Previous Year Questions
85 questions — organised by subject with solutions and explanations.
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Two perfectly matched silicon transistor are connected as shown in figure. The value of the current I is
The input resistance of the circuit in figure is
The transconductance of the transistor shown in figure is 10 mS. The value of the input resistance is
Assuming that the diodes are ideal in figure, the current in diode is
In the active filter circuit shown in figure, if Q=1, a pair of poles will be realized with equal to
The current through the Zener diode in figure is
In the Schmitt trigger circuit shown in figure, if = 0.1V, the output logic low level ( ) is
The feedback used in the circuit shown in figure can be classified as
The value of R for which the PMOS transistor in figure will be biased in linear region is
In the system shown in figure, the input x(t)=sint. In the steady-state, the response y(t) will be
The block diagram of a closed loop control system is given by figure. The values of K and P such that the system has a damping ratio of 0.7 and an undamped natural frequency of 5 rad/sec, are respecti
The unit impulse response of a second order under-damped system starting from rest is given by The steady-state value of the unit step response of the system is equal to
The state variable description of a linear autonomous system is X=AX, where X is the two dimensional state vector and A is the system matrix given by . The roots of the characteristic equation are
For a tachometer, if is the rotor displacement in radians, e(t) is the output voltage and is the tachometer constant in V/rad/sec, then the transfer function, will be
For the equation, the number of roots in the left half of s-plane will be
The Nyquist plot of loop transfer function G(s)H(s) of a closed loop control system passes through the point (-1,j0) in the G(s)H(s) plane. The phase margin of the system is
For the block diagram shown in figure, the transfer function is equal to
The open loop transfer function of a unity feedback control system is given as The value of 'a' to give a phase margin of is equal to
A digit circuit which compares two numbers and is shown in figure. To get output Y = 0, choose one pair of correct input numbers.
The voltage comparator shown in figure can be used in the analog-to-digital conversion as
If the following program is executed in a microprocessor, the number of instruction cycle it will take from START to HALT is
The digital circuit shown in figure generates a modified clock pulse at the output. Choose the correct output waveform from the options given below.
The simplified form of the Boolean expression can be written as
The digital circuit using two inverters shown in figure will act as
The value of Z in figure, which is most appropriate to cause parallel resonance at 500 Hz is
In figure, the capacitor initially has a charge of 10 Coulomb. The current in the circuit one second after the switch S is closed will be
In figure, the admittance values of the elements in Siemens are = 0.5 + j0, = 0 - j1.5, = 0 + j0.3 respectively. The value of I as a phasor when the voltage E across the elements is 10 V is
The Z-matrix of a 2-port network as given by The element of the corresponding Y-matrix of the same network is given by
A galvanometer with a full scale current of 10 mA has a resistance of 1000 . The multiplying power (the ratio of measured current to galvanometer current) of 100 shunt with this galvanometer is
A single-phase load is connected between R and Y terminals of a 415 V, symmetrical, 3-phase, 4-wire system with phase sequence RYB. A wattmeter is connected in the system as shown in figure. The power
A 50 Hz, bar primary CT has a secondary with 500 turns. The secondary supplies 5 A current into a purely resistive burden of 1 . The magnetizing ampere-turns is 200. The phase angle between the primar
A dc potentiometer is designed to measure up to about 2 V with a slide wire of 300 mm. A standard cell of emf 1.18 V obtains balance at 600 mm. A test cell is seen to obtain balance at 680 mm. The emf
A moving iron ammeter produces a full scale torque of 240 Nm with a deflection of at a current of 10 A . The rate of change of self induction ( H/radian) of the instrument at full scale is
The circuit in figure is used to measure the power consumed by the load. The current coil and the voltage coil of the wattmeter have 0.02 and 1000 resistances respectively. The measured power compared
A moving coil of a meter has 100 turns, and a length and depth of 10 mm and 20 mm respectively. It is positioned in a uniform radial flux density of 200 mT. The coil carries a current of 50 mA. The to
A dc A-h meter is rated for 15 A, 250 V. The meter constant is 14.4 A-sec/rev. The meter constant at rated voltage may be expressed as
A CRO probe has an impedance of 500 in parallel with a capacitance of 10 pF. The probe is used to measure the voltage between P and Q as shown in figure. The measured voltage will be
A single-phase, 230 V, 50 Hz, 4-pole, capacitor-start induction motor had the following stand-still impedances. Main winding Auxiliary winding The value of the starting capacitor required to produce p
A 8-pole, DC generator has a simplex wave-wound armature containing 32 coils of 6 turns each. Its flux per pole is 0.06 Wb. The machine is running at 250 rpm. The induced armature voltage is
A hydraulic turbine having 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
Two 3-phase, Y-connected alternators are to be paralleled to a set of common bus bars. The armature has a per phase synchronous reactance of 1.7 and negligible armature resistance. The line voltage of
For a , 2-phase bipolar stepper motor, the stepping rate is 100 steps/second. The rotational speed of the motor in rpm is
The direction of rotation of a 3-phase induction motor is clockwise when it is supplied with 3-phase sinusoidal voltage having phase sequence A-B-C. For counter clockwise rotation of the motor, the ph
A rotating electrical machine having its self-inductances of both the stator and the rotor windings, independent of the rotor position will be definitely not develop
