Practical Viva Questions and Answers of Fundamental of Electrical and Electrical Engineering

skygyanweb May 23, 2025 0

Here are few questions and answers which can be asked in Practical viva-

1. Q: What is an electrical circuit?
A: An electrical circuit is a closed loop of conductive material through which electric current can flow. It typically includes a voltage source, conductors, and a load (like a resistor or LED).

2. Q: What is the difference between a conductor and an insulator?
A: A conductor allows the flow of electric current easily (e.g., copper), while an insulator resists the flow of current (e.g., rubber).

3. Q: What is Ohm’s Law?
A: Ohm’s Law states that the current through a conductor is directly proportional to the voltage across it, provided the temperature remains constant.
Formula: V=IRV = IRV=IR

4. Q: What are the types of resistors?
A: Fixed resistors, variable resistors (potentiometers), thermistors, and LDRs (Light Dependent Resistors).

5. Q: What is a capacitor?
A: A capacitor is a two-terminal passive component that stores electrical energy in an electric field. It resists changes in voltage.

6. Q: What is the unit of capacitance?
A: Farad (F)

7. Q: What is a diode?
A: A diode is a semiconductor device that allows current to flow in one direction only.

8. Q: What is the function of a rectifier?
A: A rectifier converts AC (alternating current) to DC (direct current).

9. Q: What is the difference between NPN and PNP transistors?
A: In NPN transistors, current flows from collector to emitter when a positive voltage is applied to the base. In PNP transistors, current flows from emitter to collector with a negative base voltage.

10. Q: What is a relay?
A: A relay is an electromechanical switch that uses an electromagnet to open or close contacts in a circuit.

11. Q: What is the difference between analog and digital signals?
A: Analog signals are continuous and vary with time, while digital signals have only two levels—high (1) and low (0).

12. Q: What is a multimeter?
A: A multimeter is an electronic measuring instrument that can measure voltage, current, and resistance.

1. Q: What is Digital Electronics?
A: Digital electronics deals with circuits that operate using digital signals (0s and 1s) rather than continuous analog signals.

2. Q: What is the difference between Analog and Digital signals?
A:

  • Analog: Continuous and variable signals.
  • Digital: Discrete signals (usually binary: 0 and 1).

3. Q: Define Logic Gate.
A: A logic gate is a digital circuit that performs a logical operation on one or more binary inputs and gives a single binary output.

4. Q: What are the basic logic gates?
A: AND, OR, and NOT gates.

5. Q: What are universal gates?
A: NAND and NOR gates are called universal gates because any logic gate can be built using them.

6. Q: What is the function of a NOT gate?
A: It inverts the input.
If input = 1, output = 0; if input = 0, output = 1.

7. Q: What is a flip-flop?
A: A flip-flop is a basic memory element in digital electronics that stores one bit of data.

8. Q: Types of Flip-Flops?
A: SR, JK, D, and T flip-flops.

9. Q: What is the function of a Multiplexer (MUX)?
A: A multiplexer selects one input from multiple inputs and forwards it to a single output line based on select lines.

10. Q: What is a Demultiplexer (DEMUX)?
A: It takes a single input and channels it to one of the many outputs based on select lines.

11. Q: What is the difference between a latch and a flip-flop?
A:

  • Latch: Level-triggered (changes with input level).
  • Flip-flop: Edge-triggered (changes on clock pulse edges).

12. Q: What is a counter?
A: A counter is a sequential circuit that counts clock pulses, used in timers, clocks, etc.

13. Q: What is the difference between synchronous and asynchronous counters?
A:

  • Synchronous: All flip-flops triggered by the same clock.
  • Asynchronous: Flip-flops triggered by different clocks (ripple effect).

14. Q: What is a Register?
A: A register is a group of flip-flops used to store multi-bit binary data.

15. Q: What is Boolean Algebra?
A: A mathematical method to simplify digital logic expressions using binary variables and logic operations.

16. Q: What is the purpose of Karnaugh Map (K-Map)?
A: K-Map is used to simplify Boolean expressions by minimizing logic functions easily.

17. Q: What is propagation delay?
A: The time taken by a signal to travel from input to output of a logic gate.

18. Q: What is fan-in and fan-out?
A:

  • Fan-in: Number of inputs to a gate.
  • Fan-out: Number of gate inputs a gate’s output can drive.

19. Q: What are combinational circuits?
A: Circuits whose output depends only on the current inputs (e.g., adders, multiplexers).

20. Q: What are sequential circuits?
A: Circuits whose output depends on both current input and past input (history), using memory elements (e.g., flip-flops, counters).

1. Q: What is the difference between electrical and electronics?
A:

  • Electrical: Deals with high voltage and current (AC), like motors and generators.
  • Electronics: Deals with low voltage and current (DC), like transistors and ICs.

