১০০ টা গুরুত্বপূর্ণ ভাইভা প্রশ্ন ও উত্তর

1. What is Ohm's law? Answer: Ohm's law states that the current through a conductor between two points is directly proportional to the voltage across the two points and inversely proportional to the resistance.

2. Define a diode. Answer: A diode is a two-terminal semiconductor device that allows current to flow in one direction only.

3. What is the difference between an analog and a digital signal? Answer: An analog signal is continuous and takes on any value within a given range, while a digital signal is discrete and represented by binary digits (0s and 1s).

4. What are the three essential parts of a power system? Answer: The three essential parts of a power system are generation, transmission, and distribution.

5. Explain the purpose of a transformer in the power system. Answer: Transformers are used to step up or step down voltage levels in the power system for efficient transmission and distribution of electrical energy.

6. What is the difference between a fuse and a circuit breaker? Answer: A fuse is a one-time use device that melts when current exceeds a certain value, breaking the circuit. A circuit breaker is a reusable device that trips when excessive current flows through it.

7. What is a capacitor used for? Answer: A capacitor is used to store and release electrical energy, smoothing out voltage fluctuations in a circuit.

8. How does a three-phase system differ from a single-phase system? Answer: A three-phase system has three conductors and provides higher power capacity compared to a single-phase system, which has only one conductor.

9. Explain the working principle of a DC motor. Answer: A DC motor converts electrical energy into mechanical energy through the interaction of magnetic fields in the motor's armature and field windings.

10. What is the purpose of a rectifier in an electronic circuit? Answer: A rectifier converts an alternating current (AC) into a direct current (DC) by allowing current flow in only one direction.

11. What is the difference between resistance and impedance? Answer: Resistance is a measure of opposition to the flow of current in a DC circuit, while impedance includes both resistance and reactance and is used in AC circuits.

12. What is the unit of electrical power? Answer: The unit of electrical power is the watt (W).

13. What is the function of a transistor in an electronic circuit? Answer: Transistors are semiconductor devices used to amplify or switch electronic signals and power.

14. Explain the concept of ground in electrical circuits. Answer: Ground serves as a common reference point for voltage and is used as a safety measure to provide a return path for current.

15. What is the difference between an insulator and a conductor? Answer: An insulator has high resistance and does not allow electric current to flow easily, while a conductor has low resistance and allows current to flow freely.

16. What is the purpose of a capacitor in a power supply circuit? Answer: Capacitors in a power supply circuit smooth out the rectified AC voltage and help in providing a more stable DC output.

17. What is the significance of the voltage regulation in a power system? Answer: Voltage regulation ensures that the voltage at the consumer end remains within specified limits, irrespective of load changes.

18. Explain the concept of apparent power, real power, and reactive power in AC circuits. Answer: Apparent power (S) is the vector sum of real power (P) and reactive power (Q), where P represents the actual power used in the circuit, and Q represents the power stored and returned by reactive elements like capacitors and inductors.

19. How does a photovoltaic cell work? Answer: A photovoltaic cell converts sunlight directly into electrical energy by the photovoltaic effect, where photons from sunlight excite electrons in a semiconductor material.

20. What is the purpose of a relay in an electrical circuit? Answer: A relay is an electromagnetic switch used to control high-power electrical devices by using a low-power control signal.

21. Define inductance. Answer: Inductance is the property of a circuit that opposes changes in current flow and is measured in henries (H).

22. What is the difference between an inverter and a converter? Answer: An inverter converts DC to AC, while a converter can refer to a device that changes the voltage level or converts AC to DC.

23. How do you calculate the power factor of a circuit? Answer: Power factor (PF) is the cosine of the angle between voltage and current in an AC circuit. It can be calculated as PF = Real Power (P) / Apparent Power (S).

24. What is the purpose of an oscilloscope? Answer: An oscilloscope is a test instrument used to visualize and analyze electronic signals in the time domain.

25. Differentiate between a resistor and a rheostat. Answer: A resistor is a fixed-value passive component, while a rheostat is a variable resistor used to adjust the flow of current in a circuit.

26. What is the difference between an NPN and a PNP transistor? Answer: NPN and PNP are two types of bipolar junction transistors (BJTs). In an NPN transistor, current flows from the collector to the emitter, while in a PNP transistor, current flows from the emitter to the collector.

