1. What is the primary condition that must be satisfied for an oscillator circuit to sustain oscillations, in terms of voltage gain?
A. The voltage gain of the amplifier must be greater than or equal to 1, and the phase shift around the loop must be 360°
B. The voltage gain of the amplifier must be greater than 1
C. The voltage gain of the amplifier must be less than 1
D. The voltage gain of the amplifier must be equal to 1
Answer: A. The voltage gain of the amplifier must be greater than or equal to 1, and the phase shift around the loop must be 360°
Explanation:
For an oscillator to sustain continuous oscillations, it must satisfy the Barkhausen criterion, which states that the loop gain (product of amplifier gain and feedback factor) must be equal to or greater than 1, and the total phase shift around the loop must be 360° or 0°. This ensures that the signal reinforces itself constructively after each cycle, maintaining oscillation without external input.
A. \( J_{d} = \mu \frac{dH}{dt} \)
B. \( J_{d} = \nabla \times H \)
C. \( J_{d} = \sigma E \)
D. \( J_{d} = \epsilon \frac{dE}{dt} \)
The displacement current density is a concept introduced by Maxwell to extend Ampere’s law for time-varying electric fields. It is defined as \( J_{d} = \epsilon \frac{dE}{dt} \),
where \( \epsilon \) is the permittivity of the medium and \( E \) is the electric field.
In a second order control system, the peak overshoot depends on the damping ratio (\( \zeta \)).
As \( \zeta \) increases, the system becomes more damped, and the overshoot decreases.
The relationship is inversely proportional, given by:\( M_p = e^{\left(-\dfrac{\pi \zeta}{\sqrt{1 – \zeta^2}}\right)} \)
This shows that lower damping leads to higher overshoot, and vice versa.
Q.4 Determine the maximum voltage the capacitor can charge if the Series RC circuit is exited by a step function of amplitude ‘V’ volts.
A. V/2
B. V
C. 2V
D. 3V
Answer: B. V
Explanation:
In a Series RC circuit excited by a step input of amplitude ( V ), the capacitor charges gradually and asymptotically approaches the input voltage. The maximum voltage across the capacitor is equal to the step input voltage, i.e., V volts. This is because the capacitor blocks DC after full charge, and the voltage across it equals the applied DC voltage.
Q.5 If a transformer operates under no-load conditions, what will the primary current mainly consist of?
A. Secondary current
B. Load current
C. Magnetizing current
D. Copper loss current
Answer: C. Magnetizing current
Explanation:
Under no-load conditions, the transformer’s secondary is open, so no load current flows. However, the primary winding still draws a small current known as the magnetizing current, which is required to establish the magnetic flux in the core. This current is typically low and lags the voltage, representing the core excitation.
A. Entire z-plane
B. z < r
C. ROC does not exist.
D. z > r
For a right-sided sequence (x[n]), the Region of Convergence (ROC) of its Z-transform lies outside the outermost pole, i.e., |z| > r.
This ensures convergence of the infinite sum in the Z-transform definition:
X(z) = ∑n=0∞ x[n] z-n
The ROC is critical for stability and uniqueness of the transform.
Q.7 Which of the following is an application of an adder circuit?
A. Digital Comparator
B. Flip-Flop
C. Frequency Modulator
D. Arithmetic Logic Unit (ALU)
Answer: D. Arithmetic Logic Unit (ALU)
Explanation:
An adder circuit is a fundamental building block in digital electronics, used to perform binary addition. Its primary application is in the Arithmetic Logic Unit (ALU) of processors, where it enables operations like addition, subtraction, and logical functions. The ALU is central to computational tasks in digital systems.
Q.8 Voltage regulation in short transmission lines is usually very low because
A. the line length is short and the impedance is low
B. the series resistance is negligible
C. the series reactance is negligible
D. the power factor is usually high
Answer: A. the line length is short and the impedance is low
Explanation:
Voltage Regulation = (Vno-load – Vfull-load) / Vfull-load × 100%
Low impedance ensures minimal voltage variation between no-load and full-load.
A. The current at which the SCR turns off
B. The minimum anode current required to maintain conduction once triggered
C. The leakage current when SCR is off
D. The maximum gate current to trigger SCR
Answer: B. The minimum anode current required to maintain conduction once triggered
Explanation:
The latching current is the minimum anode current required to keep the SCR (Silicon Controlled Rectifier) in the ON state after the gate pulse is removed. If the current falls below this value immediately after triggering, the SCR will turn off. It ensures stable conduction post-triggering.
Q.10 The frequency of induced rotor current in a squirrel cage induction motor at full load is typically:
A. equal to the supply frequency
B. nearly zero
C. equal to the slip times supply frequency
D. equal to the stator frequency
Answer: C. equal to the slip times supply frequency
Explanation:
fr = s × fs
where s is the slip and fs is the supply frequency.
At full load, the slip is small (typically 2–5%), so the rotor current frequency is only a fraction of the supply frequency,
not equal to it.
Q.11 What is the transformation ratio of the teaser transformer in a Scott connection?
A. 0.5
B. 0.866
C. 0.707
D. 1.0
Answer: B. 0.866
Explanation:
In a Scott connection, the teaser transformer is connected at a point that is 86.6% of the main transformer winding, which corresponds to a transformation ratio of 0.866. This ensures balanced two-phase output from a three-phase supply.
Q.12 What effect does the positive temperature coefficient of channel resistance in MOSFETs have?
A. Reduces switching speed
B. Helps in automatic current sharing between parallel devices
C. Increases the conduction loss
D. Reduces gate-drive requirements
Answer: B. Helps in automatic current sharing between parallel devices
Explanation:
A positive temperature coefficient means that as temperature increases, the channel resistance increases. This property helps in automatic current sharing among parallel MOSFETs, preventing thermal runaway and ensuring safe operation.
Q.13 Voltage cancellation in current source inverters involves:
A. using zero-crossing detectors
B. connecting diodes in reverse bias
C. increasing input DC voltage
D. shifting the turn-on and turn-off times of switches
Answer: D. shifting the turn-on and turn-off times of switches
Explanation:
Voltage cancellation in current source inverters is achieved by adjusting the switching times of devices. By shifting turn-on and turn-off instants, the voltage spikes are minimized, improving output waveform quality.
Q.14 In the equivalent circuit of a transformer, what is the primary reason for considering leakage reactance?
A. It represents the resistance losses in the winding.
B. It shows the no-load current.
C. It represents the voltage drop due to the leakage flux.
D. It represents the voltage drop due to the leakage flux.
Answer: D. It represents the voltage drop due to the leakage flux.
Explanation:
Leakage reactance accounts for the voltage drop caused by flux that does not link both windings. It is essential in modeling real transformer behavior, especially under load conditions.
Q.15 The purpose of grading in underground cables is to .
A. reduce the cost of the cable
B. improve the voltage regulation
C. reduce the electric stress across the insulation
D. increase the current carrying capacity
Answer: C. reduce the electric stress across the insulation
Explanation:
Grading in cables involves using different dielectric materials or capacitive layers to distribute electric stress more evenly, thereby enhancing insulation life and preventing breakdown.
Q.16 The coordination of overcurrent relays in a protection system is designed to –
A. ensure that the relays operate at the same time during a fault
B. ensure that the relay closest to the fault operates first, isolating the fault without affecting the entire system
C. allow the most distant relay from the fault to operate first
D. guarantee that no relays operate during a fault
Answer: B. ensure that the relay closest to the fault operates first, isolating the fault without affecting the entire system
Explanation:
Relay coordination ensures selective tripping, where the nearest relay to the fault acts first. This minimizes disruption and protects healthy parts of the system.
Q.17 Which of the following correctly represents the Discrete-Time Fourier Transform (DTFT) of a discrete-time signal x[n]?
A. X(ω) = 8
B. X(ω) = ∫-∞∞ x[t] e-jωt dt
C. X(ω) = ∑n=-∞∞ x[n] ejωn
D. X(ω) = ∑n=-∞∞ x[n] e-jωn
X(ω) = ∑n=-∞∞ x[n] e-jωn,
which transforms the signal into the frequency domain.
Q.18 The transfer function H(s) of an LTI system is defined as:
A. Sum of input and output in Laplace domain
B. Ratio of output to input in time domain
C. Ratio of output to input in frequency domain
D. Ratio of input to output in time domain
Answer: C. Ratio of output to input in frequency domain
Explanation:
The transfer function ( H(s) ) is the Laplace domain ratio of output to input, i.e.,
( H(s) = \frac{Y(s)}{X(s)} ),
which characterizes the system’s frequency response.
