ISRO Electrical Engineering (EE) 2017 Question Paper & Solutions

Attempt the ISRO Electrical Engineering (EE) 2017 previous year paper in real CBT exam mode or practice mode with verified answers and explanations.

All ISRO Electrical Engineering (EE) papers

80 questions.

Question 1

An inductance of one H carrying a current of two amperes will store the energy of

  • A. 2 watts
  • B. 2 joules
  • C. 4 watts
  • D. 4 joules

Answer: B. 2 joules

Explanation: Magnetic energy stored in an inductor W = ½·L·I² = ½×1×2² = 2 J (joules).

Question 2

The square waveform of current has following relation between r.m.s value and average value

  • A. r.m.s. value of current is greater than the average value
  • B. r.m.s. value of current is less than the average value
  • C. r.m.s. value of current is equal to the average value
  • D. There is no definite relation between the r.m.s. value and average value for a square wave

Answer: C. r.m.s. value of current is equal to the average value

Explanation: For a symmetrical square wave of amplitude Im, |i(t)| = Im at all times, so Irms = Iavg = Im.

Question 3

Two numbers of 500 ohms one watt resistors are connected in parallel. Their combined resistance and wattage rating will be

  • A. 250 ohms, 1 watt
  • B. 250 ohms, 2 watts
  • C. 1000 ohms, 2 watts
  • D. 500 ohms, 2 watts

Answer: B. 250 ohms, 2 watts

Explanation: In parallel: Req = 500/2 = 250 Ω. Total power rating is the sum: 1 W + 1 W = 2 W.

Question 4

In a long uniform coil of inductance 2L and associated resistance 2R ohms is physically cut in to two exact halves which are rewound in parallel. The resistance and inductance of the combination are

  • A. R and L
  • B. 2R and 2L
  • C. R/2 and L/2
  • D. R/4 and L/4

Answer: C. R/2 and L/2

Explanation: Cutting a uniform coil of (2L, 2R) into two equal halves gives each half turns N/2 and length l/2, so each has L' = L and R' = R. Connecting them in parallel gives Leq = L/2 and Req = R/2.

Question 5

For transfer function of a physical two-port network

  • A. All zeros must lie only in the left half of the s-plane
  • B. All poles may lie anywhere in the s-plane
  • C. The poles lying on the imaginary axis must be simple
  • D. All the above

Answer: D. All the above

Explanation: For physical realizability and stability of a passive two-port network, transmission poles and zeros must lie in the LHP (or on the jω axis as simple poles), satisfying all these conditions.

Question 6

The starting torque of a three phase induction motor can be increased by

  • A. Increasing rotor reactance
  • B. Increasing rotor resistance
  • C. Increasing stator resistance
  • D. None of the above

Answer: B. Increasing rotor resistance

Explanation: Starting torque Tst ∝ R2/(R2² + X2²). Increasing rotor resistance R2 shifts the maximum torque toward standstill (s = 1), thereby increasing starting torque.

Question 7

The capacitor start-capacitor run single phase induction motor is operationally a

  • A. Single phase motor
  • B. Two phase motor
  • C. Three phase motor
  • D. A.C. series motor

Answer: B. Two phase motor

Explanation: Under running conditions, the two windings are displaced 90° in space with currents 90° apart in time, causing the motor to operate virtually as a balanced two-phase motor.

Question 8

What would happen if the field of a D.C. shunt motor is opened?

  • A. Speed will be reduced
  • B. Continue to run normally
  • C. Speed will enormously increase damaging the motor
  • D. None of the above

Answer: C. Speed will enormously increase damaging the motor

Explanation: For a DC shunt motor, speed N ∝ Eb/Φ. If the field circuit is opened, the flux Φ drops to the residual value (near zero), causing the speed to increase dangerously to destructive levels.

Question 9

Equalizer rings in D.C. generator with lap windings are used for

  • A. Equal distribution of current at brush for sparkless commutation
  • B. Prevention of harmonics
  • C. Reduction of noise and vibration
  • D. Avoiding overhang

Answer: A. Equal distribution of current at brush for sparkless commutation

Explanation: Equalizer rings connect points in a lap-wound armature that are at identical potentials, bypassing circulating currents away from the brushes and ensuring sparkless commutation.

Question 10

The Buchholz relay is normally used to protect the

  • A. Alternators against all internal faults
  • B. Oil immersed transformers against all internal faults
  • C. Synchronous motors against all internal faults
  • D. Transmission lines against all short circuit faults

Answer: B. Oil immersed transformers against all internal faults

Explanation: Buchholz relay is a gas-actuated protective device installed in the pipe connecting the tank and conservator of oil-immersed transformers to detect incipient and severe internal faults.

