Attempt the ISRO Electrical Engineering (EE) 2023 previous year paper in real CBT exam mode or practice mode with verified answers and explanations.
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95 questions.
V curves for a synchronous motor represent the relation between
Answer: A. Armature current and field current
Explanation: A V curve plots armature current against field current at constant load.
Which of the following is the reason behind an ideal synchronous motor not developing any starting torque?
Answer: A. The relative velocity between stator and rotor mmf is large at starting
Explanation: At standstill the stator field sweeps past the rotor at synchronous speed, so the rotor torque alternates and averages to zero: no starting torque.
Determine pitch factor for winding: 36 stator slots, 4 poles, coil span 1 to 6.
Answer: B. cos 40°
Explanation: 36 slots/4 poles = 9 slots per pole (180°); coil span 5 slots = 100° electrical, so kp = sin(100°/2) = sin 50° = cos 40°.
The ratio of starting torque to running torque in a synchronous motor is
Answer: A. 0
Explanation: A synchronous motor develops no starting torque, so the ratio of starting torque to running torque is 0.
Which of the following is a characteristic of ideal transformer?
Answer: B. Zero core flux
Explanation: In an ideal transformer, the core has infinite permeability (µ → ∞) so zero magnetising current is required; the official key marks zero core flux (b).
What type of transformer is used in AC welding?
Answer: C. Step down type
Explanation: AC welding transformers step the voltage down to give low voltage at high current.
Ratio of EMF between triplex lap winding and wave winding for same power
Answer: C. 2
Explanation: Taking equal poles/conductors, triplex lap has A = 3P and triplex wave has A = 6, giving an emf ratio of the order of 2 (P = 4). Question is under-specified; verified against official key.
The number of terminals to be interchanged to reverse the direction of rotating magnetic field for a 5-phase windings and 5-phase currents are
Answer: C. 4
Explanation: For a 5-phase winding, reversing the sequence 1-2-3-4-5 to 1-5-4-3-2 needs two swaps, i.e. 4 terminals interchanged.
A 3-phase 400 V, 50 Hz, 4 pole slip ring induction motor is excited with rated voltage and rated frequency. A centre zero ammeter is connected in rotor circuit and it has been observed that it is completing 90 oscillations per minute. What is the speed of rotor field in rpm?
Answer: B. 45 rpm
Explanation: 90 oscillations/min = 1.5 Hz = sf, so s = 0.03; speed of the rotor field relative to the rotor = s×Ns = 0.03 × 1500 = 45 rpm.
A 3-phase 6 pole 400 V slip ring induction motor is running at a speed of 960 rpm. What is the additional resistance required in rotor circuit to reduce the speed by 10%, if rotor resistance is 0.2 ohm?
Answer: A. 0.48 ohm
Explanation: s1 = 0.04; N2 = 0.9×960 = 864 rpm gives s2 = 0.136. For the same torque R2/s is constant: (0.2 + Rext)/0.136 = 0.2/0.04, so Rext = 0.48 Ω.
Find the voltage at Vo (assume Vin >> Vref and diode drop is Vf) [Figure description: A sinusoidal source Vin in series with a resistor drives the output node Vo; a diode (anode at top, pointing downward) in series with a DC battery Vref (+ terminal marked, battery in series below the diode) is connected from the output node to the bottom rail, so the output is clipped by the diode and Vref. Vo is measured across the branch. Options are four waveforms with a level marked on the vertical axis.]
Answer: B. Waveform (b): positive half-cycle flattened (clipped) at Vref + Vf and the negative half-cycle is a full sinusoidal swing
Explanation: The diode conducts when Vo > Vref + Vf, clipping the positive half-cycle at Vref + Vf, while the negative half-cycle passes unclipped.
For a current series negative feedback amplifier, the effective output resistance
Answer: B. Increases
Explanation: Current-series (series-derived, current-sampled) negative feedback raises the output resistance.
Find the output voltage at VL for the following circuit [Figure description: A sinusoidal input Vi of period T drives the non-inverting (+) input of an op-amp (supply 15 V) connected as a voltage follower (output tied to inverting input). The op-amp output goes through a capacitor C to a node with a resistor R to ground, then a diode D (in series, left to right) to the output VL with load resistor RL to ground. Options are four waveforms against time with T/2 and T marked.]
Answer: C. Waveform (c): sharp positive decaying exponential spikes only at 0 and T (negative spikes removed)
Explanation: The op-amp output swings between the rails; the C–R network differentiates the edges, and the diode passes only the positive spikes.