Q.19 Select the correct option based on the given statements.
Statement 1: An independent voltage source maintains a constant voltage across its terminals regardless of the current drawn from it.
Statement 2: An independent current source maintains a constant current regardless of the voltage across its terminals.
A. Both Statement 1 and Statement 2 are incorrect.
B. Statement 1 is incorrect and Statement 2 is correct.
C. Statement 1 is correct and Statement 2 is incorrect.
D. Both Statement 1 and Statement 2 are correct.
Answer: D. Both Statement 1 and Statement 2 are correct
Explanation:
An independent voltage source maintains constant voltage, and an independent current source maintains constant current, regardless of load conditions. These are ideal source characteristics.
20. What is the typical voltage gain (magnitude) of a MOSFET common-source amplifier?
A. Greater than 1
B. Equal to 0
C. Less than 1
D. Equal to 1
Ans: A Greater than 1
Explanation:
The typical voltage gain of a MOSFET common-source amplifier is greater than 1 due to its ability to amplify the input signal effectively through its high transconductance.
Q.21 Consider the following statements and select the correct option.
Statement 1: When an RL circuit is connected in parallel with an RC circuit, the total current in the circuit will be the sum of the individual currents in both the branches.
Statement 2: The total impedance of the parallel combination of RL and RC circuits is always less than the impedance of the individual RL or RC circuits.
A. Both Statement 1 and Statement 2 are correct.
B. Both Statement 1 and Statement 2 are incorrect.
C. Statement 1 is incorrect, but Statement 2 is correct.
D. Statement 1 is correct, but Statement 2 is incorrect.
Answer: A. Both Statement 1 and Statement 2 are correct
Explanation:
Statement 1 is correct because, in a parallel circuit, the total current is the phasor sum of the individual branch currents, as per Kirchhoff’s Current Law.
Statement 2 is correct because the equivalent impedance of a parallel combination is always less than the smallest individual impedance, reducing the overall opposition to current flow.
Q.22 Which of the following statements about slip in an induction motor is correct?
A. Slip increases as the load on the motor increases.
B. Slip is always constant regardless of load.
C. Slip is always zero during no-load operation.
D. Slip is negative for motoring operation.
Answer: A. Slip increases as the load on the motor increases
Explanation:
In an induction motor, slip is the difference between synchronous speed and rotor speed. As the load increases, the rotor slows down, causing the slip to increase, which allows more current to be induced in the rotor and more torque to be generated.
Q.23 Select the correct option based on the given statements.
Statement 1: The resonance frequency of a series R-L-C circuit is dependent on the resistance (R), inductance (L) and capacitance (C).
Statement 2: At resonance, the impedance of a series R-L-C circuit is at its minimum value.
A. Statement 1 is incorrect and Statement 2 is correct.
B. Statement 1 is correct and Statement 2 is incorrect.
C. Both Statement 1 and Statement 2 are incorrect.
D. Both Statement 1 and Statement 2 are correct.
Answer: D. Both Statement 1 and Statement 2 are correct
Explanation:
Statement 1 is correct because while the resonance frequency is primarily determined by L and C (( \omega_0 = \frac{1}{\sqrt{LC}} )), the resistance R affects the quality factor and bandwidth, influencing the resonance behavior.
Statement 2 is correct because at resonance, the inductive and capacitive reactances cancel, leaving only the resistance, which is the minimum impedance.
Q.24 Select the correct option based on the given statements.
Statement 1: The reciprocity theorem states that in a linear network, the current in one branch due to a voltage source in another branch is the same as the current that would flow if the voltage source were in the second branch and the load were in the first branch.
Statement 2: The reciprocity theorem is only applicable for circuits with resistive elements.
A. Both Statement 1 and Statement 2 are false.
B. Statement 1 is true and Statement 2 is false.
C. Both Statement 1 and Statement 2 are true.
D. Statement 1 is false and Statement 2 is true.
Answer: B. Statement 1 is true and Statement 2 is false
Explanation:
Statement 1 is true because the Reciprocity Theorem applies to linear, bilateral networks, allowing the interchange of source and response locations.
Statement 2 is false because the theorem applies to circuits with resistors, capacitors, and inductors, not just resistive elements.
Q.25 A discrete-time LTI system is stable if the Region of Convergence (ROC) of its Z-transform:
A. exists anywhere in the z-plane
B. lies inside the unit circle
C. lies outside the unit circle
D. includes the unit circle
Answer: D. includes the unit circle
Explanation:
For a discrete-time LTI system to be BIBO stable, the ROC of its Z-transform must include the unit circle (( |z| = 1 )). This ensures that the system’s response to any bounded input remains bounded.
Q.26 In a voltage divider biasing circuit of a MOSFET, the voltage at the gate is determined by:
A. the threshold voltage of the MOSFET
B. the value of the source resistor
C. the ratio of the two resistors in the voltage divider network
D. the value of the drain resistor
Answer: C. the ratio of the two resistors in the voltage divider network
Explanation:
In voltage divider biasing, the gate voltage is set by the resistor ratio in the divider. The resistors form a potential divider from the supply voltage, establishing a fixed DC bias at the gate.
Q.27 What is the difference between a D flip-flop and a D latch?
A. There is no difference, both are same.
B. Flip-flop is edge-triggered, latch is level-triggered.
C. Flip-flop has no clock, latch has a clock.
D. Flip-flop is asynchronous, latch is synchronous.
Answer: B. Flip-flop is edge-triggered, latch is level-triggered
Explanation:
A D latch responds to the level of the clock signal, while a D flip-flop responds only to the edge (rising or falling). This makes flip-flops more suitable for synchronous systems.
Q.28 In an RL circuit, the impulse response represents the inductor’s reaction to a sudden voltage pulse. The current response of the RL circuit is ______________.
A. a step function
B. exponentially decreasing
C. a sine wave
D. exponentially increasing
Answer: A. a step function
Explanation:
An impulse voltage causes an instantaneous change in current in an RL circuit, resulting in a step function response. The inductor resists sudden changes in current, but the impulse forces a discontinuity.
Q.29 Identify the correct statement related to the ‘peak time’ parameter of a second order control system.
A. The peak time is the time taken for the system’s output to reach the first maximum value after a sinusoidal input is applied.
B. The peak time is the time taken for the system’s output to reach the fifth maximum (or peak) value after a sinusoidal input is applied.
C. The peak time is the time taken for the system’s output to reach the fifth maximum value after a step input is applied.
D. The peak time is the time taken for the system’s output to reach the first maximum value after a step input is applied.
Answer: D. The peak time is the time taken for the system’s output to reach the first maximum value after a step input is applied
Explanation:
Peak time is the time taken for the first peak in the system’s response to a step input. It reflects the speed of oscillation in underdamped systems.
Q.30 Identify the correct statement related to the ‘settling time’ parameter of a second order control system.
A. A lower natural frequency results in slower response, reducing the settling time.
B. A natural frequency cannot impact the settling time parameter.
C. A higher natural frequency results in a faster response, increasing the settling time.
D. A higher natural frequency results in a faster response, reducing the settling time.
Answer: D. A higher natural frequency results in a faster response, reducing the settling time
Explanation:
Settling time is the duration for the system to remain within a specified tolerance band around the final value. A higher natural frequency leads to quicker oscillations, thus reducing the settling time.
Q.31 A basic series inverter uses which of the following components to shape the output waveform?
A. Only inductors
B. RLC circuit
C. Only capacitors
D. Only resistors
Answer: B. RLC circuit
Explanation:
A basic series inverter employs an RLC circuit to shape the output waveform. The resonant behavior of the RLC network enables forced commutation of thyristors and helps produce a sinusoidal or quasi-sinusoidal output, filtering out harmonics effectively.
Q.32 How many inputs does a 2-bit comparator have?
A. 8
B. 2
C. 6
D. 4
Answer: D. 4
Explanation:
A 2-bit comparator compares two binary numbers, each with 2 bits: ( A = A_1A_0 ), ( B = B_1B_0 ). It requires 4 inputs—two bits from each number—to determine equality, greater than, or less than conditions.
Q.33 In a 3-phase transmission line, the self-inductance per unit length is given by the formula _______.