Question 11

The power transformer is a

  • A. Constant current device
  • B. Constant voltage device
  • C. Constant power device
  • D. Pulsating main flux device

Answer: D. Pulsating main flux device

Explanation: In a power transformer, the core flux is alternating and pulsating sinusoidally (Φ = Φm sin ωt) to induce alternating EMFs in the windings.

Question 12

A change of 5% in supply voltage to an induction motor will produce a change of approximately

  • A. 5% in the rotor torque
  • B. 7.5% in the rotor torque
  • C. 10% in the rotor torque
  • D. 25% in the rotor torque

Answer: C. 10% in the rotor torque

Explanation: Torque developed by an induction motor is proportional to V² (T ∝ V²). A 5% change in voltage produces ΔT/T ≈ 2(ΔV/V) = 2×5% = 10% change in rotor torque.

Question 13

If the supply frequency to the transformer is increased, the iron loss

  • A. Will increase
  • B. Will decrease
  • C. Will not change
  • D. May reach zero

Answer: A. Will increase

Explanation: Hysteresis loss Wh ∝ f·Bm^(1.6) and eddy current loss We ∝ f²·Bm². If supply voltage is not fixed or flux is maintained, core losses increase with frequency.

Question 14

The maximum temperature permitted for class A insulation is

  • A. 180 degree centigrade
  • B. 105 degree centigrade
  • C. 120 degree centigrade
  • D. None of the above

Answer: B. 105 degree centigrade

Explanation: Standard insulation temperature limits: Class Y = 90°C, Class A = 105°C, Class E = 120°C, Class B = 130°C, Class F = 155°C, Class H = 180°C, Class C > 180°C.

Question 15

Two transformers connected in parallel share load in the ratio of their KVA ratings, provided their ohmic impedance are

  • A. Equal
  • B. In direct ratio of their ratings
  • C. In inverse ratio of their ratings
  • D. Purely reactive

Answer: B. In direct ratio of their ratings

Explanation: For parallel transformers to share load proportional to their ratings without circulating currents, their per-unit impedances on their own ratings must be equal (load shared in direct ratio of ratings).

Question 16

The high frequency hum in the transformers is mainly due to

  • A. Loose laminations
  • B. Magnetostriction
  • C. Impurity in oil
  • D. Weakness of tank wall

Answer: B. Magnetostriction

Explanation: Transformer hum is caused primarily by magnetostriction—the microscopic periodic change in physical dimensions of ferromagnetic core laminations under an alternating magnetic flux.

Question 17

A 400/200 volts transformer has pu impedance of 0.05. The HV side voltage required to circulate full load current during short circuit test is

  • A. 20 V
  • B. 40 V
  • C. 10 V
  • D. 5 V

Answer: A. 20 V

Explanation: Full-load impedance drop on the HV side = pu impedance × HV rated voltage = 0.05 × 400 V = 20 V.

Question 18

Non-loading heat run test on transformers is performed by means of

  • A. SC test
  • B. OC test
  • C. Core balance test
  • D. Sumpner’s test

Answer: D. Sumpner’s test

Explanation: Sumpner's (back-to-back) test allows two identical transformers to be tested at full load for temperature rise without drawing total load power from the mains.

Question 19

A three phase induction motor is driving full-load torque which is independent of speed. If the line voltage drops to 90% of the rated value, % increase in motor copper losses

  • A. 23%
  • B. –18%
  • C. 123%
  • D. None of these

Answer: A. 23%

Explanation: Torque T ∝ sV² is constant, so s ∝ 1/V². Motor current I ≈ sV/R2 ∝ 1/V. When voltage drops to 0.9 V, current rises to I/0.9 = 1.111 I, and copper losses (I²R) increase to (1/0.9)² = 1/0.81 = 1.2346 (+23.5% ≈ 23%).

Question 20

A synchronous generator is feeding power to infinite bus bars at unity power factor. Its excitation is now increased. It will feed

  • A. The same power but at a leading power factor
  • B. The same power but at a lagging power factor
  • C. More power at unity power factor
  • D. Less power at unity power factor

Answer: B. The same power but at a lagging power factor

Explanation: Increasing the excitation of an alternator connected to infinite bus increases its induced EMF E above bus voltage V, delivering reactive power to the bus and causing it to operate at a lagging power factor (overexcited).

Question 21

The steam input in to a turbogenerator connected to infinite bus is increased. Which of the events will take place?

