electrical power. Examples include motors, heaters, lamps, pumps, compressors and electronic equipment.
Q45What is an inductive load?
AnswerAn inductive load contains significant inductance and causes current to lag voltage in a sinusoidal steady-state circuit. Motors, transformers and many electromagnetic devices are common examples.
Q46What is a capacitive load?
AnswerA capacitive load has significant capacitance and causes current to lead voltage in an AC circuit. Capacitor banks used for power-factor correction are common examples.
Q47What is a transformer?
AnswerA transformer is a static electrical device that transfers AC electrical energy from one circuit to another through electromagnetic induction. It can increase or decrease voltage and can also provide electrical isolation.
Q48What is the working principle of a transformer?
AnswerA transformer works on the principle of mutual electromagnetic induction. Alternating current in the primary winding produces changing magnetic flux in the core, which induces an EMF in the secondary winding.
Q49What is the difference between a step-up and step-down transformer?
AnswerA step-up transformer increases the secondary voltage relative to the primary voltage and generally has more turns on the secondary winding. A step-down transformer reduces the secondary voltage and generally has fewer secondary turns.
Q50Why does a transformer work on AC but not on steady DC?
AnswerTransformer operation requires changing magnetic flux to induce voltage in the secondary winding. Steady DC does not continuously change the magnetic flux after the initial transient, so normal transformer action does not occur. Applying DC can cause excessive primary current and overheating.
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