A. ( \frac{\mu}{2\pi} \ln \left( \frac{D_{eq}}{r’} \right) )
B. ( 2 \times 10^{-7} \ln \left( \frac{D_{eq}}{r’} \right) ) H/m
C. ( \frac{\mu_0}{2\pi} \ln \left( \frac{D_{eq}}{r’} \right) )
D. ( \frac{\mu}{8\pi} + \frac{\mu}{2\pi} \ln \left( \frac{1}{r} \right) )
Answer: A. ( \frac{\mu}{2\pi} \ln \left( \frac{D_{eq}}{r’} \right) )
Explanation:
This formula expresses the self-inductance per unit length of a conductor in a 3-phase transmission line, where ( \mu ) is the permeability, ( D_{eq} ) is the equivalent spacing, and ( r’ ) is the geometric mean radius (GMR) of the conductor.
Q.34 Which of the following is a characteristic of an ideal voltage source?
A. It maintains a constant current regardless of the voltage.
B. It has infinite internal resistance and can supply only a limited amount of current.
C. It has zero internal resistance and can supply any amount of current.
D. It has a finite internal resistance and can supply infinite current.
Answer: C. It has zero internal resistance and can supply any amount of current
Explanation:
An ideal voltage source maintains a constant voltage across its terminals, regardless of the load. It has zero internal resistance, allowing it to supply any required current without voltage drop.
Q.35 Which theorem states that any linear electrical network with voltage and current sources can be replaced by an equivalent circuit consisting of a single voltage source and a series resistance?
A. Thevenin’s Theorem
B. Norton’s Theorem
C. Superposition Theorem
D. Maximum Power Transfer Theorem
Answer: A. Thevenin’s Theorem
Explanation:
Thevenin’s Theorem simplifies a linear network to a single voltage source in series with a resistance, making analysis of load behavior easier. It’s especially useful for calculating current or voltage across a specific element.
Q.36 The standard for vector group classification in transformers is defined in:
A. IEC 60760
B. IS:2026 (Part IV)-1977
C. IS:2066 (Part III)-1980
D. IEEE Std 519
Answer: B. IS:2026 (Part IV)-1977
Explanation:
The vector group classification of transformers, which defines winding configurations and phase displacement, is specified in IS:2026 (Part IV)-1977, a key Indian Standard for transformer design and testing.
Q.37 A circuit breaker is used in electrical systems primarily for _______.
A. regulating the power flow in the circuit
B. protecting the system and disconnecting the load under abnormal conditions
C. reducing the voltage fluctuations
D. sensing the overcurrent
Answer: B. protecting the system and disconnecting the load under abnormal conditions
Explanation:
A circuit breaker protects electrical systems by interrupting current flow during faults such as overcurrent or short circuits, thereby preventing damage and ensuring safety.
Q.38 If the secondary voltage of a transformer remains constant, what happens when the load impedance decreases?
A. Core flux increases
B. Secondary current increases
C. Primary current decreases
D. Secondary current decreases
Answer: B. Secondary current increases
Explanation:
With a constant secondary voltage, a decrease in load impedance causes an increase in current as per Ohm’s Law. This higher secondary current also reflects as increased primary current due to transformer action.
Q.39 What is the primary limitation of using a log amplifier circuit with a diode in the feedback loop?
A. High offset voltage
B. Limited bandwidth
C. Non-linearity at high frequencies
D. Temperature dependence
Answer: D. Temperature dependence
Explanation:
A log amplifier using a diode in feedback relies on the exponential I-V characteristic, which is temperature-sensitive. Variations in temperature affect accuracy, making temperature dependence its main limitation.
Q.40 What device is connected in antiparallel to each thyristor in DC-AC inverter applications?
A. Resistor
B. Fuse
C. Capacitor
D. Diode
Answer: D. Diode
Explanation:
In DC-AC inverters, a diode is connected antiparallel to each thyristor to provide a path for inductive load current when the thyristor turns off. This ensures safe commutation and protects against reverse voltage stress.
Q.41 What is the output impedance of a Darlington pair?
A. Very high
B. Infinite
C. Zero
D. Very low
Answer: D. Very low
Explanation:
A Darlington pair consists of two BJTs connected such that the current amplified by the first is further amplified by the second. This configuration provides very high current gain and results in a very low output impedance, making it ideal for impedance buffering and high current drive applications.
Q.42 In a crystal oscillator circuit, what is the primary mechanism by which energy is transferred back to the crystal, causing it to oscillate?
A. Electromagnetic induction
B. Magnetic resonance
C. Electrostatic coupling
D. Piezoelectric effect
Answer: D. Piezoelectric effect
Explanation:
The piezoelectric effect allows crystals like quartz to convert electrical energy into mechanical vibrations and vice versa. In a crystal oscillator, this effect sustains oscillations by feeding energy back into the crystal, maintaining a stable and precise frequency.
Q.43 In a crystal oscillator circuit, what is the primary mechanism by which energy is transferred back to the crystal, causing it to oscillate?
A. Piezoelectric effect
B. Magnetic resonance
C. Electromagnetic induction
D. Electrostatic coupling
Answer: A. Piezoelectric effect
Explanation:
The piezoelectric effect is the core principle behind crystal oscillators. It enables reciprocal conversion between mechanical vibrations and electrical signals, allowing the crystal to sustain oscillations at its natural resonant frequency.
Q.44 In multilevel converters, the output voltage waveform is composed of:
A. discrete voltage levels
B. constant DC voltage
C. high-frequency triangular waves
D. pure sine waves
Answer: A. discrete voltage levels
Explanation:
Multilevel converters generate output waveforms using multiple discrete voltage levels, forming a staircase-like waveform. This approach reduces harmonic distortion and allows for better approximation of a sine wave with lower switching frequency.
Q.45 The Geometric Mean Distance (GMD) for calculating the self-inductance of a single-phase overhead transmission line refers to _______.
A. the average distance between the conductors
B. the square root of the product of distances between conductors
C. the mean of the distances between all pairs of conductors
D. the sum of the distances between conductors
Answer: B. the square root of the product of distances between conductors
Explanation:
GMD is used in inductance calculations and represents the square root of the product of distances between conductors. For a single-phase line, it simplifies to the distance between the two conductors, aiding in mutual inductance estimation.
Q.46 Which method is used for controlling the AC output voltage in a single-phase inverter?
A. Varying the gate pulse width
B. Varying the load impedance
C. Varying switching frequency
D. Using a step-down transformer
Answer: C. Varying switching frequency
Explanation:
In a single-phase inverter, varying the switching frequency can control the AC output voltage by influencing the average and RMS values of the waveform. Though PWM is more common, frequency variation is also used in specific control strategies.
Q.47 In sinusoidal PWM, what is the relationship between switching and output frequencies?
A. Output frequency is higher.
B. Both are equal.
C. Switching frequency is higher than output frequency.
D. Switching frequency is zero.
Answer: C. Switching frequency is higher than output frequency
Explanation:
In sinusoidal PWM, the switching frequency refers to the carrier frequency, which is much higher than the output (fundamental) frequency. This high switching rate enables fine control and low harmonic distortion in the output waveform.
Q.48 The linearity property of the Z-Transform states that:
A.
B.
C.
D.
Answer: C.
Explanation:
The linearity property of the Z-Transform states:
If ( x[n] \rightarrow X(z) ) and ( y[n] \rightarrow Y(z) ), then
( Z{a x[n] + b y[n]} = a X(z) + b Y(z) )
This allows superposition in system analysis, making it easier to handle linear combinations of signals.
Q.49 How does the inner cage of a double cage rotor contribute to the motor performance?
A. By increasing rotor reactance
B. By providing low resistance at running conditions
C. By reducing synchronous speed
D. By improving power factor at start
Answer: B. By providing low resistance at running conditions
Explanation:
In a double cage rotor, the inner cage has low resistance and high inductance, making it dominant during normal running conditions. This improves efficiency and speed regulation, while the outer cage aids in starting torque.
Q.50 What happens to the torque (T) if the supply voltage (V) is reduced to 50% in a squirrel cage induction motor?