  • A. The generator will feed more leading KVAR to bus bar and power angle will not change
  • B. The generator will feed more real power to bus bar and power angle will increase
  • C. The generator will feed more power to bus bar and power angle will decrease
  • D. The generator will feed more lagging KVAR to bus bar and power angle will not change

Answer: B. The generator will feed more real power to bus bar and power angle will increase

Explanation: Increasing steam input supplies more mechanical power (Pm), which increases the active electrical power output (Pe = (EV/X) sin δ) and increases the power/torque angle δ.

Question 22

In an ideal transformer, which of the following statement is correct?

  • A. no voltage drops in resistance or leakage reactance
  • B. mmf required to maintain main flux is small
  • C. no core loss
  • D. all the above are correct

Answer: D. all the above are correct

Explanation: An ideal transformer has zero winding resistance (no I²R loss), zero leakage flux (no leakage reactance drops), zero core losses (no hysteresis/eddy losses), and infinite permeability (negligible magnetizing mmf).

Question 23

The voltage applied to a transformer primary is increased keeping v/f fixed. How will core loss and magnetizing current change?

  • A. Core loss will increase and magnetizing current remain same
  • B. Core loss will remain same and magnetizing current will remain same
  • C. Core loss will decrease and magnetizing current will increase
  • D. Core loss will remain same and magnetizing current will decrease

Answer: A. Core loss will increase and magnetizing current remain same

Explanation: Keeping V/f constant keeps peak flux density Bm constant (since Bm ∝ V/f). Magnetizing current remains constant, while core loss increases due to higher frequency (Wh ∝ f, We ∝ f²).

Question 24

Frequencies in the UHF range normally propagate by means of

  • A. Ground waves
  • B. Sky waves
  • C. Surface waves
  • D. Space waves

Answer: D. Space waves

Explanation: UHF radio waves (300 MHz to 3 GHz) penetrate the ionosphere without reflection and propagate primarily via line-of-sight space waves (tropospheric/direct waves).

Question 25

Indicate the antenna that is not wideband

  • A. Discone
  • B. Folded dipole
  • C. Helical
  • D. Marconi

Answer: D. Marconi

Explanation: Discone, folded dipole, and helical antennas exhibit wide bandwidth characteristics, whereas a standard Marconi (quarter-wave monopole) antenna is resonant and narrow-band.

Question 26

The depth of penetration of a wave in a lossy dielectric increases with increasing

  • A. Conductivity
  • B. Permeability
  • C. Wavelength
  • D. Permittivity

Answer: C. Wavelength

Explanation: Skin depth (depth of penetration) δ = 1/√(πfμσ). Since f = c/λ, δ ∝ 1/√f ∝ √λ, so depth of penetration increases with wavelength (lower frequency).

Question 27

Copper behaves as a

  • A. Conductor always
  • B. Conductor or dielectric depending on field strength
  • C. Conductor or dielectric depending on frequency
  • D. Conductor or dielectric depending on the electric current density

Answer: C. Conductor or dielectric depending on frequency

Explanation: At low and RF frequencies, conduction current dominates (σ >> ωε), so copper acts as a good conductor; at optical and X-ray frequencies above the plasma frequency, displacement current dominates and it behaves as a dielectric.

Question 28

Assuming constant transmission efficiency, if voltage is increased ‘n’ times, the size of the conductor would be

  • A. Reduced to 1/n^2 that of the original
  • B. Increased to n^2 that of the original
  • C. Reduced to 1/n that of the original
  • D. Increased to n times that of the original

Answer: A. Reduced to 1/n^2 that of the original

Explanation: For given power P, distance l, and percentage loss, conductor volume is inversely proportional to V² (Volume ∝ 1/V²). If voltage increases by a factor of n, conductor volume reduces to 1/n².

Question 29

Shunt conductance in overhead power transmission lines is primarily due to

  • A. Leakage over the insulators
  • B. Leakage over the conductors
  • C. Leakage over the poles
  • D. Leakage between ground and conductors

Answer: A. Leakage over the insulators

Explanation: Shunt conductance G represents the real leakage current flowing across the surface of overhead line insulators to the supporting towers and ground.

Question 30

The dielectric strength of SF6 gas (used in circuit breakers) is approximately

  • A. Same as that of air
  • B. 2 to 3 times more than air
  • C. 10 to 20 times more than air
  • D. 2 to 3 times less than air

Answer: B. 2 to 3 times more than air

Explanation: Sulphur hexafluoride (SF6) is an electronegative gas whose dielectric breakdown strength is roughly 2.5 to 3 times that of air at atmospheric pressure.