2. Q: Define current, voltage, and resistance.
A:

  • Current (I): Flow of electric charge, measured in amperes (A).
  • Voltage (V): Potential difference between two points, measured in volts (V).
  • Resistance (R): Opposition to current flow, measured in ohms (Ω).

3. Q: State Ohm’s Law.
A:
Ohm’s Law states that current is directly proportional to voltage and inversely proportional to resistance.
Formula: V=IRV = IRV=IR

4. Q: What is the unit of power?
A: Watt (W).
Formula: P=VIP = VIP=VI

5. Q: What is AC and DC?
A:

  • AC (Alternating Current): Changes direction periodically.
  • DC (Direct Current): Flows in one direction only.

6. Q: What is the frequency of AC supply in India?
A: 50 Hz.

7. Q: What are the types of electrical circuits?
A:

  • Series Circuit: Components connected end-to-end.
  • Parallel Circuit: Components connected across the same voltage.

8. Q: What is a fuse?
A: A protective device that melts and breaks the circuit when current exceeds safe levels.

9. Q: What is a circuit breaker?
A: An automatically operated switch that protects a circuit from damage due to overload or short circuit.

10. Q: What is a transformer?
A: A device that increases or decreases AC voltage using electromagnetic induction.

11. Q: What is the principle of a transformer?
A: Mutual induction.

12. Q: What are the main parts of a transformer?
A: Core, primary winding, and secondary winding.

13. Q: What is earthing?
A: Connecting the non-current carrying parts of electrical equipment to the ground for safety.

14. Q: What is the difference between a generator and a motor?
A:

  • Generator: Converts mechanical energy into electrical energy.
  • Motor: Converts electrical energy into mechanical energy.

15. Q: What is the function of a capacitor in an electrical circuit?
A: Stores electrical energy, improves power factor, and filters AC signals.

16. Q: What is power factor?
A: Ratio of real power to apparent power.
Formula: Power Factor=cos⁡(ϕ)\text{Power Factor} = \cos(\phi)Power Factor=cos(ϕ)

17. Q: What is the ideal power factor?
A: 1 (or unity), meaning all power is effectively used.

18. Q: What is a relay?
A: An electrically operated switch used to control a circuit.

19. Q: What is the difference between single-phase and three-phase supply?
A:

  • Single-phase: One AC voltage waveform.
  • Three-phase: Three AC waveforms, 120° apart, used for heavy loads.

20. Q: What is an inductor?
A: A passive component that stores energy in the form of a magnetic field and opposes sudden changes in current.

1. Q: What is measurement?
A: Measurement is the process of determining the magnitude of a quantity by comparing it with a standard unit.

2. Q: What are the types of measurement?
A:

  • Direct Measurement: Comparing directly with a standard.
  • Indirect Measurement: Obtained using formulas or instruments (e.g., measuring power using voltage and current).

3. Q: What is an instrument?
A: An instrument is a device used to measure, display, or record physical quantities like voltage, current, resistance, etc.

4. Q: What is the difference between accuracy and precision?
A:

  • Accuracy: Closeness to the true value.
  • Precision: Repeatability or consistency of results.

5. Q: What is sensitivity of an instrument?
A: The ratio of the change in output to the change in input. It indicates how responsive the instrument is.

6. Q: What is a multimeter?
A: A multimeter is an electronic measuring instrument that combines voltmeter, ammeter, and ohmmeter in one unit.

7. Q: What is least count?
A: The smallest value that an instrument can measure or read accurately.

8. Q: What is a transducer?
A: A device that converts one form of energy into another (e.g., a thermocouple converts heat into voltage).

9. Q: What are analog and digital instruments?
A:

  • Analog: Show continuous values using pointers (e.g., analog voltmeter).
  • Digital: Show discrete numeric values (e.g., digital multimeter).

10. Q: What is the role of calibration?
A: Calibration is the process of setting or correcting an instrument to ensure its readings are accurate.

11. Q: What is an ammeter?
A: An instrument used to measure electric current, connected in series with the circuit.

12. Q: What is a voltmeter?
A: A device used to measure voltage, connected in parallel with the circuit.

13. Q: What is a wattmeter?
A: An instrument used to measure power in an electrical circuit.

14. Q: What is the function of a galvanometer?
A: A sensitive instrument used to detect and measure small electric currents.

15. Q: Define range and span.
A:

  • Range: The minimum to maximum value an instrument can measure.
  • Span: The difference between the maximum and minimum value.

16. Q: What are the types of errors in measurement?
A:

  • Systematic Error: Due to instrument or environment.
  • Random Error: Due to unknown and unpredictable factors.
  • Gross Error: Due to human mistakes.