A. Torque increases
B. Torque remains unchanged
C. Torque reduces to 25%
D. Torque reduces to 50%
Answer: C. Torque reduces to 25%
Explanation:
For a squirrel cage induction motor, the torque (T) is directly proportional to the square of the supply voltage (V), represented as ( T \propto V^2 ). If the supply voltage (V) is reduced to 50% (i.e., 0.5V), the new torque will be proportional to ( (0.5V)^2 = 0.25V^2 ). Consequently, the torque reduces to 25% of its original value.
Q.51 Which of the following statements correctly describes a property of the Discrete Fourier Transform (DFT) related to frequency-domain sampling and complex addition?
A. The DFT only works for signals with an even number of samples.
B. The DFT assumes that the time-domain signal is periodic and samples the frequency domain accordingly.
C. The DFT only provides real-valued outputs for any real-valued input signal.
D. The DFT can only be applied to continuous signals, not discrete signals.
Answer: B. The DFT assumes that the time-domain signal is periodic and samples the frequency domain accordingly.
Explanation:
The Discrete Fourier Transform (DFT) processes a finite-duration discrete-time signal. It inherently treats this finite sequence as one period of a periodically extended signal. As a result, the DFT computes the frequency spectrum by sampling the continuous-time Fourier transform in the frequency domain. This fundamental assumption means the time-domain signal is considered periodic, and the frequency domain is sampled in a corresponding manner.
Q.52 Which of the following equations represents the magnetic field intensity according to Biot-Savart’s Law?
A. ( H = \frac{1}{4\pi} \int \frac{I dl \times a_R}{R^2} )
B. ( H = \frac{1}{4\pi} \int \frac{I dl \cdot a_R}{R^2} )
C. ( H = \frac{1}{4\pi} \int \frac{I dl \times R}{R^3} )
D. ( H = \frac{1}{4\pi} \int \frac{I dl \cdot R}{R^3} )
Answer: C. ( H = \frac{1}{4\pi} \int \frac{I dl \times R}{R^3} )
Explanation:
Biot-Savart’s Law defines the magnetic field intensity (H) generated by a current-carrying element. The differential magnetic field intensity ( dH ) at a point due to a current element ( I dl ) is given by ( dH = \frac{I dl \times R}{4\pi R^3} ), where R is the position vector from the current element to the observation point. Integrating this expression over the entire current path yields the total magnetic field intensity.
Q.53 In a single-phase full-bridge voltage source inverter, what is the peak output voltage (fundamental component) for sinusoidal PWM with a modulation index ma = 1?
A. Vdc/2
B. Vdc
C. (4/π)⋅(Vdc/2)
D. (2/π)⋅Vdc
Answer: A. Vdc/2
Explanation:
For a single-phase full-bridge voltage source inverter employing sinusoidal Pulse Width Modulation (PWM), when the modulation index (ma) is equal to 1, the peak amplitude of the fundamental component of the output voltage is half of the DC link voltage (Vdc). This condition implies that the peak of the sinusoidal reference signal matches the peak of the triangular carrier signal, resulting in this specific output voltage relationship.
Q.54 In the unbalanced current test, what is typically used to apply reduced voltage to the winding?
A. A three-phase autotransformer
B. A rectifier circuit
C. A step-up transformer
D. A DC generator
Answer: A. A three-phase autotransformer
Explanation:
In an unbalanced current test, a three-phase autotransformer is typically used to apply reduced voltage to the winding. This setup allows for controlled testing conditions to evaluate parameters such as negative sequence impedance. Other options like rectifier circuits, step-up transformers, and DC generators do not serve the purpose of applying reduced AC voltage to an AC winding in this context.
Q.55 In the context of relays, selectivity refers to _______.
A. the accuracy of relay current settings
B. the ability of a relay to operate only for the intended fault condition
C. the speed at which the relay operates
D. the ability of a relay to trip without any delay
Answer: B. the ability of a relay to operate only for the intended fault condition
Explanation:
In power system protection, selectivity is a vital characteristic of protective relays. It describes the ability of a relay to precisely identify and isolate only the faulted section of a power system, while ensuring that the healthy sections remain operational. This minimizes service interruption by ensuring the relay operates only for the specific fault condition within its defined protection zone.
Q.56 Which of the following is a non-conventional source of power generation that uses the heat from the Earth’s internal sources?
A. Hydroelectric power
B. Geothermal power
C. Tidal power
D. Biomass power
Answer: B. Geothermal power
Explanation:
Geothermal power is categorized as a non-conventional source of power generation that harnesses heat originating from the Earth’s internal sources. This thermal energy, extracted from the Earth’s core and crust, is used to produce steam or hot water, which then drives turbines to generate electricity. Other options like hydroelectric, tidal, and biomass power are also renewable sources but do not primarily utilize the Earth’s internal heat.
Q.57 What is the borrow output of a half subtractor, when the inputs A = 0 and B = 1? Assume subtraction as A − B.
A. A
B. 1
C. B
D. 0
Answer: B. 1
Explanation:
In a half subtractor circuit, for inputs A and B, the difference (Diff) is ( A \oplus B ) (A XOR B), and the borrow output (( B_{out} )) is ( \bar{A}B ). Given the inputs A = 0 and B = 1, the subtraction is ( 0 – 1 ). To perform this operation, a borrow is necessary. Applying the borrow output formula, ( B_{out} = \bar{0} \cdot 1 = 1 \cdot 1 = 1 ). Thus, the borrow output is 1.
Q.58 Why do slip ring induction motors have better starting torque than squirrel cage motors?
A. They operate at a higher power factor.
B. They do not require external excitation.
C. They use laminated steel rotors.
D. They have external resistance in the rotor circuit.
Answer: D. They have external resistance in the rotor circuit.
Explanation:
Slip ring induction motors achieve better starting torque compared to squirrel cage motors primarily because they allow for the insertion of external resistance into the rotor circuit. By increasing the rotor resistance during startup, both the rotor current and the power factor at start are significantly improved, leading to a higher starting torque. This external resistance can then be progressively reduced as the motor accelerates to its operating speed.
Q.59 The power loss in a short transmission line is primarily due to _______.
A. the series resistance
B. the series reactance
C. the shunt capacitance
D. the series inductance
Answer: A. the series resistance
Explanation:
In a short transmission line, the primary components considered for analysis are its series resistance (R) and series inductance (L) (which contributes to series reactance ( X_L )). However, power loss in any electrical circuit is predominantly caused by the resistance, manifested as ( I^2R ) losses (also known as copper losses). While reactance influences voltage drops and reactive power flow, it does not directly dissipate active power. Therefore, for a short transmission line, the series resistance is the dominant factor responsible for power loss. Shunt capacitance is typically negligible in these lines.
Q.60 What is Electric Field Density for a point charge Q located at origin, as per Gauss’s Law?
A. ( \vec{D} = \frac{Q}{4\pi r^2} \vec{a_\phi} )
B. ( \vec{D} = \frac{Q}{4\pi r^2} \vec{a_r} )
C. ( \vec{D} = \frac{Q}{4\pi r} \vec{a_r} )
D. ( \vec{D} = \frac{Q}{4\pi r^3} \vec{a_r} )
Answer: B. ( \vec{D} = \frac{Q}{4\pi r^2} \vec{a_r} )
Explanation:
According to Gauss’s Law, for a point charge Q situated at the origin in free space, the electric flux density (( \vec{D} )) can be determined by considering a spherical Gaussian surface of radius ( r ) enclosing the charge. The total electric flux through this surface is equal to the enclosed charge Q. Since the electric field density is directed radially outward and is uniform over the spherical surface, the magnitude of ( \vec{D} ) is ( \frac{Q}{4\pi r^2} ). In its vector form, with ( \vec{a_r} ) representing the unit radial vector, the Electric Field Density is ( \vec{D} = \frac{Q}{4\pi r^2} \vec{a_r} ).
Q.61 What is the Region of Convergence (ROC) for a finite-duration discrete-time signal x[n]?
A. The ROC is an annulus.
B. The ROC lies outside a circle.
C. The ROC lies inside a circle.
D. The ROC is the entire z-plane, possibly excluding z=0 or z=infinity.
Answer: D. The ROC is the entire z-plane, possibly excluding z=0 or z=infinity
Explanation:
For a finite-duration discrete-time signal x[n], the Region of Convergence (ROC) for its Z-transform is the entire z-plane. This means the transform converges for all values of z, except possibly at z = 0 or z = ∞, depending on whether the signal includes terms for n > 0 or n < 0. Therefore, the ROC is the entire z-plane, with possible exclusions at the extremes.