Question 31

Ferranti effect states that under certain conditions, the sending end voltage is

  • A. Less than receiving end voltage
  • B. Greater than receiving end voltage
  • C. Equal to receiving end voltage
  • D. Not having any impact on the receiving end voltage

Answer: A. Less than receiving end voltage

Explanation: Ferranti effect occurs on lightly loaded or open-circuited long transmission lines where line charging current through line inductance causes receiving end voltage VR to exceed sending end voltage VS (i.e. VS < VR).

Question 32

The equal area criterion of stability is applicable to

  • A. Two machine system and infinite bus bars
  • B. One machine system and infinite bus bars
  • C. Multi-machine system only
  • D. None of the above

Answer: B. One machine system and infinite bus bars

Explanation: Equal area criterion is a graphical method based on the swing equation, applicable strictly to a single machine connected to an infinite bus (or a two-machine equivalent system).

Question 33

The power transmission capacity of the transmission line is

  • A. Inversely proportional to the square of the voltage
  • B. Proportional to the voltage
  • C. Inversely proportional to the voltage
  • D. Proportional to the square of the operating voltage

Answer: D. Proportional to the square of the operating voltage

Explanation: Maximum power transmission capacity Pmax = (VS·VR)/X. Since VS and VR are proportional to nominal voltage V, Pmax ∝ V² (proportional to the square of operating voltage).

Question 34

If the torque angle ‘delta’ increases indefinitely, the system indicates

  • A. Steady state stability
  • B. Permanent stability
  • C. Instability
  • D. None of the above

Answer: C. Instability

Explanation: Stable operation requires dPe/dδ > 0. If the power angle δ increases beyond 90° indefinitely, synchronizing torque vanishes and the system loses synchronism (instability).

Question 35

Resistance switching is normally employed in

  • A. All breakers
  • B. Bulk oil breaker
  • C. Minimum oil breaker
  • D. Air-blast circuit breaker

Answer: D. Air-blast circuit breaker

Explanation: Resistance switching is universally employed in air-blast circuit breakers to damp transient recovery voltage (TRV) oscillations and suppress current chopping.

Question 36

Series capacitors are used to

  • A. Improve line frequency and eliminate harmonics
  • B. Compensate for line inductive reactance
  • C. Neutralise line capacitive reactance
  • D. None of the above

Answer: B. Compensate for line inductive reactance

Explanation: Series capacitors inserted directly in the line cancel part of the inductive reactance (Xnet = XL − Xc), reducing line impedance, enhancing power transfer capability, and improving voltage regulation.

Question 37

Over fluxing protection is normally recommended for

  • A. Generator transformers in power stations
  • B. Auto-transformers in power stations
  • C. Station transformers in power stations
  • D. Distribution transformers

Answer: A. Generator transformers in power stations

Explanation: Generator step-up (GSU) transformers in generating stations are vulnerable to overfluxing (V/f ratio exceeding limits) during generator startup, shutdown, or load rejection.

Question 38

In general AC distribution systems, arc interruption in vacuum circuit breakers are designed to function in a time period of

  • A. One cycle
  • B. Two to three cycles
  • C. Within ten cycles
  • D. None of the above

Answer: A. One cycle

Explanation: In vacuum circuit breakers, the arc diffuses rapidly into the high-dielectric vacuum and is cleanly extinguished at the very first natural current zero (within one cycle).

Question 39

Systems for Protection from negative sequence current is provided normally for

  • A. Transformers
  • B. Generators
  • C. Transmission lines
  • D. Motors

Answer: B. Generators

Explanation: Negative-sequence currents produce a reverse-rotating magnetic field at twice synchronous speed relative to the rotor, inducing double-frequency rotor eddy currents and severe overheating in synchronous generators.

Question 40

Bundled conductors are mainly used in high voltage overhead transmission lines to

  • A. Reduce line loss
  • B. Reduce harmonics
  • C. Reduce corona
  • D. Increase strength

Answer: C. Reduce corona

Explanation: Bundling conductors increases the effective conductor radius (GMR), lowering surface electrical field gradient, which significantly reduces corona loss and audible/radio interference.

Question 41

Surge impedance of overhead transmission line is normally in the order of

  • A. 1 – 5 ohms
  • B. 20 – 30 ohms
  • C. 300 – 500 ohms
  • D. 300000 – 500000 ohms

Answer: C. 300 – 500 ohms

Explanation: Surge impedance Zs = √(L/C) is typically 400 Ω (range 300–500 Ω) for overhead transmission lines, compared to 30–50 Ω for underground cables.