17. Q: What is loading effect?
A: When the measuring instrument draws energy from the circuit and affects the measured value.

18. Q: What is the main purpose of measurement systems?
A: To monitor, control, and analyze physical systems accurately.

19. Q: What is the difference between active and passive transducers?
A:

  • Active: Require no external power (e.g., thermocouple).
  • Passive: Require external power (e.g., strain gauge).

20. Q: What is the SI unit of:

  • Voltage? → Volt (V)
  • Current? → Ampere (A)
  • Resistance? → Ohm (Ω)
  • Power? → Watt (W)

1. Q: What is an electric circuit?
A: An electric circuit is a closed path in which current flows due to a voltage source.

2. Q: What is Ohm’s Law?
A:
Ohm’s Law states that current is directly proportional to voltage and inversely proportional to resistance:
V = IR

3. Q: What is resistance?
A: Resistance is the property of a material that opposes the flow of electric current, measured in ohms (Ω).

4. Q: What is conductance?
A: Conductance is the reciprocal of resistance and is measured in siemens (S).
G = 1/R

5. Q: What are the types of electric circuits?
A:

  • Series Circuit
  • Parallel Circuit
  • Series-Parallel Circuit

6. Q: Define power and energy in electrical terms.
A:

  • Power (P) = V × I, measured in Watts (W).
  • Energy (E) = Power × Time, measured in joules (J) or kilowatt-hours (kWh).

🧲 Magnetic Circuit Questions

7. Q: What is a magnetic circuit?
A: A magnetic circuit is the closed path followed by magnetic flux, analogous to an electric circuit.

8. Q: What is magnetic flux?
A: Magnetic flux is the total number of magnetic field lines passing through a given area, measured in Webers (Wb).

9. Q: What is flux density?
A: Flux density (B) is magnetic flux per unit area, measured in Weber/m² or Tesla (T).
B = Φ / A

10. Q: What is magnetomotive force (MMF)?
A: MMF is the magnetic pressure that drives magnetic flux, similar to EMF in electric circuits.
MMF = NI (N = turns, I = current)

11. Q: What is reluctance?
A: Reluctance is the opposition offered by a material to magnetic flux, similar to resistance in electrical circuits.
Reluctance (ℜ) = l / (μA)

12. Q: What is permeability?
A: Permeability (μ) is the ability of a material to allow the formation of magnetic lines of force.

13. Q: Compare electric and magnetic circuits.

Electric CircuitMagnetic Circuit
Current flowsFlux flows
EMF (V)MMF (NI)
Resistance (R)Reluctance (ℜ)
Conductors (Cu, Al)Ferromagnetic materials

14. Q: What is hysteresis?
A: Hysteresis is the lag between magnetization and the applied magnetic field, causing energy loss in the form of heat.

15. Q: What is magnetic saturation?
A: Magnetic saturation is the state where an increase in MMF does not significantly increase magnetic flux.

16. Q: What is a B-H curve?
A: It is a graph of magnetic flux density (B) versus magnetic field strength (H), showing the magnetization characteristics of materials.

17. Q: What is eddy current loss?
A: Loss due to circulating currents induced in the core when exposed to a changing magnetic field.

18. Q: How is magnetic flux measured?
A: Using a flux meter or calculated using Φ = B × A.

19. Q: What are the types of magnetic materials?
A:

  • Ferromagnetic (e.g., iron)
  • Paramagnetic
  • Diamagnetic

20. Q: How are magnetic and electric quantities related?

Electric QuantityMagnetic Quantity
Voltage (V)MMF (NI)
Current (I)Flux (Φ)
Resistance (R)Reluctance (ℜ)

1. Q: What is a transformer?
A: A transformer is a static device that transfers electrical energy between two or more circuits through electromagnetic induction.

2. Q: What is the principle of a transformer?
A: Mutual induction between two windings.

3. Q: Name the main parts of a transformer.
A: Core, primary winding, secondary winding, insulation, tank, conservator, breather.

4. Q: What is the function of a transformer?
A: To step up or step down the AC voltage level without changing the frequency.

5. Q: Why are transformers rated in kVA, not kW?
A: Because transformer losses depend on voltage and current (not on power factor), and kVA = V × I.

6. Q: What are the types of transformers?
A:

  • Step-up and Step-down
  • Power transformer and Distribution transformer
  • Single-phase and Three-phase

7. Q: What is no-load and full-load condition in a transformer?
A:

  • No-load: Secondary is open.
  • Full-load: Transformer supplies rated load.