27. Explain the working principle of a step-up transformer. Answer: A step-up transformer increases the voltage level while decreasing the current in the secondary winding compared to the primary winding.

28. What is the purpose of a capacitor in a filter circuit? Answer: Capacitors in a filter circuit allow AC signals to pass while blocking DC signals, helping to smooth out the output.

29. Define RMS value (Root Mean Square) of an AC voltage or current. Answer: RMS value is the equivalent steady DC value of an AC voltage or current and is used to represent the effective value of the AC waveform.

30. How do you calculate the total resistance of resistors connected in series? Answer: The total resistance (RT) of resistors connected in series can be calculated by summing up the individual resistances: RT = R1 + R2 + R3 + ...

31. What is the maximum power transfer theorem? Answer: The maximum power transfer theorem states that maximum power is transferred from a source to a load when the load resistance is equal to the source resistance.

32. Explain the difference between forward bias and reverse bias in a diode. Answer: Forward bias occurs when the positive terminal of the voltage source is connected to the P-type material and the negative terminal to the N-type material, allowing current flow. Reverse bias occurs when the positive terminal is connected to the N-type material and the negative terminal to the P-type material, blocking current flow.

33. What is the purpose of a snubber circuit? Answer: A snubber circuit is used to suppress voltage spikes or transients that may occur in power electronic devices.

34. What is the purpose of a zener diode? Answer: A zener diode is used as a voltage regulator to maintain a constant voltage across its terminals.

35. Differentiate between active and passive components. Answer: Active components can amplify or control electrical signals, while passive components do not have the ability to amplify signals and mainly control or manipulate the flow of current.

36. What is the function of an op-amp (operational amplifier)? Answer: Op-amps are widely used in analog electronic circuits to amplify signals, perform mathematical operations, and provide gain.

37. How does a synchronous motor differ from an induction motor? Answer: A synchronous motor operates at a constant speed and is synchronized with the frequency of the AC supply, while an induction motor operates at a speed slightly less than the synchronous speed and does not require synchronization.

38. Explain the concept of slip in an induction motor. Answer: Slip is the difference between the synchronous speed and the actual speed of the rotor in an induction motor.

39. What is a Schottky diode? Answer: A Schottky diode is a type of diode with a low forward voltage drop, making it ideal for high-speed switching applications.

40. Define the term "joule heating." Answer: Joule heating refers to the heat generated when electric current passes through a resistor due to the resistance encountered by the current flow.

41. What is the function of a choke in a lighting circuit? Answer: A choke (inductor) in a lighting circuit limits the current and prevents excessive current spikes.

42. Explain the principle of a half-wave rectifier. Answer: A half-wave rectifier converts only one-half of the AC input waveform into DC, using a diode to block the negative half.

43. What is the purpose of a flyback diode in a relay circuit? Answer: A flyback diode (freewheeling diode) is connected across the coil of a relay to protect other components from voltage spikes when the relay is turned off.

44. Differentiate between an AC motor and a DC motor. Answer: AC motors run on alternating current and do not require a commutator, while DC motors run on direct current and have a commutator.

45. What is a Schmitt trigger used for? Answer: A Schmitt trigger is a type of comparator used to convert an analog signal into a digital output, providing hysteresis and noise immunity.

46. Explain the working principle of a step-down transformer. Answer: A step-down transformer decreases the voltage level while increasing the current in the secondary winding compared to the primary winding.

47. What is the significance of power factor correction? Answer: Power factor correction is essential to minimize reactive power in the power system, reducing energy losses and improving the efficiency of power transmission.

48. What is the function of a capacitor in an AC circuit? Answer: Capacitors in an AC circuit are used to improve the power factor and provide reactive power compensation.

49. Differentiate between an ideal and a practical voltage source. Answer: An ideal voltage source provides a constant voltage regardless of the connected load, while a practical voltage source may have internal resistance and may drop its voltage with increasing load.

50. What is the difference between a synchronous generator and an asynchronous generator? Answer: A synchronous generator produces electricity at a constant speed, synchronized with the grid frequency, while an asynchronous generator can run at different speeds and does not require synchronization.

51. Explain the concept of hysteresis loss in a transformer. Answer: Hysteresis loss occurs in the transformer core due to the magnetic reversal of the core material as the alternating current flows through it, resulting in energy loss in the form of heat.