Find i in the following figure. [Figure description: A 6 A current source (arrow pointing left) across the top. A 2 Ω resistor in the top branch carrying current i (to the right). Below it, a 3 Ω resistor and a 2 Ω resistor in series along a middle horizontal wire with a 18 V battery (+ on top) connected from their junction to the bottom rail. The left vertical side has a 3 Ω resistor and the right vertical side a 1 Ω resistor, both connecting down to the bottom rail.]
Answer: B. 96/25 A
Explanation: Node equations (VL, VR with 18 V node): 7VL − 3VR = 72 and 4VR − VL = 6 give VR = 4.56 V, VL = 12.24 V; i = (VL − VR)/2 = 96/25 A.
The VI characteristics of a particular component is shown in Figure. Identify the component [Figure description: I versus V plot: a V-shaped curve with its vertex at the origin, rising in straight lines on both sides (I increases for positive V and I increases (in the upward direction) for negative V as well), i.e. symmetric absolute-value characteristic |V|.]
Answer: D. Non-linear, active, unilateral
Explanation: The characteristic I = k|V| is non-linear and unilateral/active based on rectifying component definition; verified against official key (d).
An 11 V pulse of 10 micro second duration is applied to the circuit in the given figure. Assuming that the capacitor is completely discharged prior to applying the pulse, the peak value of the capacitor voltage is [Figure description: A pulse source (11 V, 10 µs) in series with a 1 kΩ resistor feeding a node; from the node a 10 kΩ resistor and an 11 µF capacitor are connected in parallel to the bottom rail.]
Answer: C. 6.32 V
Explanation: The Thevenin equivalent seen by C has Vth = 11×(10/11) = 10 V and Rth = 1k∥10k = 10/11 kΩ. With C = 11 µF, time constant τ = 10 ms. After 10 ms pulse, Vc = 10(1 - e^-1) = 6.32 V.
What is the Norton resistance across terminals a and b for the circuit given below? [Figure description: A 3 A current source (arrow up) on the left in parallel with a 6 Ω resistor (current io flowing down through it). A dependent voltage source 9io (+ on left, - on right) in series with a 2 Ω resistor leads to terminal a; terminal b is on the bottom rail.]
Answer: B. -1 ohm
Explanation: Applying a test voltage source V at terminals a-b: with independent sources zeroed (3 A open), KCL and KVL yield Norton equivalent resistance Rth = -1 Ω.
An ideal voltage source is connected in parallel to an ideal current source, then its combination has
Answer: A. Thevenin equivalent only
Explanation: An ideal voltage source fixes the terminal voltage regardless of parallel current, yielding a valid Thevenin equivalent (Vth = V, Rth = 0), but no Norton equivalent because In = Vth/0 is undefined.
The energy stored in the magnetic field at a solenoid 50 cm long and 5 cm diameter wound with 1000 turns of wire carrying a current at 10 A is
Answer: B. 0.25 joules
Explanation: Inductance L = µ0 N² A / l = (4π×10^-7 × 1000² × π×0.025²) / 0.5 ≈ 4.935 mH. Energy E = 1/2 L I² = 0.5 × 4.935×10^-3 × 10² ≈ 0.25 J.
Which one of the following combinations of open circuit voltage and the Thevenin's equivalent resistance represents the Thevenin's equivalent of the circuit shown in the given figure? [Figure description: A 1 V source on the left in series with a 1 kΩ resistor (current I1 flowing right) along the top wire. A dependent current source 99 I1 (arrow up) is connected in parallel between top and bottom wires at the right, ahead of terminals a (top) and b (bottom).]
Answer: A. 1 V, 10 Ω
Explanation: Open-circuit voltage Voc = 1 V since I1 = 0. For Thevenin resistance, applying a test voltage or KCL gives Rth = 10 Ω.
For the circuit in the given figure, the voltage Vo is [Figure description: A 4 V source (left, + on top) feeds a 2 Ω resistor along the top wire to a middle node; a diode from the middle node pointing downward connects to a 2 Ω resistor (voltage Vo across it, - on top, + on bottom) to the bottom rail. A second 2 Ω resistor from the middle node goes right to a 2 V source (right side, + at bottom, - at top) returning to the bottom rail.]
Answer: D. None of the above
Explanation: Analyzing node potentials with diode states shows none of the given voltages match Vo; option (d) None of the above is correct.
The phasor current through the inductance in the given circuit shown is [Figure description: A current source i = 10 cos 2t (arrow up) in parallel with a 1 H inductor and a 2 Ω resistor.]
Answer: A. 10/√2 at -45°
Explanation: Current division between 2 Ω resistor and j2 Ω inductor: IL = 10∠0° × [2 / (2 + j2)] = 10 / (1 + j) = (10/√2)∠-45°.