8. Q: What are losses in a transformer?
A:

  • Core loss: Hysteresis + Eddy current loss
  • Copper loss: I²R loss in windings

9. Q: What is efficiency of a transformer?
A:
Efficiency = (Output power / Input power) × 100%
Usually around 95%–99%

10. Q: What is voltage regulation?
A: It is the change in secondary voltage from no-load to full-load, expressed as a percentage of full-load voltage.

⚙️ B. Electrical Machines

🌀 1. DC Machines

11. Q: What are the types of DC machines?
A:

  • DC Generator
  • DC Motor
    Each can be: Shunt, Series, or Compound

12. Q: What is the principle of a DC generator?
A: Electromagnetic induction (Faraday’s Law).

13. Q: What is the function of a commutator in a DC machine?
A: It converts AC induced in armature to DC at the output terminals.

14. Q: What is back EMF in DC motors?
A: The EMF induced in the armature that opposes the applied voltage.

15. Q: What is the function of brushes in a DC machine?
A: To provide electrical contact between rotating commutator and external circuit.

⚡ 2. AC Machines

16. Q: Types of AC machines?
A:

  • Synchronous machines
  • Induction machines

17. Q: What is an induction motor?
A: An AC motor in which rotor rotates due to induced EMF, without physical connection to stator.

18. Q: What is slip in an induction motor?
A:
Slip = ((Ns − Nr)/Ns) × 100
Where Ns = Synchronous speed, Nr = Rotor speed

19. Q: Why is the induction motor called an asynchronous motor?
A: Because the rotor speed is not equal to the synchronous speed.

20. Q: What is the use of a synchronous motor?
A: Used where constant speed is required, e.g., in clocks, compressors, conveyors.

🔹 1. Q: What is an AC circuit?

A:
An AC (Alternating Current) circuit is an electrical circuit in which the current changes direction periodically. The voltage also reverses because the current changes direction.

🔹 2. Q: What is the frequency of AC supply in India?

A:
50 Hz (Hertz), meaning the current completes 50 cycles per second.

🔹 3. Q: What is the form of AC voltage?

A:
A sinusoidal waveform is the most common form of AC voltage.

🔹 4. Q: Define RMS value of AC.

A:
The RMS (Root Mean Square) value is the effective value of AC voltage or current, equivalent to the DC value that would produce the same heating effect.

🔹 5. Q: What is the average value of a sine wave over one complete cycle?

A:
Zero, because the positive and negative halves cancel each other.

🔹 6. Q: Define peak value.

A:
The maximum value (positive or negative) of AC voltage or current.

🔹 7. Q: What is the power factor?

A:
Power factor = Cos(ϕ)
It is the cosine of the phase angle between voltage and current in an AC circuit.

🔹 8. Q: What is the ideal power factor?

A:
1 or unity, which indicates maximum efficiency and no reactive power.

🔹 9. Q: What are the types of loads in AC circuits?

A:

  • Resistive (e.g., heater)
  • Inductive (e.g., motor)
  • Capacitive (e.g., capacitor bank)

🔹 10. Q: What is a phasor?

A:
A phasor is a rotating vector that represents a sinusoidal quantity having magnitude and phase.

🔹 11. Q: What is impedance?

A:
The total opposition to AC, including resistance and reactance:
Z = √(R² + (X_L – X_C)²)

🔹 12. Q: What is the difference between resistance, inductive reactance, and capacitive reactance?

A:

  • Resistance (R): Opposes both AC and DC.
  • Inductive Reactance (X_L = 2πfL): Opposes change in current.
  • Capacitive Reactance (X_C = 1 / (2πfC)): Opposes change in voltage.

🔹 13. Q: What is resonance in an AC circuit?

A:
Resonance occurs when inductive reactance = capacitive reactance (X_L = X_C). The circuit behaves purely resistive, and current is maximum.

🔹 14. Q: What is the significance of phase angle (ϕ) in AC?

A:
It represents the time difference between voltage and current waveforms.

🔹 15. Q: What is reactive power?

A:
The power that oscillates between source and reactive components (L and C), measured in VAR (Volt-Ampere Reactive).

🔹 16. Q: What is apparent power?

A:
The product of RMS voltage and current:
S = V × I (in VA)

🔹 17. Q: What is true or active power?

A:
The actual power consumed:
P = VIcosϕ (in Watts)

🔹 18. Q: What is a power triangle?

A:
A graphical representation of the relationship between active power, reactive power, and apparent power.

🔹 19. Q: What is the phase relationship in:

  • Resistive circuit → Voltage and current are in phase
  • Inductive circuit → Current lags voltage
  • Capacitive circuit → Current leads voltage

🔹 20. Q: Why is AC preferred over DC for transmission?

A:

  • Easy to transform voltage levels
  • Less transmission losses
  • Can be generated and distributed more economically

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