Question 42

The bode diagram approach is applied to

  • A. Non-minimum phase network
  • B. Minimum phase network
  • C. Any network of a control system
  • D. None of the above

Answer: B. Minimum phase network

Explanation: Bode diagram analysis directly relates magnitude and phase uniquely only for minimum-phase systems (all poles and zeros in the left half s-plane).

Question 43

Which of the following methods is the strongest tool to determine the stability and the transient response of the system?

  • A. Routh-Hurwitz criterion
  • B. Bode plot
  • C. Nyquist plot
  • D. Root locus

Answer: D. Root locus

Explanation: Root locus traces the exact trajectories of closed-loop poles in the s-plane as gain varies, providing complete information on both absolute/relative stability and transient response (damping ratio, natural frequency).

Question 44

If the gain of a critically damped system is increased, it will become

  • A. Under damped system
  • B. Over damped system
  • C. Oscillatory system
  • D. Critically damped system

Answer: A. Under damped system

Explanation: For a standard second-order system, increasing forward-path loop gain increases the natural frequency ωn without increasing the damping factor, reducing the damping ratio ζ below 1 (underdamped).

Question 45

The frequency domain and time domain are related through

  • A. Laplace transform
  • B. Gauss elimination
  • C. Both (a) and (b)
  • D. None of the above

Answer: A. Laplace transform

Explanation: The Laplace transform (and Fourier transform) provides the mathematical mapping converting time-domain differential equations into algebraic frequency-domain transfer functions.

Question 46

A system with characteristic equation s^4 + 2s^3 + 11s^2 + 18s + 18 = 0 will have closed loop poles such that

  • A. All poles lie in the left half of the s-plane
  • B. All poles lie in the right half of the s-plane
  • C. Two poles lie symmetrically on the imaginary axis of the s-plane.
  • D. No pole lies on the imaginary axis of the s-plane.

Answer: C. Two poles lie symmetrically on the imaginary axis of the s-plane.

Explanation: Routh array: s⁴: 1, 11, 18; s³: 2, 18; s²: 2, 18; s¹: row of zeros! Auxiliary polynomial A(s) = 2s² + 18 = 0 gives s = ±j3, so two poles lie symmetrically on the imaginary axis.

Question 47

If the gain of an open loop system is doubled, the gain margin

  • A. Is not affected
  • B. Gets double
  • C. Becomes half
  • D. Becomes one-fourth

Answer: C. Becomes half

Explanation: Gain margin GM = 1/|G(jωpc)|. If open-loop gain is doubled, |G(jωpc)| doubles, so the gain margin becomes half.

Question 48

An all pass network imparts only

  • A. Negative phase to the input
  • B. Positive phase to the input
  • C. +/–90 degree phase shift to the input
  • D. +/–180 degree phase shift to the input

Answer: A. Negative phase to the input

Explanation: An all-pass filter has constant unity gain (|H(jω)| = 1) across all frequencies and introduces pure negative phase lag (delay) to the input signal.

Question 49

An ON-OFF controller is

  • A. P controller
  • B. Integral controller
  • C. Non-linear controller
  • D. PID controller

Answer: C. Non-linear controller

Explanation: An ON-OFF (two-position) controller is inherently non-linear due to its discontinuous switching characteristic and hysteresis/deadband.

Question 50

The transfer function of a phase lead controller is (1 + 3Ts) / (1 + Ts). The maximum value of phase provided by this controller is

  • A. 90
  • B. 60
  • C. 45
  • D. 30

Answer: D. 30

Explanation: Phase lead transfer function G(s) = (1 + 3Ts)/(1 + Ts) has α = 1/3. Maximum phase lead φm = arcsin((1 − α)/(1 + α)) = arcsin((2/3)/(4/3)) = arcsin(0.5) = 30°.

Question 51

The thermal time constant is the time

  • A. To reach the final steady temperature if the initial rate of increase of temperature were maintained constant
  • B. To reach 63% of final steady temperature
  • C. To reach 66.66% of final steady temperature
  • D. To reach half of the final steady temperature

Answer: A. To reach the final steady temperature if the initial rate of increase of temperature were maintained constant

Explanation: Thermal time constant τ = H/A is classically defined as the time required to reach final steady-state temperature if the initial rate of temperature rise were maintained constant (also the time to reach 63.2% of steady temperature rise).

Question 52

Which of the following circuit will have no transients?

  • A. Pure resistive circuit
  • B. L-C Circuit
  • C. R-L-C Circuit
  • D. R-L Circuit

Answer: A. Pure resistive circuit

Explanation: Transients arise from energy storage in magnetic (inductor L) or electric (capacitor C) fields. A purely resistive circuit has no energy storage and responds instantaneously with zero transients.

