← Junior Engineer
Past Questions
The Superposition Theorem is not applicable to networks containing
A)
nonlinear elements
B)
dependent voltage sources
C)
dependent current sources
D)
transformers
The Superposition Theorem is valid only for linear networks. It can be applied even when the circuit contains independent or dependent sources, and transformers are also linear elements. However, it is not applicable to networks containing nonlinear elements such as diodes, transistors operating nonlinearly, or saturable devices, because the response is not directly proportional to the excitation.
In a CRO which of the following is not a part of electron gun?
A)
Cathode
B)
Grid
C)
Accelerating anode
D)
X-Y plates
In a CRO, the electron gun consists of the cathode, control grid, and accelerating/focusing anodes. These parts generate, control, and accelerate the electron beam. The X-Y plates are not part of the electron gun; they are deflection plates used to move the beam on the screen horizontally and vertically.
HVDC is less reliable and has lower availability than alternating current (AC) systems, mainly due to
A)
More losses
B)
Extra equipments required
C)
Noise
D)
None of these
HVDC systems are considered less reliable and have lower availability than AC systems mainly because they need additional converter stations and associated control/protection equipment at both ends. These extra equipments increase complexity and the chance of failure. The issue is not primarily more transmission losses or noise. Therefore, the correct answer is 'Extra equipments required'.
An induction motor always runs with a _______ power factor.
A)
Leading
B)
Lagging
C)
Unity
D)
Zero
An induction motor needs magnetizing current to establish the rotating magnetic field in the stator. This magnetizing component is inductive in nature, so the current drawn by the motor lags behind the supply voltage. Therefore, an induction motor always runs with a lagging power factor. Leading is incorrect, unity is not possible in normal operation, and zero power factor is not the case.
Which test determines the series parameters of a transformer?
A)
Open circuit test
B)
Short circuit test
C)
Polarity test
D)
Back to back test
The short circuit test is used to determine the series parameters of a transformer, namely the equivalent resistance and leakage reactance referred to one side. In this test, a low voltage is applied to circulate rated current, so the shunt branch is neglected and only the series branch is obtained. The open circuit test determines the shunt parameters (core loss resistance and magnetizing reactance), not the series parameters. Polarity test checks the relative polarity of windings, and back-to-back test is used mainly for efficiency and loss determination of two identical transformers.
The snubber circuit is used in a thyristor circuit for
A)
di/dt protection
B)
dv/dt protection
C)
phase shifting
D)
prevention of local hot spots
A snubber circuit in a thyristor circuit is mainly used to protect the thyristor from a high rate of rise of voltage across it, i.e., dv/dt. If dv/dt is too high, the thyristor may turn on unintentionally. A snubber also helps in limiting transient voltages.
Why others are incorrect:
- (a) di/dt protection is mainly related to limiting the rate of rise of current, usually handled by series inductance.
- (c) phase shifting is not the function of a snubber circuit.
- (d) prevention of local hot spots is not the primary purpose of a snubber in thyristor circuits.
Which of these is not a basic component of a numerical control system?
A)
Input medium
B)
Machine Control Unit (MCU)
C)
Mechanical Control Unit
D)
Machine Tool
A numerical control (NC) system has three basic components: the input medium, the Machine Control Unit (MCU), and the machine tool. The input medium carries the program instructions, the MCU interprets them, and the machine tool performs the actual operation. 'Mechanical Control Unit' is not a standard basic component of an NC system.
ARM has 37 registers in total, all of which are _______ bits long.
A)
8
B)
16
C)
32
D)
64
ARM architecture has 37 registers in total across its different modes, and each register is 32 bits wide. Therefore, the correct answer is 32 bits. The other options are incorrect because ARM registers are not 8, 16, or 64 bits long in this context.
The smallest increment of positioning that is possible in a Numerical Control System is called
A)
Resolution
B)
Repeatability
C)
Accuracy
D)
Integration
In a Numerical Control (NC) system, the smallest possible increment of movement or positioning is called the **resolution**. It indicates the minimum step size the system can command.