Q.62 If there is no surface current (Js = 0) at the interface between two media, what happens to the tangential component of the magnetic field intensity (H) across the boundary?
A. The tangential component of H remains continuous.
B. The tangential component of H becomes zero.
C. The tangential component of H is always discontinuous.
D. The normal component of H is always equal to Js.
Answer: A. The tangential component of H remains continuous
Explanation:
According to electromagnetic boundary conditions, when there is no surface current (Js = 0) at the interface between two media, the tangential component of the magnetic field intensity (H) remains continuous across the boundary. This means the value of H tangential to the surface is equal on both sides of the interface.
Q.63 In a buck converter operating in continuous-conduction mode, what happens when the switch is ON?
A. Diode conducts
B. Inductor charges and current increases linearly
C. Output voltage drops to zero
D. Inductor current stops
Answer: B. Inductor charges and current increases linearly
Explanation:
In a buck converter operating in continuous-conduction mode, when the switch is ON, the input voltage is applied across the inductor. This causes the inductor to store energy, and the current through the inductor increases linearly. During this time, the diode is reverse-biased and does not conduct.
Q.64 The convolution property of the Z-Transform states that:
A. ( Z{ax[n] + by[n]} = aX(z) + bY(z) )
B. ( Z{x[n-k]} = z^{-k}X(z) )
C. ( Z{x[n] * h[n]} = X(z)H(z) )
D. ( Z{x[n]} = \sum_{n=-\infty}^{\infty} x[n]z^{-n} )
Answer: C. ( Z{x[n] * h[n]} = X(z)H(z) )
Explanation:
The convolution property of the Z-Transform states that the Z-transform of the convolution of two discrete-time signals ( x[n] ) and ( h[n] ) is equal to the product of their individual Z-transforms. That is, if ( y[n] = x[n] * h[n] ), then ( Y(z) = X(z)H(z) ). This property is essential for analyzing linear time-invariant (LTI) systems.
Q.65 Identify whether the following statements are true or false.
Statement 1: The Superposition Theorem is used in AC circuits to simplify the analysis when there are multiple independent sources (voltage or current). The theorem states that the response in a linear circuit with multiple sources is the sum of the responses from each individual source acting alone.
Statement 2: The Superposition Theorem is only applicable to DC circuits.
A. Statement 1 is false, and Statement 2 is true.
B. Both Statement 1 and Statement 2 are true.
C. Statement 1 is true, but Statement 2 is false
D. Both Statement 1 and Statement 2 are false.
Answer: C. Statement 1 is true, but Statement 2 is false
Explanation:
Statement 1 is true because the Superposition Theorem applies to linear circuits with multiple independent sources, whether AC or DC, and allows the total response to be calculated as the sum of individual responses.
Statement 2 is false because the theorem is not limited to DC circuits; it is valid for AC circuits as well.
Q.66 If the time constant of the RC series circuit is 1 sec and the value of capacitor C = 1µF, determine the value of resistor R.
A. 10 KΩ
B. 10 MΩ
C. 100 KΩ
D. 1 MΩ
Answer: D. 1 MΩ
Explanation:
The time constant (τ) of an RC circuit is given by ( \tau = RC ).
Given: ( \tau = 1 ) sec, ( C = 1 \mu F = 1 \times 10^{-6} F )
Then, ( R = \frac{\tau}{C} = \frac{1}{1 \times 10^{-6}} = 1 \times 10^6 \Omega = \mathbf{1 M\Omega} )
Q.67 Determine the Neper frequency (in rad/s) of a series RLC circuit if R = 1 MΩ, C = 1 µF, and L = 1 mH.
A. 0.5
B. 1
C. 1.5
D. 2
Answer: A. 0.5
Explanation:
The Neper frequency (α), also called the damping coefficient, is given by ( \alpha = \frac{R}{2L} ).
Given: ( R = 1 M\Omega = 1 \times 10^6 \Omega ), ( L = 1 mH = 1 \times 10^{-3} H )
Then, ( \alpha = \frac{1 \times 10^6}{2 \times 1 \times 10^{-3}} = 0.5 \times 10^9 ) rad/s
This result is extremely large, indicating a possible unit mismatch or unrealistic component values. However, assuming the question intends a simplified interpretation, the answer marked is 0.5, possibly based on different assumed values.
Q.68 Which of the following applications is NOT suitable for a squirrel cage induction motor?
A. Conveyors in factories
B. Air compressors
C. CNC machines requiring precise speed control
D. Centrifugal pumps
Answer: C. CNC machines requiring precise speed control
Explanation:
Squirrel cage induction motors are ideal for applications with constant or near-constant speed, such as conveyors, compressors, and pumps. However, they are not suitable for applications requiring precise speed control, like CNC machines, which require fine adjustments and feedback mechanisms. Such tasks are better handled by DC motors or AC motors with variable frequency drives (VFDs).
Q.69 What is the key difference between a JK and a T flip-flop in terms of conversion?
A. JK has an undefined state.
B. T cannot be implemented using JK.
C. JK has 2 inputs, while T has 1.
D. T is asynchronous, while JK is synchronous.
Answer: C. JK has 2 inputs, while T has 1
Explanation:
A JK flip-flop has two inputs (J and K), allowing for set, reset, hold, and toggle operations. A T flip-flop has one input (T) and toggles its state when T is high and a clock pulse is applied. A T flip-flop can be implemented using a JK flip-flop by connecting J and K together.
Q.70 Which of the following options represents a Poisson’s equation in electrostatics for a charge-free region?
A. ( \nabla^2 V = 0 )
B. ( \nabla \cdot \vec{D} = \rho_v )
C. ( \vec{E} = -\nabla V )
D. ( \nabla \times \vec{E} = -\frac{\partial \vec{B}}{\partial t} )
Answer: A. ( \nabla^2 V = 0 )
Explanation:
Poisson’s equation relates the electric potential (V) to the volume charge density (( \rho_v )) as ( \nabla^2 V = -\frac{\rho_v}{\epsilon} ). In a charge-free region, ( \rho_v = 0 ), so the equation simplifies to ( \nabla^2 V = 0 ), which is known as Laplace’s equation. This form is used to describe electrostatic potential in regions without free charge.
Q.71 Identify the correct statement with respect to unit step response of a second order system.
A. The settling time is always zero
B. The settling time is greater than the rise time
C. The settling time is equal to the rise time
D. The settling time is less than the rise time
Answer: B. The settling time is greater than the rise time
Explanation:
In a second-order system, the rise time is the duration taken for the response to move from a lower percentage (e.g., 10%) to a higher percentage (e.g., 90%) of its final value. The settling time is the time required for the response to remain within a specified tolerance band (e.g., ±2%) around the final value. Due to oscillations and damping, the system takes longer to settle than to rise, making the settling time greater than the rise time.
Q.72 Which mode of dual converter operation involves only one bridge conducting at a time?
A. Circulating current-free operation
B. Simultaneous conduction mode
C. Freewheeling operation
D. Circulating current mode
Answer: A. Circulating current-free operation
Explanation:
In a dual converter, two bridges are used to control current direction. In circulating current-free operation, only one bridge conducts at a time, preventing circulating currents between the converters. This mode simplifies control and reduces power losses, making it suitable for applications where bidirectional current control is needed without simultaneous conduction.
Q.73 The impulse response of a second order system can be obtained by:
A. differentiating the step response of the second order system
B. first integrating and then differentiating the step response of the second order system
C. giving a ramp function at the input and then differentiating the step response of the second order system
D. integrating the step response of the second order system
Answer: A. differentiating the step response of the second order system
Explanation:
In linear time-invariant (LTI) systems, the impulse response is the derivative of the step response. Since the unit impulse is the derivative of the unit step function, the system’s response to an impulse input can be obtained by differentiating its step response. This method applies to second-order systems and helps in analyzing system dynamics.
Q.74 Which of the following statements is correct regarding the inductance of a toroidal coil with a high-permeability core?
A. The inductance is inversely proportional to the square of the number of turns.
B. The inductance increases as the number of turns increases.
C. The inductance is independent of the core material.
D. The inductance decreases as the permeability of the core increases.
Answer: B. The inductance increases as the number of turns increases
Explanation:
The inductance (L) of a toroidal coil is given by ( L = \frac{\mu N^2 A}{l} ), where ( \mu ) is the permeability, N is the number of turns, A is the cross-sectional area, and l is the mean length of the magnetic path. Since L is proportional to ( N^2 ), increasing the number of turns increases the inductance, enhancing the coil’s ability to store magnetic energy.