Question 53

A conductor of length 100 cm moves right angles to a magnetic field of flux density of 2 wb/sq.m. with the velocity of 25 m/second. The induced emf in the conductor will be

  • A. 25 volts
  • B. 50 volts
  • C. 75 volts
  • D. 100 volts

Answer: B. 50 volts

Explanation: Induced EMF e = B·l·v·sin θ = 2 Wb/m² × 1.0 m × 25 m/s × sin 90° = 50 V.

Question 54

Which of the following devices are required to measure three phase balanced power?

  • A. One watt meter
  • B. One watt meter and one voltage transformer of 1 : 1 ratio
  • C. One watt meter and two voltmeters
  • D. None of the above

Answer: A. One watt meter

Explanation: For a balanced 3-phase load, total power can be measured using a single wattmeter by connecting its current coil in one line and creating a star/artificial neutral connection (Ptotal = 3·W).

Question 55

The sensitivity of an instrument is

  • A. The smallest increment in the input that can be detected with certainty
  • B. The largest input change to which the instrument fails to respond
  • C. Ratio of the change in the magnitude of the output to the corresponding change in the magnitude of the input
  • D. Closeness of the output values for repeated application of a constant input

Answer: C. Ratio of the change in the magnitude of the output to the corresponding change in the magnitude of the input

Explanation: Static sensitivity is defined as the ratio of the incremental change in instrument output magnitude (deflection) to the corresponding incremental change in input measured quantity.

Question 56

Potentiometer sensitivity can be increased by

  • A. Decreasing current in the potentiometer wire
  • B. Increasing the length of the potentiometer wire
  • C. Decreasing the length of the potentiometer wire
  • D. Replacing the cell by a regulated power supply

Answer: B. Increasing the length of the potentiometer wire

Explanation: Potentiometer sensitivity S = 1/k where potential gradient k = V/L. Increasing slide wire length L decreases the voltage gradient per unit length, allowing finer voltage resolution and higher sensitivity.

Question 57

Low resistance is measured with

  • A. De Sauty’s bridge
  • B. Maxwell’s bridge
  • C. Kelvin’s double bridge
  • D. Wien bridge

Answer: C. Kelvin’s double bridge

Explanation: Kelvin's double bridge eliminates contact and lead wire resistance errors, making it the standard precision instrument for measuring low resistances (< 1 Ω).

Question 58

Which bridge is used to determine frequency?

  • A. Anderson bridge
  • B. De Sautys bridge
  • C. Wien bridge
  • D. Campell’s bridge

Answer: C. Wien bridge

Explanation: Wien bridge is a frequency-selective AC bridge widely used for audio frequency measurement (f = 1/(2πRC)) and harmonic distortion analyzers.

Question 59

The core of a moving iron instrument is made up of permalloy to

  • A. Increase sensitivity
  • B. Reduce temperature effect
  • C. Reduce effect of stray magnetic field
  • D. Reduce the size of the instrument

Answer: C. Reduce effect of stray magnetic field

Explanation: Permalloy (high nickel-iron alloy) has extremely high magnetic permeability and negligible hysteresis loss, shielding moving-iron vanes from stray magnetic fields and minimizing hysteresis errors.

Question 60

Accuracy is defined as

  • A. The measure of consistency of the readings
  • B. Closeness with which an instrument reading approaches the true value of the quantity being measured
  • C. The smallest measurable input change
  • D. The ratio of the input to output

Answer: B. Closeness with which an instrument reading approaches the true value of the quantity being measured

Explanation: Accuracy denotes the degree of closeness between the measured instrument reading and the true accepted value of the quantity being measured.

Question 61

If three amplifiers having the same bandwidth are cascaded, the bandwidth of the resulting amplifier will be

  • A. Better than that of each stage
  • B. Worse than that of each stage
  • C. Same as that of each stage
  • D. None of the above

Answer: B. Worse than that of each stage

Explanation: Cascading n identical non-interacting amplifier stages reduces overall bandwidth: BWcascade = BWstage × √(2^(1/n) − 1). For n = 3, BWcascade ≈ 0.51 BWstage (worse than each stage).

Question 62

An element is said to have negative resistance when

  • A. The element has negative temperature coefficient
  • B. The current / voltage curve has negative slope
  • C. The element has negative specific resistance
  • D. The current / voltage curve has a positive slope

Answer: B. The current / voltage curve has negative slope

Explanation: Dynamic negative resistance is characterized by a region in the I-V curve where incremental resistance dV/dI < 0 (negative slope), as seen in tunnel diodes.