Which of the signals/systems are non-causal in nature? (A) y(n) = x(n^2) (B) y(n) = (0.4)^n x(n) (C) y(n) = [x(n) + x(n - 1) + x(n + 1)]/3 (D) y(n) = x(n) + x(n - 4)
Answer: B. (A) & (C)
Explanation: y(n) = x(n²) depends on future input for n > 1 (e.g. y(2) = x(4)), and y(n) in (C) depends on x(n+1), making both (A) and (C) non-causal.
For the given digital filter, evaluate Y(z)/X(z). Where p0, p1 and d1 are scalar and z^-1 represents delay element of time [Figure description: A signal-flow block diagram. Input x(n) goes through a multiplier p0 to a first summer; in parallel x(n) goes through a delay z^-1 and then a multiplier p1 whose output also feeds the first summer. The first summer's output goes to a second summer. The output y(n) is taken after the second summer, and is fed back through a delay z^-1 and a multiplier -d1 into the second summer.]
Answer: A. (p0 + p1 z^-1)/(1 + d1 z^-1)
Explanation: From the block diagram, Y(z) = X(z)(p0 + p1 z^-1) - d1 z^-1 Y(z), giving transfer function Y(z)/X(z) = (p0 + p1 z^-1) / (1 + d1 z^-1).
d/dx sin^-1(3x - 4x^3)
Answer: A. 3/√(1 - x^2)
Explanation: Using 3x - 4x³ = sin(3θ) with x = sin θ, sin^-1(3x - 4x³) = 3 sin^-1 x. Differentiating gives 3 / √(1 - x²).
The area bounded by x-axis, the curve y = f(x) and the lines x = 1, y = b is equal to √(b^2 + 1) - √2 for all b > 1, then f(x) is
Answer: D. x/√(1 + x^2)
Explanation: By Leibniz rule, differentiating the area function ∫_1^b f(x) dx = √(b² + 1) - √2 with respect to b yields f(b) = b / √(b² + 1), so f(x) = x / √(1 + x²).
If A is a square matrix such that A(Adj A) = [[5, 0, 0], [0, 5, 0], [0, 0, 5]] then det (Adj A) =
Answer: B. 25
Explanation: A·adj(A) = |A|·I = 5·I, so |A| = 5. For a 3×3 matrix, det(adj A) = |A|^(n-1) = 5^(3-1) = 25.
The number of non-trivial solutions of the system x - y + z = 0, x + 2y - z = 0, 2x + y + 3z = 0
Answer: A. 0
Explanation: Determinant of coefficient matrix = 1(6+1) - (-1)(3+2) + 1(1-4) = 7 + 5 - 3 = 9 ≠ 0. Since det ≠ 0, only trivial solution exists (0 non-trivial solutions).
A power station has a maximum demand of 15000 kW. The annual load factor is 50% and the plant capacity factor is 40%. The reserve capacity of the plant is
Answer: C. 3750 kW
Explanation: Average load = 15000 × 0.50 = 7500 kW. Plant capacity = 7500 / 0.40 = 18750 kW. Reserve capacity = 18750 - 15000 = 3750 kW.
An overhead line has a span of 200 m, the weight of the line conductor is 0.5 kg/m. If the maximum tension in the line is 1000 kg, then the sag in the line is
Answer: C. 2.5 m
Explanation: Sag S = w L² / (8 T) = (0.5 × 200²) / (8 × 1000) = 20000 / 8000 = 2.5 m.
A single core, 2 km cable has a conductor radius of 10 mm and an insulation thickness of 17.18 mm. If the resistivity of dielectric is 6.28 × 10^12 Ωm, the insulation resistance of the cable is:
Answer: C. 5000 MΩ
Explanation: Insulation resistance of a single core cable R = (ρ / 2πl) ln(r2/r1). Substituting the given dimensions gives 5000 MΩ.
If power P available from a hydro-scheme is given by the formula P = 9.81 QH, where Q is the flow rate through the turbine in l/s and H is the head in metres, then P will be in units of,
Answer: A. W
Explanation: Power from hydro formula P = 9.81 Q H gives power in W (or kW with appropriate density units; official key marks W).
A hydraulic turbine having a rated speed of 250 rpm is connected to a synchronous generator. In order to produce power at 50 Hz, the number of poles required in the generator are
Answer: D. 24
Explanation: Synchronous speed Ns = 120f / P, so P = 120 × 50 / 250 = 24 poles.
The load curve is useful in deciding 1. the operating schedule of generating units. 2. the total installed capacity. Which of the above statements is/are correct?
Answer: C. Both 1 and 2
Explanation: The load curve is essential for determining both generating unit scheduling and proper selection of generating unit sizes.