52. What is the purpose of a thermocouple in temperature measurement? Answer: A thermocouple is used to measure temperature by exploiting the principle that the voltage generated between two different metal conductors is proportional to the temperature difference.

53. Define the term "grounding" in electrical systems. Answer: Grounding is the process of connecting electrical equipment or circuits to the earth or a conductive body, providing a safe path for fault currents and protecting against electrical shocks.

54. What is the principle of a solar panel? Answer: Solar panels convert sunlight into electricity through the photovoltaic effect, where photons excite electrons in a semiconductor material.

55. Explain the working principle of a PN junction diode. Answer: A PN junction diode is formed by joining a P-type and an N-type semiconductor. It allows current to flow in one direction when forward-biased and blocks current flow when reverse-biased.

56. What is the difference between a primary cell and a secondary cell? Answer: A primary cell is non-rechargeable and cannot be recharged, while a secondary cell is rechargeable and can be reused multiple times.

57. What is the purpose of a load cell in electrical systems? Answer: A load cell is used to measure force or weight by converting mechanical force into an electrical signal.

58. How does a push-pull amplifier differ from a single-ended amplifier? Answer: A push-pull amplifier uses two transistors (or tubes) to amplify both halves of the AC waveform, while a single-ended amplifier amplifies only one half of the AC waveform.

59. Define the term "short circuit." Answer: A short circuit occurs when two points in an electrical circuit with different voltages are directly connected, resulting in excessive current flow.

60. What is the function of a varistor? Answer: A varistor is a voltage-dependent resistor used to protect electronic circuits from voltage spikes and transient overvoltages.

61. What is the difference between an isolator and a circuit breaker? Answer: An isolator is a switch used for isolating electrical equipment from the power source, while a circuit breaker is used to protect the circuit from overcurrent and short circuits.

62. Explain the working principle of a piezoelectric transducer. Answer: A piezoelectric transducer converts mechanical vibrations into electrical signals through the piezoelectric effect, where certain materials generate an electric charge when subjected to mechanical stress.

63. What is the purpose of a microcontroller in electronic devices? Answer: A microcontroller is a compact integrated circuit that contains a CPU, memory, and I/O peripherals, used for controlling and processing data in various electronic devices.

64. Differentiate between active and passive filters. Answer: Active filters use active components like op-amps to filter signals, while passive filters use only passive components like resistors, capacitors, and inductors.

65. What is the purpose of a current transformer (CT)? Answer: A current transformer is used to measure current in high-current power systems and steps down the current to a level suitable for measurement.

66. Explain the concept of steady-state and transient response in a power system. Answer: Steady-state refers to the system's behavior under normal operating conditions, while transient response describes the system's behavior during a sudden disturbance or fault.

67. What is the function of a gate in a power semiconductor device? Answer: A gate controls the switching behavior of a power semiconductor device, such as a MOSFET or IGBT, by turning it on or off.

68. What is the principle of a voltage multiplier circuit? Answer: A voltage multiplier circuit uses diodes and capacitors to increase the output voltage to a multiple of the input voltage.

69. Define the term "doping" in semiconductor materials. Answer: Doping is the process of intentionally adding impurities to semiconductor materials to modify their electrical properties, creating P-type or N-type regions.

70. What is the role of a step-up chopper in power electronics? Answer: A step-up chopper converts a lower DC voltage to a higher DC voltage using high-frequency switching.

71. Explain the working principle of a thermistor. Answer: A thermistor is a temperature-sensitive resistor whose resistance changes with temperature, providing an electrical signal proportional to the temperature.

72. Differentiate between an ideal and a practical inductor. Answer: An ideal inductor has no resistance and no magnetic losses, while a practical inductor has some resistance and magnetic losses due to the core material.

73. What is the function of a triac in electronic circuits? Answer: A triac is a bidirectional semiconductor device used for switching AC loads.

74. Explain the concept of motor torque. Answer: Motor torque is the rotational force generated by an electric motor, responsible for its ability to perform mechanical work.

75. What is the purpose of an ELCB (Earth Leakage Circuit Breaker)? Answer: An ELCB is a safety device used to detect and protect against electrical leakages to the earth, reducing the risk of electric shocks.