Question 63

The operational amplifiers are seldom used for differentiation because

  • A. Of the problem of drift with differentiating circuits
  • B. Because of the poor efficiency
  • C. Because of the complex circuitry requirements
  • D. The noises are amplified and this can be significant in the output.

Answer: D. The noises are amplified and this can be significant in the output.

Explanation: A differentiator has gain magnitude |H(jω)| = ωRC proportional to frequency, which excessively amplifies high-frequency noise and tends toward instability.

Question 64

Which of the following multivibrator is called the flip flop?

  • A. Astable multivibrator
  • B. Monostable multivibrator
  • C. Bistable multivibrator
  • D. Both (b) and (c)

Answer: C. Bistable multivibrator

Explanation: A bistable multivibrator has two stable states and requires an external trigger to switch between them, which is the operational definition of a digital flip-flop.

Question 65

The amount of feedback applied to an amplifier reduces the gain by a factor of 10. The bandwidth

  • A. Decreases by factor of 10
  • B. Increases by a factor of 10
  • C. Remains the same
  • D. None of the above

Answer: B. Increases by a factor of 10

Explanation: Negative feedback preserves the gain-bandwidth product (GBW = Af·BWf = A·BW). If closed-loop gain Af decreases by a factor of 10, the bandwidth increases by a factor of 10.

Question 66

In a negative feedback amplifier, the output impedance is decreased

  • A. If the signal sampled is a voltage
  • B. If the signal sampled is a current
  • C. If the feedback signal is a voltage
  • D. If the feedback signal is a current

Answer: A. If the signal sampled is a voltage

Explanation: Voltage sampling (shunt connection at output) stabilizes output voltage and reduces closed-loop output impedance by (1 + Aβ), whereas current sampling increases it.

Question 67

The ROM consists of

  • A. A decoder followed by an encoder
  • B. An encoder followed by a decoder
  • C. A multiplexer followed by a decoder
  • D. A multivibrator

Answer: A. A decoder followed by an encoder

Explanation: A Read-Only Memory (ROM) architecture consists of an input decoder (generating all 2^n minterms) followed by a programmable/fixed OR encoder array.

Question 68

An ideal rectifier should have transformer utilization factor (TUF) of 1. If the actual TUF is 3.5, it shows that

  • A. Diode is under-loaded
  • B. The transformer must be 3.5 times larger
  • C. The transformer should be only 1/3.5 times the ideal size
  • D. The ripple factor is low

Answer: B. The transformer must be 3.5 times larger

Explanation: TUF = Pdc / (Transformer VA rating). A lower TUF means a larger transformer is required for the same DC output; the transformer must be oversized proportionally.

Question 69

A power MOSFET is a

  • A. Voltage controlled device
  • B. Current controlled device
  • C. Frequency controlled device
  • D. None of the above

Answer: A. Voltage controlled device

Explanation: Power MOSFETs are unipolar, voltage-controlled devices where drain current is controlled by the electric field generated by gate-to-source voltage (Vgs).

Question 70

When transistors are used in series or parallel, a snubber circuit is used to

  • A. Control the current
  • B. Control the voltage
  • C. Limit di/dt
  • D. All of these

Answer: D. All of these

Explanation: Snubber networks (R-C-diode) suppress transient overvoltage spikes, limit dv/dt and di/dt during switching, and assist static and dynamic voltage equalization across series/parallel devices.

Question 71

lim (x -> infinity) of ((x + sin x)/x) equals to

  • A. –∞
  • B. 0
  • C. 1
  • D. ∞

Answer: C. 1

Explanation: lim(x→∞) (x + sin x)/x = lim(x→∞) [1 + (sin x)/x]. Since −1 ≤ sin x ≤ 1, (sin x)/x → 0 as x → ∞, giving 1 + 0 = 1.

Question 72

A fair (unbiased) coin was tossed four times in succession and resulted in the following outcomes: (i) Head (ii) Head (iii) Head (iv) Head. The probability of getting a ‘Tail’ when the coin is tossed again is

  • A. 0
  • B. 1/2
  • C. 4/5
  • D. 1/5

Answer: B. 1/2

Explanation: Each toss of a fair coin is an independent Bernoulli trial. Previous outcomes have no memory effect; the probability of getting a Tail on the next toss is strictly 1/2.

Question 73

What are the eigen values of the following 2 × 2 matrix [[2, -1], [-4, 5]] (rows: (2, -1) and (-4, 5))?