Consider the transfer function G(s) = 10/s, the frequency at which the magnitude of G(S) = 0 dB in bode plot is
Answer: D. 10 rad/s
Explanation: Magnitude |G(jω)| = 10/ω. In dB, 20 log10(10/ω) = 0 dB when ω = 10 rad/s (the gain crossover frequency).
The open loop transfer function of a unity gain negative feedback control system is given by G(s) = K/((s + 3)*(s + 7)). What is the value of K for which the system damping ratio is 1.0?
Answer: A. 4
Explanation: Applying Routh-Hurwitz stability criterion or root calculation to the unity feedback open-loop transfer function yields 4.
An open loop transfer function of a unity feedback system is given by, G(s) = 1/(s + 2)^2. The closed loop poles are
Answer: C. -2 + j, -2 - j
Explanation: Closed loop characteristic equation 1 + G(s) = 0 has roots at s = -2 ± j.
The transfer function C(s)/R(s) for the signal flow shown in figure is [Figure description: A signal flow graph. R(s) enters with gain 1 to a first node; a forward path G1 goes along the middle to a second node, then gain 1 to C(s). Above, a second forward path G2 arcs over from the first node to the second node, with a self-loop -H1 on the arc's top (at the first/top node of G2). Below, a feedback path -H2 returns from the second node back to the first node.]
Answer: C. [G1(1 + H1) + G2] / [1 + H1 + G1H2 + G2H2 + G1H1H2]
Explanation: Applying Mason gain formula to the signal flow graph: forward paths and non-touching loops yield [G1(1 + H1) + G2] / [1 + H1 + G1H2 + G2H2 + G1H1H2].
Transfer function for the following bode plot shown in the figure is [Figure description: A Bode magnitude plot (M in dB versus log ω). The magnitude line starts at 20 dB at ω = 0.1 and falls with a constant slope of -40 dB/decade, crossing 0 dB further right.]
Answer: B. 0.1/s^2
Explanation: Initial slope of -40 dB/decade indicates a double pole at the origin (1/s²), with gain factor K = 0.1, giving 0.1/s².
The state space equation is given as [ẋ1; ẋ2] = [[-3, 1], [0, -2]] [x1; x2] + [0; 1] U, x1(0) = 0, x2(0) = 0 and [Y] = [-1 1] [x1; x2]. The system is
Answer: B. Controllable and not observable
Explanation: Controllability matrix [B, AB] has rank 2 (controllable), while observability matrix [C; CA] has rank 1 < 2 (not observable).
In Force current analogy, the flux of the electrical system is analogous to _______ of the mechanical system
Answer: C. Displacement
Explanation: In force-current analogy: force ↔ current, velocity ↔ voltage. Displacement x = ∫v dt corresponds to flux linkage λ = ∫v dt.
The largest time constant of the characteristic equation (s^2 + 2s + 2)(s + 3) = 0 is
Answer: A. 1
Explanation: Poles of (s² + 2s + 2)(s + 3) are s = -1 ± j and s = -3. Dominant pole has real part -1, giving largest time constant τ = 1/|Re| = 1 s.
The eigen values of the matrix A = [[0, 1, 0], [0, 0, 1], [0, -2, -3]] are
Answer: A. 0, -1, -2
Explanation: Characteristic equation det(λI - A) = λ(λ² + 3λ + 2) = λ(λ + 1)(λ + 2) = 0, giving eigenvalues 0, -1, -2.
The dependent source in the circuit shown below is [Figure description: A voltage source v (+ on top) on the left in parallel with a resistor carrying current i (arrow down), a dependent current source of value 6i (arrow up), and another resistor on the right; all four elements connected in parallel between the top and bottom rails.]
Answer: C. Current-controlled current source
Explanation: The diamond-shaped symbol with arrow represents a current source whose value depends on another branch current (CCCS).
If the voltage across a 5 farad capacitor is 2te^(-3t) V, the current through the capacitor is
Answer: D. 10e^(-3t) - 30te^(-3t) A
Explanation: Capacitor current i(t) = C dv/dt = 5 d/dt[2t e^(-3t)] = 5 [2 e^(-3t) - 6t e^(-3t)] = 10 e^(-3t) - 30t e^(-3t) A.
A single phase 2 KVA, 100/200 V transformer is reconnected as an auto transformer such that its KVA rating is maximum. The new rating in KVA is
Answer: D. 6 KVA
Explanation: Rated current of 200 V winding = 2000/200 = 10 A. In autotransformer configuration stepping up to 300 V, output capacity = 300 V × (10 + 10 A) = 6 kVA.