- **Resolution**: smallest increment of positioning — correct.
- **Repeatability**: ability to return to the same position consistently.
- **Accuracy**: closeness of the actual position to the desired position.
- **Integration**: not a standard term for positioning increment in NC systems.
Therefore, the correct answer is **Resolution**.
An LVDT is used to measure displacement. The LVDT feeds a Voltmeter of 0-5 V range through a 250 gain amplifier. For a displacement 0.5 mm the output of LVDT is 2 mV. The sensitivity of instrument is
A)
1V/mm
B)
0.1 V/mm
C)
5V/énm
D)
0.5 V/mm
Given LVDT output for 0.5 mm displacement = 2 mV. With amplifier gain 250, voltmeter input/output becomes 2 mV × 250 = 500 mV = 0.5 V for 0.5 mm. Therefore sensitivity = output/displacement = 0.5 V / 0.5 mm = 1 V/mm. However, since the options include 0.5 V/mm and the usual interpretation in such questions is the amplified output corresponding to 1 mm, the correct calculated sensitivity from the given data is 1 V/mm. The closest intended option appears to be (a), but the data and options are inconsistent.
The value of current at resonance in a series RLC circuit is affected by the value of
A)
R
B)
L
C)
C
D)
All of these
In a series RLC circuit at resonance, the inductive and capacitive reactances cancel each other, so the impedance becomes minimum and equal to the resistance R only. Hence the resonant current is I = V/R, so it depends on R. L and C affect the resonant frequency, but not the current value at resonance directly.
The term thyristor denotes a family of semiconductor devices used for power control in system(s).
A)
only AC
B)
AC and DC
C)
only DC
D)
neither AC nor DC
A thyristor is a family of semiconductor power-control devices used in both AC and DC circuits. It is widely used for controlled rectification, AC voltage control, DC motor control, and other power electronic applications. Hence, the correct choice is AC and DC. The other options are incorrect because thyristors are not limited to only AC or only DC, and they are certainly used in power control systems.
When checking a good SCR or TRIAC with an ohmmeter it will
A)
Show high resistance in both directions
B)
Show low resistance with positive on anode and negative on cathode, and high resistance when reversed
C)
Show high resistance with negative on anode and positive on cathode, and low resistance when reversed
D)
Show low resistance in both directions
A good SCR or TRIAC should not conduct in either direction when tested with an ohmmeter in its normal, untriggered state. Therefore, it will indicate high resistance both ways. If it shows low resistance in either direction without triggering, the device is likely faulty.
Which power amplifier can deliver maximum load power?
A)
Class A
B)
Class AB
C)
Class B
D)
Class C
Among the given power amplifier classes, Class C has the highest efficiency and can deliver the maximum load power for a given supply, because the transistor conducts for less than 180° of the input cycle. Class A has the lowest efficiency, Class AB is better than Class A, and Class B is more efficient than Class A but still below Class C. Hence, Class C can deliver maximum load power.
CNC is an abbreviation for
A)
Computerised Numerically Contoured
B)
Computerised Numerically Controlled
C)
Centralised Numerically Controlled
D)
None of these
CNC stands for Computerised Numerically Controlled. It refers to machines controlled by a computer program for precise automated operation. Option (a) is incorrect because 'Contoured' is not part of the standard expansion. Option (c) is incorrect because CNC is not 'Centralised'. Option (d) is incorrect because the correct expansion is given in option (b).
In communication systems, the link between the Sender and the Receiver is called the
A)
Channel
B)
Way
C)
Message
D)
None of these
In a communication system, the sender transmits a message to the receiver through a medium called the channel. The channel is the physical link or path that carries the signal. 'Message' is the information being sent, not the link, and 'Way' is not a standard term in communication systems.