  • A. –1 and 1
  • B. 1 and 6
  • C. 2 and 5
  • D. 4 and –1

Answer: B. 1 and 6

Explanation: Characteristic equation det(A − λI) = (2 − λ)(5 − λ) − (−1)(−4) = λ² − 7λ + 10 − 4 = λ² − 7λ + 6 = (λ − 1)(λ − 6) = 0, so eigenvalues are 1 and 6.

Question 74

The double integral from 0 to π/2 and 0 to π/2 of sin(x + y) dx dy is

  • A. 0
  • B. π
  • C. π/2
  • D. 2

Answer: D. 2

Explanation: ∫₀^(π/2) ∫₀^(π/2) sin(x + y) dx dy = ∫₀^(π/2) [−cos(x + y)]₀^(π/2) dy = ∫₀^(π/2) [cos y + sin y] dy = [sin y − cos y]₀^(π/2) = (1 − 0) − (0 − 1) = 2.

Question 75

In the Taylor series expansion of e^x + sin x about the point x = π, the coefficient

  • A. e^π
  • B. 0.5 e^π
  • C. e^(π+1)
  • D. e^(π-1)

Answer: B. 0.5 e^π

Explanation: The Taylor series coefficient for (x − π)² is f''(π)/2!. f'(x) = e^x + cos x, f''(x) = e^x − sin x. At x = π, f''(π) = e^π − sin π = e^π. Thus, coefficient = e^π/2! = 0.5 e^π.

Question 76

A deck of five cards (each carrying a distinct number from 1 to 5) is shuffled thoroughly. Two cards are then removed from the deck, one at a time. What is the probability that the two cards are selected with the number of the first card being one higher than the number on the second card?

  • A. 1/5
  • B. 4/25
  • C. 1/4
  • D. 2/5

Answer: A. 1/5

Explanation: Total ordered pairs of cards selected without replacement from {1,2,3,4,5} is 5 × 4 = 20. Favorable pairs (first = second + 1) are (2,1), (3,2), (4,3), (5,4), giving 4 pairs. Probability = 4/20 = 1/5.

Question 77

Using trapezoidal rule for the table given below, the integral from 4 to 5.2 of ln x dx will be. [Table: x: 4, 4.2, 4.4, 4.6, 4.8, 5.0, 5.2; Ln x: 1.39, 1.44, 1.48, 1.53, 1.57, 1.61, 1.65]

  • A. 1.8277
  • B. 1.9284
  • C. 1.6424
  • D. 0.98795

Answer: A. 1.8277

Explanation: Trapezoidal rule with step h = 0.2: I ≈ (h/2)·[y0 + yn + 2·Σ y_mid] = 0.1·[1.39 + 1.65 + 2·(1.44 + 1.48 + 1.53 + 1.57 + 1.61)] = 0.1·[3.04 + 15.26] = 0.1 × 18.30 = 1.83 (closest to 1.8277).

Question 78

Find the z transform of (n + 1)^2

  • A. z^2(2z + 1)/(z - 1)^3
  • B. (2z + 1)/(z - 1)^3
  • C. (2 + z)/(z - 1)^2
  • D. (3z + 2)/(z - 1)

Answer: A. z^2(2z + 1)/(z - 1)^3

Explanation: Z{(n + 1)²} = Z{n² + 2n + 1}. With Z{1} = z/(z−1), Z{n} = z/(z−1)², Z{n²} = z(z+1)/(z−1)³, combining yields z²(2z + 1)/(z − 1)³.

Question 79

Consider the following system of equations in three real variables x1, x2 and x3: 2x1 - x2 + 3x3 = 1; 3x1 - 2x2 + 5x3 = 2; -x1 - 4x2 + x3 = 3. The system of equations has :

  • A. No solutions
  • B. A unique solution
  • C. More than one but a finite number of solutions
  • D. An infinite number of solutions

Answer: B. A unique solution

Explanation: Coefficient matrix determinant det = 2(−2·1 − 5·(−4)) − (−1)(3·1 − 5·(−1)) + 3(3·(−4) − (−2)(−1)) = 2(18) + 1(8) + 3(−14) = 36 + 8 − 42 = 2 ≠ 0. Since det ≠ 0, the linear system has a unique solution.

Question 80

Which of the following functions would have only odd powers of x in its Taylor series expansion about the point x = 0?

  • A. sin(x^3)
  • B. sin(x^2)
  • C. cos(x^3)
  • D. cos(x^2)

Answer: A. sin(x^3)

Explanation: sin(x³) = x³ − x⁹/6 + … contains only odd powers; the others contain even powers.