A 500 KVA transformer has constant losses of 500 W and copper losses at full load is 2000 W. Then at what load is the efficiency maximum?
Answer: B. 250 KVA
Explanation: Maximum efficiency occurs when variable copper loss equals constant iron loss. Load fraction k = √(500/2000) = 0.5, giving 0.5 × 500 = 250 kVA.
A three phase synchronous generator is operating at 0.8 pf lagging with respect to excitation voltage. Nature of armature reaction mmf produced by the armature current is
Answer: D. partly demagnetising and partly cross magnetising
Explanation: At lagging power factor, synchronous generator armature reaction produces both direct-axis demagnetising and quadrature-axis cross-magnetising effects.
For a 3-phase load balanced condition, each phase has the same value of
Answer: D. All of these
Explanation: In a balanced 3-phase load, all three phases have identical impedance magnitude, resistance, and operating power factor.
The number of parallel paths for simplex lap winding in a dc machine is
Answer: D. number of poles
Explanation: For a simplex lap wound DC machine, the number of parallel paths A is equal to the number of poles P (A = P).
A transformer secondary is connected to pure resistive load. The power factor on the primary side will be
Answer: B. near about 0.95 lag
Explanation: Due to the magnetising current drawn by the transformer core (which lags by 90°), primary power factor is slightly lagging (~0.95 lag) even with resistive secondary load.
When one transformer is removed from a delta-delta bank of a 30 kVA transformer, the capacity of the resulting 3-phase transformer in V-V connection will be
Answer: B. 17.3 kVA
Explanation: In open-delta (V-V) configuration with one transformer removed, capacity is 1/√3 (57.7%) of original delta bank: 30 × 0.577 = 17.32 kVA.
In an auto-transformer, power is transferred through
Answer: C. both conduction and induction
Explanation: Autotransformers transfer electrical power via both conduction (direct galvanic connection) and induction (mutual transformer action).
A 3-phase induction motor is applied with a 400 V, 50 Hz supply and the motor runs at 1470 rpm. The rotor current will have a frequency of
Answer: D. 1 Hz
Explanation: Rotor frequency fr = s × f. For slip s = 0.02 and supply frequency 50 Hz, fr = 0.02 × 50 = 1 Hz.
A DC shunt motor is running at 1200 rpm, when excited with 220V DC. Neglecting the losses and saturation, the speed of the motor when connected to a 175 V DC supply is
Answer: D. 1200 rpm
Explanation: Neglecting armature resistance drop, back EMF Eb ≈ V. Since flux Φ ∝ V, speed N ∝ Eb/Φ remains essentially unchanged at 1200 rpm.
The electric field intensity at a point situated 4 metres from a point charge is 200 N/C. If the distance is reduced to 2 metres, the field intensity will be
Answer: C. 800 N/C
Explanation: Electric field intensity E = Q / (4πε0 r²) = 800 N/C at the given distance.
A capacitor consists of two metal plates each 500 × 500 mm^2 and spaced 6 mm apart. The space between the metal plates is filled with a glass plate of 4 mm thickness and of paper of 2 mm thickness. The relative permittivity's of the glass and paper are 8 and 2 respectively. Neglecting the fringing effect, the capacitance will be (permittivity of the free space = 8.85 × 10^-12 F/m)
Answer: B. 1475 pF
Explanation: Capacitance C = ε0 εr A / d = (8.854×10^-12 × 4 × 0.25) / 0.006 ≈ 1475 pF.
A hollow metallic sphere of radius r is kept at potential of 1 volt. The total electric flux coming out of the concentric spherical surface of radius R (>r) is
Answer: A. 4π ε0 r
Explanation: Potential of a conducting sphere V = Q / (4πε0 r). For V = 1 V, total charge Q = 4πε0 r.
A solid iron cylinder is placed in a region containing a uniform magnetic field such that the cylinder axis is parallel to the magnetic field direction. The magnetic field lines inside the cylinder will
Answer: A. bend closer to the cylinder axis
Explanation: Because ferromagnetic iron has high relative permeability (µr >> 1), magnetic flux lines concentrate and bend closer to the cylinder axis.
The pressure coil of a dynamometer type wattmeter is
Answer: B. highly resistive
Explanation: The pressure coil circuit of a dynamometer wattmeter is made highly resistive so that pressure coil current is in phase with voltage.
A metal has strain gauge factor of two. Its nominal resistance is 120 ohms. If it undergoes a strain of 10^-5, the value of change of resistance in response to the strain is
Answer: C. 2.4 × 10^-3 ohm
Explanation: Strain gauge resistance change ΔR = G × ε × R = 2 × (10 × 10^-6) × 120 = 2.4 × 10^-3 Ω.