Q.75 The Rate of Rise of Recovery Voltage (RRRV) is an important parameter in switchgear protection because it _______.
A. determines the fault current in the system
B. indicates the speed at which the voltage returns to normal after a fault is cleared
C. defines the speed at which a circuit breaker opens
D. measures the efficiency of the protection system
Answer: C. defines the speed at which a circuit breaker opens
Explanation:
The Rate of Rise of Recovery Voltage (RRRV) refers to how quickly the voltage across circuit breaker contacts increases after current interruption. A high RRRV imposes electrical stress on the breaker, requiring it to open rapidly to avoid re-ignition of the arc. Thus, RRRV influences the design and speed of circuit breaker operation, ensuring safe and reliable fault clearance.
Q.76 What happens to the output voltage when the pulse width increases in PWM control?
A. Output becomes distorted.
B. Output voltage decreases.
C. Output frequency increases.
D. Output voltage increases.
Answer: D. Output voltage increases
Explanation:
In Pulse Width Modulation (PWM) control, the average output voltage is directly proportional to the pulse width (or duty cycle). When the pulse width increases, the switch remains ON for a longer duration during each cycle, resulting in a higher average output voltage.
Q.77 What is the primary limitation of using a differentiator circuit with an OPAMP in a practical application?
A. Limited bandwidth
B. Inability to handle high-input impedance sources
C. Difficulty in achieving stable operation
D. High noise sensitivity
Answer: D. High noise sensitivity
Explanation:
An OPAMP-based differentiator circuit amplifies the rate of change of input signals, which makes it highly sensitive to high-frequency noise. Since noise typically contains high-frequency components, the differentiator tends to amplify unwanted signals, leading to a noisy and unstable output in practical applications.
Q.78 Identify the correct statement related to transient response characteristics of a second order control system.
A. The delay time is directly proportional to the damped natural frequency.
B. The delay time is independent of the damped natural frequency.
C. The delay time is inversely proportional to the damped natural frequency.
D. The delay time is always a constant and does not dependent on any system parameter
Answer: C. The delay time is inversely proportional to the damped natural frequency
Explanation:
In a second-order control system, the delay time indicates how quickly the system begins to respond. It is inversely proportional to the damped natural frequency (( \omega_d )), meaning that higher ( \omega_d ) leads to faster response and shorter delay time.
Q.79 If the damping ratio for a second order system in a control system is represented by ‘d’ (its Zeta generally), then we get Underdamped Response if ________________ and overdamped Response if ___________.
A. 0 < d < 1; d > 1
B. d = 1; d = 0
C. d = 0; d = 1
D. d > 1; d < 1
Answer: A. 0 < d < 1; d > 1
Explanation:
The damping ratio (d or ( \zeta )) determines the nature of the system’s response:
- Underdamped response occurs when ( 0 < d < 1 ), resulting in oscillations.
- Overdamped response occurs when ( d > 1 ), leading to a slow, non-oscillatory return to steady state.
Q.80 What is the magnetic field intensity due to straight current carrying filamentary conductor of infinite length? (where conductor is along the z-axis)
A. ( \vec{H} = \frac{I}{2\pi \rho} \vec{a_\phi} )
B. ( \vec{H} = \frac{I}{2\pi \rho} \vec{a_z} )
C. ( \vec{H} = \frac{I}{4\pi \rho} \vec{a_\phi} )
D. ( \vec{H} = \frac{I}{4\pi \rho} \vec{a_z} )
Answer: A. ( \vec{H} = \frac{I}{2\pi \rho} \vec{a_\phi} )
Explanation:
Using Ampere’s Law, the magnetic field intensity (( \vec{H} )) around an infinitely long straight conductor is given by ( \vec{H} = \frac{I}{2\pi \rho} \vec{a_\phi} ), where ( \rho ) is the radial distance and ( \vec{a_\phi} ) is the azimuthal unit vector, indicating that the field forms concentric circles around the conductor.
Q.81 Why are single squirrel cage induction motors preferred in irrigation pump sets?
A. They operate with DC supply.
B. They have high starting torque.
C. They offer variable speed control.
D. They provide fairly constant speed and high efficiency.
Answer: D. They provide fairly constant speed and high efficiency
Explanation:
Squirrel cage induction motors are ideal for irrigation pump sets due to their constant speed, high efficiency, and robust construction. These features ensure reliable and economical operation under varying load conditions, making them suitable for agricultural applications.
Q.82 What does the control parameter α represent in the overlapping control of the chopper?
A. Firing angle
B. Power factor
C. Duty cycle
D. Resistance setting of RB
Answer: C. Duty cycle
Explanation:
In chopper circuits, the control parameter ( \alpha ) represents the duty cycle, which is the ratio of ON-time to total switching period. By adjusting ( \alpha ), the average output voltage of the chopper can be precisely controlled.
Q.83 What is the Z-transform of x[n + k] in terms of X(z)?
A. ( z^k X(z) – \sum_{i=0}^{k-1} x[i]z^{k-i} )
B. ( z^k X(z) )
C. ( z^{-k} X(z) )
D. ( z^k X(z) + \sum_{i=0}^{k-1} x[i]z^{k-i} )
Answer: D. ( z^k X(z) + \sum_{i=0}^{k-1} x[i]z^{k-i} )
Explanation:
The Z-transform of ( x[n + k] ) involves a forward shift and includes initial condition terms. The expression ( z^k X(z) + \sum_{i=0}^{k-1} x[i]z^{k-i} ) accounts for both the shifted transform and the additional terms introduced by the shift.
Q.84 What type of shift register allows data to be shifted in both left and right directions?
A. Serial-in parallel-out (SIPO)
B. Serial-in serial-out (SISO)
C. Parallel-in serial-out (PISO)
D. Universal shift register
Answer: D. Universal shift register
Explanation:
A universal shift register supports bidirectional shifting, parallel loading, and serial input/output. Its versatility makes it suitable for complex data manipulation tasks in digital systems.
Q.85 In differential protection, the basic principle is based on the comparison of _______.
A. voltage at the two ends of the line
B. resistance at the two ends of the line
C. power factor of supply and load
D. current entering and leaving a protected zone
Answer: D. current entering and leaving a protected zone
Explanation:
Differential protection compares the current entering and leaving a protected zone. Under normal conditions, these currents are equal. A difference indicates a fault, triggering the protective relay to isolate the faulted section.
Q.86 Which of the following options is correct regarding the magnetic vector potential (A) and the magnetic field intensity (B)?
A. B is the curl of A.
B. B is the gradient of A.
C. B is the Laplacian of A.
D. B is the divergence of A.
Answer: A. B is the curl of A
Explanation:
In electromagnetics, the magnetic field intensity (( \vec{B} )) is defined as the curl of the magnetic vector potential (( \vec{A} )), expressed as ( \vec{B} = \nabla \times \vec{A} ). This relationship is fundamental in Maxwell’s equations.
Q.87 If the transfer function of the control system has 4 poles and 2 zeros, then the order of the system is:
A. 4
B. 6
C. 2
D. 8
Answer: A. 4
Explanation:
The order of a control system is determined by the number of poles, which corresponds to the highest power of ‘s’ in the denominator of the transfer function. Therefore, with 4 poles, the system is of order 4, regardless of the number of zeros.
Q.88 In a basic current mirror circuit using two identical bipolar junction transistors (BJTs), the collector current of the output transistor (Q2) is:
A. equal to the collector current of the input transistor (Q1)
B. twice the collector current of the input transistor (Q1)
C. equal to the base current of the input transistor (Q1)
D. half the collector current of the input transistor (Q1)
Answer: A. equal to the collector current of the input transistor (Q1)
Explanation:
A current mirror circuit uses matched BJTs to replicate a reference current. When Q1 and Q2 are identical and base currents are negligible, the collector current of Q2 mirrors that of Q1. This ensures a stable and equal output current, making the circuit useful for biasing and current control.
Q.89 Select the correct option based on the given statements.
Statement 1: In a parallel circuit, the voltage across each component is the same as the source voltage.
Statement 2: The total current in a parallel circuit is equal to the sum of the currents through all the branches.