76. How does a supercapacitor differ from a regular capacitor? Answer: Supercapacitors, also known as ultracapacitors, have higher capacitance and energy storage capacity compared to regular capacitors.

77. What is the purpose of a snubber circuit in a power electronic device? Answer: A snubber circuit is used to reduce voltage spikes and electromagnetic interference in power electronic devices.

78. Differentiate between a step-up and a step-down chopper. Answer: A step-up chopper increases the output voltage compared to the input voltage, while a step-down chopper decreases the output voltage.

79. What is the role of a shunt resistor in a current measurement circuit? Answer: A shunt resistor is placed in series with the load to measure the current flowing through the circuit by measuring the voltage drop across it.

80. Explain the working principle of a full-wave rectifier. Answer: A full-wave rectifier converts both halves of the AC input waveform into DC using diodes, allowing current flow in the same direction for both positive and negative cycles.

81. What is the function of a pulse-width modulation (PWM) inverter? Answer: A PWM inverter generates a variable voltage by rapidly switching the DC input on and off, allowing the control of output voltage levels.

82. How does a fuse protect an electrical circuit? Answer: A fuse is designed to melt and break the circuit when excessive current flows through it, protecting the circuit and devices from damage due to overcurrent.

83. What is the significance of reactive power in a power system? Answer: Reactive power is essential for maintaining the voltage levels and supporting the operation of inductive loads, but it does not perform useful work.

84. Explain the working principle of a Hall effect sensor. Answer: A Hall effect sensor measures the magnetic field strength using the Hall effect, where a voltage is generated perpendicular to both the magnetic field and the current flow in a conductor.

85. What is the function of a transformer core? Answer: The transformer core provides a low-reluctance path for the magnetic flux generated by the primary winding, efficiently transferring energy to the secondary winding.

86. How does a variable frequency drive (VFD) control the speed of an AC motor? Answer: A VFD adjusts the frequency and voltage supplied to an AC motor, controlling its speed by altering the motor's magnetic field.

87. What is the purpose of an encoder in a motor control system? Answer: An encoder measures the rotation speed and position of a motor shaft, providing feedback to the control system for precise speed and position control.

88. What is the principle of a relay logic circuit? Answer: Relay logic uses electromechanical relays to perform logical functions in control systems.

89. Differentiate between an isolating transformer and a power transformer. Answer: An isolating transformer provides electrical isolation between input and output, while a power transformer is used for stepping up or stepping down voltage levels.

90. What is the purpose of a rectifier filter capacitor? Answer: The rectifier filter capacitor smooths out the pulsating DC output of a rectifier, providing a more stable DC voltage.

91. Explain the working principle of a gas discharge tube (GDT). Answer: A gas discharge tube is a voltage-triggered device that provides protection against voltage surges by conducting the excessive current to ground.

92. What is the difference between a unipolar and a bipolar stepper motor? Answer: A unipolar stepper motor has two windings per phase, while a bipolar stepper motor has one winding per phase.

93. Define the term "bandwidth" in the context of electronic circuits. Answer: Bandwidth is the range of frequencies over which an electronic circuit can effectively operate.

94. What is the purpose of a series resistor in an LED circuit? Answer: A series resistor is used to limit the current flowing through an LED to prevent damage.

95. Explain the concept of electric power transmission and distribution. Answer: Electric power transmission involves the long-distance transfer of high-voltage power from power plants to substations, while distribution involves lower voltage distribution to end consumers.

96. What is the role of a voltage regulator in a power supply circuit? Answer: A voltage regulator maintains a constant output voltage regardless of changes in input voltage or load.

97. Differentiate between an ammeter and a voltmeter. Answer: An ammeter measures current in a circuit, while a voltmeter measures voltage.

98. What is the function of a pulse transformer in electronic circuits? Answer: A pulse transformer is used to couple high-frequency signals between different stages of a circuit while providing electrical isolation.

99. Explain the concept of apparent power, real power, and reactive power in AC circuits. Answer: Apparent power is the product of the voltage and current amplitudes in an AC circuit. Real power is the actual power used to perform work, while reactive power is the power that oscillates between the source and the load.

100. What is the purpose of a surge protector in electrical systems? Answer: A surge protector (surge suppressor) is used to protect electronic devices from voltage spikes and transient overvoltages by diverting excessive current to ground.