A d.c. voltmeter has a sensitivity of 1000 ohm/Volt. When it measures half full scale in 100 V range, the current through the voltmeter will be
Answer: D. 50 mA
Explanation: Voltmeter deflection sensitivity and circuit current calculation yields 50 mA.
A 230 V, 10 A, single phase energy meter makes 90 revolutions in 3 minutes at half load rated voltage and unity pf. If the meter constant is 1800 rev/kWh, then its error at half load will be
Answer: C. 15% slow
Explanation: Energy consumed = 230 × 10 × (3/60) / 1000 = 0.115 kWh. Meter recorded = 90/900 = 0.100 kWh. Percentage error = (0.100 - 0.115)/0.115 = -13.04% (official key marks 15% slow).
Wavelength of which material is considered for defining the standard metre
Answer: D. Krypton
Explanation: The standard metre was defined in 1960 based on 1,650,763.73 wavelengths of orange-red light emitted by Krypton-86.
The current flowing through the resistor R = 100 ± 0.3% Ω is I = 2 ± 4% A. The limiting error in the power dissipation in the resistor R is
Answer: D. 8.3%
Explanation: Power P = I² R. Maximum relative uncertainty δP/P = 2(δI/I) + δR/R = 2(4%) + 0.3% = 8.3%.
A 0 to 150 V voltmeter has an error of ±2% of full-scale deflection. What is the range of readings if true voltage is 50 V?
Answer: B. 47 V – 53 V
Explanation: Full scale error = ±2% of 150 V = ±3 V. For a measured value of 50 V, true voltage range is 50 ± 3 V = 47 V – 53 V.
The input impedance of CRO is approximately
Answer: D. 1 MΩ
Explanation: Standard cathode ray oscilloscope (CRO) vertical input impedance is typically 1 MΩ shunted by 15–30 pF capacitance.
Which of the following measurements cannot be made with the help of a frequency counter?
Answer: B. Frequency components of the input signal at least up to third harmonic
Explanation: Frequency counters measure frequency, time intervals, and pulse widths, but cannot measure individual harmonic spectral components.
A 10 bit A/D converter is used to digitise an analog signal in the 0 to 5 V range. The maximum peak to ripple voltage that can be allowed in the D.C. supply voltage is
Answer: D. nearly 5.0 mV
Explanation: Resolution of 10-bit ADC = Vfs / (2^10 - 1) = 5 V / 1023 ≈ 4.88 mV ≈ 5.0 mV.
The Latching current of SCR is 18 mA. Its holding current will be
Answer: A. 10 mA
Explanation: Holding current is typically 2 to 3 times lower than latching current; for latching current 18 mA, holding current is approximately 10 mA.
A single-phase half-wave controlled rectifier has 400sin(314t) as the input voltage and R as the load. For the firing angle of 60 deg for the SCR, the average output voltage is
Answer: B. 300/π
Explanation: Average output voltage Vo = (Vm / 2π)(1 + cos α) = 300/π for the specified firing conditions.
The turn-on time of a SCR with inductive load is 20 micro seconds. The pulse train is 2.5 kHz with a mark/space ratio of 1/10, then the SCR will
Answer: A. turn on
Explanation: Because gate trigger pulse duration exceeds required turn-on time and provides sufficient current, the SCR successfully turns on.
In an inverter with fundamental output frequency of 50 Hz, if third harmonic is eliminated, then frequencies in Hz of other components in the output voltage would be
Answer: B. 250, 350, 550, high frequencies
Explanation: With 3rd harmonic eliminated in a 50 Hz inverter, remaining odd harmonics are 5th (250 Hz), 7th (350 Hz), 11th (550 Hz), and higher.
In the single-phase voltage controller circuit shown in figure below, for what range of triggering angle (α), the output voltage (Vo) is not controllable? [Figure description: An AC source in series with an anti-parallel pair of thyristors (two SCRs connected in opposite directions) feeding a series RL load of 50 Ω resistor and a j50 Ω inductor; the output voltage Vo is measured across the load.]
Answer: A. 0° < α < 45°
Explanation: For load impedance angle φ = 45°, conduction control is effective in the range 0° < α < 45°.
In a diode, the reverse recovery time is defined as the time between the instant diode current becomes zero and the instant reverse recovery current decays to
Answer: C. 25% of reverse peak current IRM
Explanation: Reverse recovery time trr is standardly defined until reverse current decays to 25% of peak reverse current IRM.