The following motor definitely has a permanent magnet rotor
For a given stepper motor, the following torque has the highest numerical value
For a linear electromagnetic circuit, the following statement is true
The synchronous speed for the seventh space harmonic mmf wave of a 3-phase, 8-pole, 50 Hz induction machine is
A 400 V, 15 kW, 4-pole, 50Hz, Y-connected induction motor has full load slip of 4%. The output torque of the machine at full load is
The armature resistance of a permanent magnet dc motor is 0.8 . At no load, the motor draws 1.5 A from a supply voltage of 25 V and runs at 1500 rpm. The efficiency of the motor while it is operating
The type of single-phase induction motor having the highest power factor at full load is
A 400 V, 50 kVA, 0.8 p.f. leading -connected, 50 Hz synchronous machine has a synchronous reactance of 2 and negligible armature resistance. The friction and windage losses are 2 kW and the core loss
A 500 kVA, 3-phase transformer has iron losses of 300 W and full load copper losses of 600 W. The percentage load at which the transformer is expected to have maximum efficiency is
A 50 kVA, 3300/230 V single-phase transformer is connected as an autotransformer shown in figure. The nominal rating of the auto- transformer will be
The resistance and reactance of a 100 kVA, 11000/400 V, -Y distribution transformer are 0.02 and 0.07 pu respectively. The phase impedance of the transformer referred to the primary is
A 500 MW, 3-phase, Y-connected synchronous generator has a rated voltage of 21.5 kV at 0.85 p.f. The line current when operating at full load rated conditions will be
A parallel plate capacitor is shown in figure. It is made two square metal plates of 400 mm side. The 14 mm space between the plates is filled with two layers of dielectrics of = 4, 6 mm thick and = 2
The inductance of a long solenoid of length 1000 mm wound uniformly with 3000 turns on a cylindrical paper tube of 60 mm diameter is
Figure shows a chopper operating from a 100 V dc input. The duty ratio of the main switch S is 0.8. The load is sufficiently inductive so that the load current is ripple free. The average current thro
The triggering circuit of a thyristor is shown in figure. The thyristor requires a gate current of 10 mA, for guaranteed turn-on. The value of R required for the thyristor to turn on reliably under al
The circuit in figure shows a full-wave rectifier. The input voltage is 230 V (rms) single-phase ac. The peak reverse voltage across the diodes and is
The triac circuit shown in figure controls the ac output power to the resistive load. The peak power dissipation in the load is
A bipolar junction transistor (BJT) is used as a power control switch by biasing it in the cut-off region (OFF state) or in the saturation region (ON state). In the ON state, for the BJT
A single-phase half-controlled rectifier is driving a separately excited dc motor. The dc motor has a back emf constant of 0.5 V/rpm. The armature current is 5A without any ripple. The armature resist
A MOSFET rated for 15 A, carries a periodic current as shown in figure. The ON state resistance of the MOSFET is 0.15 . The average ON state loss in the MOSFET is
A variable speed drive rated for 1500 rpm, 40 Nm is reversing under no load. Figure shows the reversing torque and the speed during the transient. The moment of inertia of the drive is
Figure shows a chopper. The device is the main switching device. is the auxiliary commutation device. is rated for 400 V, 60 A. is rated for 400 V, 30 A. The load current is 20 A. The main device oper
The circuit in figure shows a 3-phase half-wave rectifier. The source is a symmetrical, 3-phase four-wire system. The line-to-line voltage of the source is 100 V. The supply frequency is 400 Hz. The r
The rated voltage of a 3-phase power system is given as
For harnessing low variable waterheads, the suitable hydraulic turbine with high percentage of reaction and runner adjustable vanes is
The transmission line distance protection relay having the property of being inherently directional is
A 800 kV transmission line is having per phase line inductance of 1.1 mH/km and per phase line capacitance of 11.68 nF/km. Ignoring the length of the line, its ideal power transfer capability in MW is
Total instantaneous power supplied by a 3-phase ac supply to a balanced R-L load is
A new generator having = 1.4 pu [equivalent to (1.212 + j0.70) pu] and synchronous reactance ' ' of 1.0 pu on the system base, is to be connected to a bus having voltage in the existing power system.
A 50 Hz, 4-pole, 500 MVA, 22 kV turbo-generator is delivering rated megavoltamperes at 0.8 power factor. Suddenly a fault occurs reducing in electric power output by 40%. Neglect losses and assume con
The generalized circuit constants of a 3-phase, 220 kV rated voltage, medium length transmission line are If the load at the receiving end is 50 MW at 220 kV with a power factor of 0.9 lagging, then m
A 3-phase transmission line supplies -connected load Z. The conductor 'c' of the line develops an open circuit fault as shown in figure. The currents in the lines are as shown on the diagram. The posi
The phase sequences of the 3-phase system shown in figure is
A 500 MVA, 50 Hz, 3-phase turbo-generator produces power at 22 kV. Generator is Y-connected and its neutral is solidly grounded. It sequence reactances are pu and pu.It is operating at rated voltage a
In the thermal power plants, the pressure in the working fluid cycle is developed by
A 110 kV, single core coaxial, XLPE insulated power cable delivering power at 50 Hz, has a capacitance of 125 nF/km. If the dielectric loss tangent of XLPE is , then dielectric power loss in this cabl
A lightning stroke discharges impulse current of 10 kA (peak) on a 400 kV transmission line having surge impedance of 250 . The magnitude of transient over-voltage travelling waves in either direction
A 3-phase generator rated at 110 MVA, 11 kV is connected through circuit breakers to a transformer. The generator is having direct axis sub-transient reactance =19%, transient reactance =26% and synch