A. Statement 1 is incorrect and Statement 2 is correct.
B. Both Statement 1 and Statement 2 are correct.
C. Both Statement 1 and Statement 2 are incorrect.
D. Statement 1 is correct and Statement 2 is incorrect.
Answer: B. Both Statement 1 and Statement 2 are correct
Explanation:
In a parallel circuit, each branch is connected directly across the source, so the voltage across each component is the same. According to Kirchhoff’s Current Law (KCL), the total current entering the parallel network is equal to the sum of the branch currents. Thus, both statements are correct.
Q.90 What is the major difference between a T flip-flop and a JK flip-flop?
A. T flip-flop toggles on every clock pulse when T = 1, while JK flip-flop follows J and K inputs.
B. T flip-flop has two inputs, whereas JK flip-flop has one input.
C. JK flip-flop does not require a clock.
D. T flip-flop cannot be used in counters.
Answer: A. T flip-flop toggles on every clock pulse when T = 1, while JK flip-flop follows J and K inputs
Explanation:
A T flip-flop has a single input (T) and toggles its output on each clock pulse when T = 1. A JK flip-flop has two inputs (J and K) and can set, reset, hold, or toggle based on their values. The T flip-flop is a simplified version of the JK flip-flop, often implemented by connecting J and K together.
Q.91 The Region of Convergence (ROC) of a left-sided sequence in the Z-domain is:
A. at ( |z| = 1 )
B. inside the circle ( |z| < r )
C. at no specific region
D. outside the circle ( |z| > r )
Answer: B. inside the circle ( |z| < r )
Explanation:
For a left-sided sequence ( x[n] ), where ( x[n] = 0 ) for ( n > N_0 ), the Region of Convergence (ROC) in the Z-domain is typically inside a circle, defined by ( |z| < r ), where r is related to the pole furthest from the origin. This ROC may exclude ( z = 0 ) if the sequence extends to negative infinity.
Q.92 In an AC circuit, improving the power factor can be achieved by:
A. reducing the supply voltage
B. adding inductors in parallel
C. increasing the circuit resistance
D. adding capacitors in parallel
Answer: D. adding capacitors in parallel
Explanation:
To improve power factor in an AC circuit, especially with inductive loads, the most effective method is to add capacitors in parallel. Capacitors provide leading reactive power, which cancels out the lagging reactive power from inductors, thereby raising the power factor. Reducing supply voltage does not directly improve power factor.
Q.93 Which of the following modifications can be made to a 4-bit parallel adder to perform subtraction?
A. Complement one of the inputs and add 1.
B. Use XOR gates to invert the carry.
C. Increase the number of adders.
D. Connect the output carry to input carry.
Answer: A. Complement one of the inputs and add 1
Explanation:
To perform subtraction using a 4-bit parallel adder, the two’s complement method is used. This involves complementing the subtrahend (one’s complement) and adding 1 to the result. The operation ( A – B ) becomes ( A + (\text{two’s complement of } B) ), enabling subtraction using addition logic.
Q.94 What happens when J = 0 and K = 1 in a JK flip-flop?
A. The output resets to 0.
B. The output remains the same.
C. The output sets to 1.
D. The output toggles.
Answer: A. The output resets to 0
Explanation:
In a JK flip-flop, when J = 0 and K = 1, the flip-flop enters the reset state. On the active clock edge, the output Q becomes 0. The condition for the output to remain unchanged is when both J and K are 0.
Q.95 In a control system, if the input is a unit step function, then the steady state error for type-1 system is _____ and for type-2 system is _____.
A. zero; infinity
B. unity; infinity
C. zero; unity
D. zero; zero
Answer: D. zero; zero
Explanation:
For a unit step input, the steady-state error depends on the system type:
- A Type-1 system has one pole at origin, yielding infinite position error constant ( K_p ) and zero steady-state error.
- A Type-2 system has two poles at origin, also resulting in zero steady-state error for step input.
Q.96 Which of the following statements correctly describes the force experienced by a charged particle moving in a magnetic field?
A. The force is in the opposite direction of the magnetic field.
B. The force is perpendicular to both the velocity of the particle and the magnetic field.
C. The force is zero regardless of the particle’s motion.
D. The force is in the direction of the particle’s velocity.
Answer: B. The force is perpendicular to both the velocity of the particle and the magnetic field
Explanation:
The Lorentz force law states ( \vec{F} = q(\vec{v} \times \vec{B}) ), where ( \vec{F} ) is the force, ( \vec{v} ) is the velocity, and ( \vec{B} ) is the magnetic field. The cross product ensures that the force is perpendicular to both vectors, resulting in circular or helical motion of the particle.
Q.97 In distance protection, the relay operates when _______.
A. the current exceeds a set value
B. the load current exceeds the rated value
C. the voltage exceeds a set value
D. the impedance between the relay and the faulted section falls below a set value
Answer: D. the impedance between the relay and the faulted section falls below a set value
Explanation:
Distance protection relays measure the impedance between their location and the fault. If the measured impedance drops below a preset threshold, it indicates a fault within the protected zone, prompting the relay to trip and isolate the fault.
Q.98 The time-delay characteristic of overvoltage protection is used to _______.
A. ensure that the protection operates only after a full fault occurs
B. allow for brief voltage surges to pass without causing a trip
C. delay relay operation during transient faults
D. prevent tripping during minor overloads
Answer: B. allow for brief voltage surges to pass without causing a trip
Explanation:
Time-delay characteristics in overvoltage protection prevent nuisance tripping due to short-duration surges. This ensures that only sustained overvoltage conditions trigger the protection, maintaining system stability and avoiding unnecessary interruptions.
Q.99 In the steady-state response of an RL circuit, the voltage across the inductor is _____________.
A. half of the supply voltage
B. zero
C. equal to the supply voltage
D. proportional to the current
Answer: B. zero
Explanation:
In steady-state DC conditions, the current in an RL circuit becomes constant, so ( \frac{di}{dt} = 0 ). Since the inductor voltage is ( V_L = L \frac{di}{dt} ), it becomes zero, and the inductor behaves like a short circuit.
Q.100 What is the main advantage of an auto transformer over a two-winding transformer?
A. Can work with DC supply
B. Has higher efficiency and smaller size
C. Completely eliminates core losses
D. Has separate primary and secondary windings
Answer: B. Has higher efficiency and smaller size
Explanation:
An autotransformer uses a single winding for both primary and secondary, reducing material usage and copper losses. This leads to higher efficiency and a more compact design compared to a two-winding transformer, making it ideal for voltage regulation and power distribution.
Q.101 What is the primary mechanism by which a voltage-controlled oscillator (VCO) achieves frequency modulation in response to a control voltage?
A. Varactor diode capacitance variation
B. Bipolar junction transistor (BJT) base-emitter voltage variation
C. Junction field-effect transistor (JFET) transconductance variation
D. Resistor-capacitor (RC) time constant variation
Answer: A. Varactor diode capacitance variation
Explanation:
A voltage-controlled oscillator (VCO) achieves frequency modulation by using a varactor diode, whose capacitance varies with reverse-bias voltage. This diode is placed in the resonant tank circuit, and changes in control voltage alter the capacitance, thereby shifting the resonant frequency and modulating the output.
Q.102 A capacitor is connected across a 5 V DC voltage source at time seconds through a switch. The current at seconds will be _______.
A. 1 A
B. 0.5 A
C. 0 A
D. 2.5 A
Answer: C. 0 A
Explanation:
In a DC circuit, once a capacitor is fully charged, it behaves like an open circuit. At steady state, the current through the capacitor is zero, since ( \frac{dV}{dt} = 0 ). Therefore, the current at time seconds (after charging) is 0 A.
Q.103 What happens to the rotor resistance of a deep bar rotor as the motor speed increases?
A. It increases
B. It decreases
C. It fluctuates randomly
D. It remains constant
Answer: B. It decreases
Explanation:
In a deep bar rotor, the skin effect causes current to flow in the outer layers at low speed, increasing effective resistance. As motor speed increases, the rotor frequency decreases, reducing the skin effect and allowing current to penetrate deeper, thus decreasing the rotor resistance.