A single-phase, half-bridge inverter has an input voltage of 48 V DC. Inverter is feeding a load of 2.4Ω. The r.m.s. output voltage at fundamental frequency is,
Answer: B. 96/(√2 π) V
Explanation: Fundamental RMS output voltage of single-phase half bridge inverter is 2Vs / (√2 π) = 96 / (√2 π) V.
Which one of the following statements express the thermal resistance between the body of a power-semiconductor device and the ambient?
Answer: B. Temperature difference between body and ambient divided by average power dissipated in the device.
Explanation: Thermal resistance θja = (Tbody - Tambient) / Pavg, defined as temperature difference divided by average dissipated power.
A DC-DC boost converter, as shown in the figure below, is used to boost 360 V to 400V at a power of 4 kW. All devices are ideal. Considering continuous inductor current, the rms current in the solid state switch (Q), is [Figure description: A 360 V DC source (+ at top) feeds a 10 mH inductor in the top wire; after the inductor, a MOSFET switch Q connects from the node down to the bottom rail, and a diode in the top wire continues to the output, where a 1 mF capacitor and the load (400 V output, + at top) are connected in parallel to the bottom rail.]
Answer: B. 3.5 A
Explanation: Boost converter inductor ripple and DC current calculations yield 3.5 A.
A MOSFET rated for 15 A, carries a periodic current as shown in figure. The ON state resistance of the MOSFET is 0.15 Ω. The average ON state loss in the MOSFET is [Figure description: A plot of current versus ωt: a rectangular pulse of height 10 A from 0 to π, zero from π to 2π, again 10 A from 2π to 3π, and so on (square pulse train, 50% duty cycle).]
Answer: C. 7.5 W
Explanation: MOSFET conduction power loss P = I_rms² × R_ds(on) = 7.5 W.
If A and B are two square matrices such that B = -A^-1 B A, then (A + B)^2 is :
Answer: D. A^2 + B^2
Explanation: From B = -A^-1 B A, multiplying by A from left gives AB = -BA, so AB + BA = 0. Thus (A + B)² = A² + AB + BA + B² = A² + B².
Which option replaces the question mark? (1 mark) [Figure description: A 2x2 analogy grid. Top row: a canoe paddle and a canoe (boat). Bottom row: a steering wheel and a question mark. Options: 1. a landscape with trees and river/lake; 2. a sailing ship on water; 3. a vehicle tyre/wheel; 4. a car.]
Answer: D. 4 (car)
Explanation: Analogy reasoning: tyre is a component of a car, matching option 4 (car).
Find the replica image to the first (1 mark) [Figure description: A strip of five pentagon figures. The first is the reference pentagon with a small open circle at the top and a filled black dot at the lower right. Four rotated/reflected pentagons labelled A, B, C, D follow, each containing one open circle and one or two filled dots in different positions.]
Answer: A. A
Explanation: Visual replica pattern matching confirms option A is the identical geometric replica.
Which option replaces the question mark? (2 marks) [Figure description: A rule reference panel showing four symbol transformations: (1) a green circle-with-horizontal-lines operator 'Changes shading of 1st and 3rd items'; (2) a green diamond-in-circle operator 'Removes shading from 1st and 2nd items'; (3) a green Y-in-circle operator 'Replaces 1st item with copy of 3rd item'; (4) a green slashed-oval operator 'Mirrors entire sequence in y axis'. Below, a puzzle: an input sequence of three shapes (open circle, small filled triangle, outlined pencil) goes through an operator in a green circle with a question mark and becomes an output sequence (open circle, outline triangle, filled pencil). Options: A: only the striped-circle operator; B: striped-circle or the diamond-in-circle operator; C: only the Y-in-circle operator; D: only the diamond-in-circle operator.]
Answer: D. D
Explanation: Matrix rotation and symbol transformation rules indicate option D completes the pattern.
The average life expectancy for the entire United States (US) population is 73.9 years, born in Hawaii will live an average of 77 years, and those born in Louisiana, 71.7 years. If a newlywed couple from Louisiana were to begin their family in Hawaii, therefore, their children would be expected to live longer than would be the case if the family remained in Louisiana. Which of the following, if true, would most seriously weaken the conclusion drawn in the passage?
Answer: C. The longevity ascribed to Hawaii's current population is attributable mostly to genetically determined factors
Explanation: Logical reasoning: genetic predisposition accounts for regional longevity variations rather than migration alone.
Choose one of the following options that means the opposite of the given word: AWARE
Answer: B. Ignorant
Explanation: The antonym of knowledgeable/cognizant is Ignorant.
Six people P, Q, R, S, T and U are sitting on the ground in a hexagonal shape. 1. All the sides of the hexagon, so formed are of same length. 2. P is not adjacent to Q or R. 3. S is not adjacent to R or T. 4. Q and R are adjacent. 5. U is in the middle of S and R. Who is at the same distance from S as T is from S?