Q.104 While calculating the final value theorem for a function F(s) and f(t), the limit is applied as:
A. ( t \to 0 ) for ( f(t) ) and ( s \to \infty ) for ( F(s) )
B. ( t \to \infty ) for ( f(t) ) and ( s \to \infty ) for ( F(s) )
C. ( t \to \infty ) for ( f(t) ) and ( s \to 0 ) for ( F(s) )
D. ( t \to 0 ) for ( f(t) ) and ( s \to 0 ) for ( F(s) )
Answer: C. ( t \to \infty ) for ( f(t) ) and ( s \to 0 ) for ( F(s) )
Explanation:
The Final Value Theorem states:
( \lim_{t \to \infty} f(t) = \lim_{s \to 0} sF(s) )
This allows determination of the steady-state value of a time-domain function using its Laplace transform.
Q.105 For long transmission lines, the voltage regulation becomes worse when _______.
A. the length of the transmission line decreases
B. the current is reduced
C. the line is lightly loaded
D. the line is heavily loaded
Answer: C. the line is lightly loaded
Explanation:
In long transmission lines, under light load or no-load conditions, the Ferranti effect causes the receiving-end voltage to exceed the sending-end voltage due to line capacitance. This results in poor voltage regulation, especially when the line is lightly loaded.
Q.106 In forced commutation, which parameter is forced to zero to turn off the SCR?
A. Anode-to-cathode voltage
B. Anode current
C. Gate voltage
D. Holding voltage
Answer: B. Anode current
Explanation:
An SCR remains ON as long as the anode current exceeds the holding current. In forced commutation, the anode current is actively reduced below the holding level, turning the SCR OFF, regardless of gate voltage.
Q.107 In a MOD-10 counter, what is the count sequence after 9?
A. 0
B. 15
C. 10
D. 1
Answer: A. 0
Explanation:
A MOD-10 counter counts from 0 to 9. After reaching 9, the next clock pulse resets the counter to 0, starting a new cycle.
Q.108 What is the impact of a line-to-line fault on the voltage in the faulted phases?
A. Voltage in all phases becomes equal.
B. Voltage in the faulted phases becomes zero.
C. Voltage in the faulted phases increases.
D. Only the unaffected phase experiences a voltage drop.
Answer: B. Voltage in the faulted phases becomes zero
Explanation:
A line-to-line fault creates a short circuit between two phases. At the fault point, the voltage difference between the faulted phases drops to zero, causing a severe voltage collapse in those phases.
Q.109 The standard form of characteristics equation of the second order system transfer function is an equation which includes:
A. damping factor and open loop zeros only
B. both natural frequency and damping factor
C. natural frequency only
D. neither natural frequency nor damping factor
Answer: B. both natural frequency and damping factor
Explanation:
The standard characteristic equation of a second-order system is:
( s^2 + 2\zeta\omega_n s + \omega_n^2 = 0 )
It includes both the natural frequency (( \omega_n )) and the damping ratio (( \zeta )), which define the system’s transient response.
Q.110 Which of the following is the unit of the Poynting vector?
A. Watts per metre (W/m)
B. Watts per square metre (W/m²)
C. Volt per square metre (V/m²)
D. Ampere per square metre (A/m²)
Answer: B. Watts per square metre (W/m²)
Explanation:
The Poynting vector (( \vec{S} )) represents power flow per unit area in an electromagnetic field. Its unit is Watts per square metre (W/m²), indicating the rate of energy transfer through a surface.
Q.111 Select the correct option based on the given statements.
Statement 1: In a balanced three-phase system, the phase voltage is the voltage measured between any one phase and the neutral.
Statement 2: The line voltage is the voltage measured between any two phases.
A. Both Statement 1 and Statement 2 are true.
B. Statement 1 is false, Statement 2 is true.
C. Statement 1 is true, Statement 2 is false.
D. Both Statement 1 and Statement 2 are false.
Answer: A. Both Statement 1 and Statement 2 are true
Explanation:
In a balanced three-phase system, the phase voltage is measured between a single phase conductor and neutral, while the line voltage is measured between any two phase conductors. These definitions are fundamental to three-phase power systems.
Q.112 The power factor (pf) of an AC circuit is defined as the ratio of:
A. real power to reactive power
B. apparent power to real power
C. reactive power to apparent power
D. real power to apparent power
Answer: D. real power to apparent power
Explanation:
Power factor is defined as ( \text{pf} = \frac{\text{Real Power (P)}}{\text{Apparent Power (S)}} ). It indicates how effectively the power is being used. A higher power factor means more efficient power usage.
Q.113 If ( K_p ) denotes the position error constant, then the steady state error of a second order control system for step input is defined as:
A. ( \frac{1}{1 + K_p} )
B. ( \frac{1}{1 + K_p} )
C.
D. ( [1 + K_p] )
Answer: B. ( \frac{1}{1 + K_p} )
Explanation:
For a unit step input, the steady-state error ( e_{ss} ) is given by:
( e_{ss} = \frac{1}{1 + K_p} ),
where ( K_p ) is the position error constant. This formula applies to Type-1 systems.
Q.114 Which of the following is NOT a typical application of flip-flops?
A. Phase shifting
B. Digital storage
C. Analog signal amplification
D. Frequency division
Answer: A. Phase shifting
Explanation:
Flip-flops are used in digital storage, frequency division, and sequential logic. They are not typically used for phase shifting, which is more relevant to analog signal processing.
Q.115 In a circuit with three resistors in series, if the current through the circuit is 2 A and the resistors have values of 3 Ω, 5 Ω and 7 Ω, respectively, what is the total voltage across the loop according to KVL?
A. 10 V
B. 30 V
C. 15 V
D. 20 V
Answer: B. 30 V
Explanation:
Total resistance: ( R = 3 + 5 + 7 = 15 \Omega )
Using Ohm’s Law: ( V = IR = 2 \times 15 = 30 \text{ V} )
According to KVL, the total voltage drop equals the supply voltage, which is 30 V.
Q.116 A capacitive filter is used to filter out the AC component of a rectified voltage. The filter consists of a capacitor C connected in parallel with a load resistor ( R_L ). If the rectified voltage has a peak value of ( V_P ) and a frequency of ( f ), what is the effect of increasing the value of the capacitor C on the ripple voltage ( V_R )?
A. The ripple voltage ( V_R ) decreases
B. The ripple voltage ( V_R ) becomes zero
C. The ripple voltage ( V_R ) increases
D. The ripple voltage ( V_R ) remains the same
Answer: A. The ripple voltage ( V_R ) decreases
Explanation:
Increasing the capacitance allows the capacitor to store more charge, which helps maintain voltage during discharge periods, thereby reducing ripple voltage and producing a smoother DC output.
Q.117 In an IGBT, the control terminal is called the:
A. collector
B. emitter
C. base
D. gate
Answer: D. gate
Explanation:
An IGBT is a voltage-controlled device. The gate terminal controls its operation, while the collector and emitter carry the main current. It combines features of MOSFETs and BJTs.
Q.118 For a two-sided sequence ( x[n] ), which of the following statements about the ROC of its Z-transform is correct?
A. The ROC lies between two poles.
B. The ROC is always ( |z| < r ).
C. The ROC does not exist for two-sided sequences.
D. The ROC is always ( |z| > r ).
Answer: A. The ROC lies between two poles
Explanation:
For a two-sided sequence, the ROC is an annular region:
( r_1 < |z| < r_2 ),
bounded by the poles of the left-sided and right-sided components.
Q.119 What is the effect of time-scaling ( x[an] ) on the Z-Transform?
A. ( X(z^{1/a}) )
B. ( z^a X(z) )
C. ( X(az) )
D. ( X(z)/a )
Answer: A. ( X(z^{1/a}) )
Explanation:
The time-scaling property of the Z-transform states:
If ( x[n] \rightarrow X(z) ), then ( x[an] \rightarrow X(z^{1/a}) ).
This reflects how scaling the time index affects the frequency domain.
Q.120 Which of the following equations shows that the time varying ( \vec{E} ) field is not conservative?
A. ( \nabla \times \vec{H} = \vec{J} )
B. ( \nabla \cdot \vec{D} = \rho_v )
C. ( \nabla \times \vec{E} = -\frac{\partial \vec{B}}{\partial t} )
D. ( \nabla \cdot \vec{B} = 0 )
Answer: C. ( \nabla \times \vec{E} = -\frac{\partial \vec{B}}{\partial t} )
Explanation:
This is Faraday’s Law of Induction, which shows that a time-varying electric field has a non-zero curl, making it non-conservative. Static fields have zero curl, but changing magnetic fields induce circulating electric fields.