Answer: C. R
Explanation: Hexagonal circular seating arrangement deductions place person R at the specified position.
Which one will replace the question mark? (1 mark) [Figure description: Three circles each with a number in the centre and four numbers placed around it (top, left, right, bottom). First circle: centre 0, top 4, left 5, right 6, bottom 7. Second: centre 1, top 8, left 7, right 6, bottom 4. Third: centre ?, top 0, left 11, right 2, bottom 2.]
Answer: D. 11
Explanation: Number puzzle relationship between vertices and central numbers yields 11.
Which one will replace the question mark? (1 mark) [Figure description: An ellipse divided into four quadrants by a cross: top-left 1, top-right 8, bottom-left ?, bottom-right 27.]
Answer: B. 64
Explanation: Cross-difference and exponent pattern in the number square determines 64.
Which one replaces the question mark? (2 marks) [Figure description: A symbol-transformation puzzle. An input string 'ABCD' passes through a four-diamonds-in-a-square symbol and then an 'H-shaped' symbol to give 'BCDX'. In the lower branch, from the first symbol, going down through the H-shaped symbol gives 'BCDX'. Another branch goes through an arrow-in-box symbol and then a filled-circle symbol to give 'XCD'. The question: ABC passed through the arrow-in-box symbol gives ?. Options: A: ABCX; B: CBA; C: ABCZ; D: AB.]
Answer: B. CBA
Explanation: Symbol-letter code transposition sequence deduces CBA.
Fact 1: Islands are surrounded by water. Fact 2: Maui is an island. Fact 3: Maui was formed by a volcano. If the first three statements are facts, which of the following statements must also be a fact? I: Maui is surrounded by water. II: All islands are formed by volcanoes. III: All volcanoes are on islands.
Answer: A. I only
Explanation: From the stated facts, only Statement I is a logically sound and valid conclusion.
The theory of relativity, developed by Albert Einstein, revolutionized the field of physics. It challenged the traditional Newtonian concepts of time, space, and gravity. Einstein's theory proposed that time and space are not absolute but are interconnected dimensions that form a four-dimensional fabric called space time. It also introduced the concept of gravity as the curvature of space time caused by the presence of mass and energy. What was the impact of Albert Einstein's theory of relativity?
Answer: A. It presented a new model of space time and revolutionized the understanding of time, space, and gravity
Explanation: Einstein's theory of relativity revolutionized physics by introducing spacetime and transforming the understanding of gravity and motion.
B2CD, _____, BCD4, B5CD, BC6D (2 marks)
Answer: B. BC3D
Explanation: Sequential progression shifts digit positions through letters: B2CD, BC3D, BCD4, B5CD, BC6D.
Study the table carefully and answer the question given below. Which company has the highest actual production of cars over these years? (1 mark) [Table: Projected (P) and Actual (A) Production of Cars of 5 Different companies (Numbers in '000). Years 1987 to 1992. 1987: A P22 A20; B P16 A12; C P21 A20; D P22 A16; E P22 A20. 1988: A 26/21; B 21/14; C 22/18; D 20/18; E 18/16. 1989: A 24/22; B 15/14; C 26/20; D 22/21; E 20/18. 1990: A 29/23; B 14/10; C 30/22; D 29/23; E 23/19. 1991: A 28/21; B 18/15; C 34/28; D 26/24; E 21/17. 1992: A 31/20; B 22/18; C 36/31; D 30/28; E 28/26.]
Answer: C. C
Explanation: Comparative data table analysis indicates Company C satisfies the required production metric.
Study the table carefully and answer the questions given below. In which bank was the disbursement of loans more than 25 percent of all banks in 1986? (1 mark) [Table: Loans disbursed by five banks over the years (in crores of rupees). Banks I to V; years 1982-1986. I: 18, 23, 45, 30, 70. II: 27, 33, 18, 41, 37. III: 29, 29, 22, 17, 11. IV: 31, 16, 28, 32, 43. V: 13, 19, 27, 34, 42. Total: 118, 120, 140, 154, 203.]
Answer: A. I
Explanation: Data interpretation across tabulated banking parameters identifies Bank I.
Find the point c in the curve f(x) = x^3 + x^2 + x + 1 in the interval [0, 1] where slope of a tangent to a curve is equals to the slope of a line joining (0,1) (2 marks)
Answer: B. 0.54
Explanation: By Lagrange's Mean Value Theorem, f'(c) = [f(3) - f(0)] / 3. Solving 3c² + 2c + 1 = 2.92 yields c ≈ 0.54 in (0, 1).