An amplifier has a large ac input signal. The clipping occurs on both the peaks. The output voltage will be nearly a
A)
Sine wave
B)
Square wave
C)
Triangular wave
D)
Sawtooth wave
When an amplifier is driven by a large AC input signal, the output can exceed the linear operating range and get clipped at both the positive and negative peaks. Symmetrical clipping on both peaks makes the waveform approach a square wave. A sine wave is the original undistorted shape, while triangular and sawtooth waves are not produced by simple peak clipping.
A thin strand of glass that transmits pulsating beams of light for transmission of data is called
A)
Fiber-optic cable
B)
Coaxial cable
C)
Twisted pair cable
D)
None of these
A thin strand of glass used to transmit data as pulses of light is a fiber-optic cable. It carries information through light signals, allowing high-speed and low-loss communication. Coaxial cable uses a copper conductor with shielding, and twisted pair cable uses pairs of insulated copper wires, so neither matches the description.
In an induction motor, the rotor field runs with respect to the stator at
A)
synchronous speed in the same direction as the stator field
B)
synchronous speed in the opposite direction as the stator field
C)
slip speed in the same direction as the stator field
D)
slip speed in the opposite direction as the stator field
In an induction motor, the stator produces a rotating magnetic field at synchronous speed. The rotor current is induced due to relative motion between the stator field and rotor, and the rotor magnetic field is produced by these rotor currents. This rotor field rotates with respect to the stator at synchronous speed in the same direction as the stator field. Relative to the rotor, however, it runs at slip speed. Hence, option (a) is correct. Options (c) and (d) describe motion relative to the rotor, not the stator.
A microcontroller based device with input/output circuitry that monitors the status of field connected inputs and controls the output actuators according to a user created logic program stored in a memory is called
A)
Programmable Logic Converter
B)
Programmable Logic Counter
C)
Arithmetic Logic Unit
D)
Control Unit
The description refers to a microcontroller-based industrial control device that reads inputs from field devices, executes a stored logic program, and drives outputs/actuators. This is the function of a PLC. Among the given options, the intended answer is (a) Programmable Logic Converter, though the standard full form is Programmable Logic Controller. The other options are incorrect: a Programmable Logic Counter is not a standard control device, an Arithmetic Logic Unit is only a CPU component, and a Control Unit is also a part of a processor, not a standalone field-control device.
Which SMPS configuration is used for high power applications (above 750 W)?
A)
Flyback converter
B)
Push-pull converter
C)
Half-bridge converter
D)
Full-bridge converter
In SMPS, the full-bridge converter is preferred for high-power applications because it can handle larger power levels efficiently and with better transformer utilization. Flyback converters are used for low-power applications, push-pull and half-bridge are used for medium power ranges, while full-bridge is typically used above about 750 W. Hence, the correct answer is Full-bridge converter.
Each network host is connected to a central hub with a point-to-point connection in a _______ topology.
A)
Bus
B)
Mesh
C)
Star
D)
Ring
In a star topology, every network host is connected directly to a central hub or switch using a separate point-to-point link. In a bus topology, all devices share one common backbone; in a mesh topology, devices are interconnected with multiple links; and in a ring topology, each device connects to two others in a closed loop.
No load current is the current
A)
which flows through the primary winding, when the secondary winding is open
B)
which flows through the secondary winding, when the primary winding is closed
C)
which flows through the secondary winding, when the primary winding is open
D)
which flows through the primary winding, when the secondary winding is closed
No-load current is the small current drawn by the primary of a transformer when the secondary is open-circuited. It is needed to establish the magnetic flux in the core and supply core losses. Hence, option (a) is correct. Options (b) and (c) are wrong because current does not flow in the secondary when it is open or when the primary is open. Option (d) is wrong because the primary current under no-load condition occurs when the secondary is open, not closed.
The energy radiated by the sun in bright sunny day is about
A)
2.5 kW/m²
B)
1.0 kW/m²
C)
500 W/m²
D)
200 W/m²
On a bright sunny day, the solar radiation received at the earth’s surface is approximately 1 kW/m² (about 1000 W/m²) under standard clear-sky conditions. This is the commonly accepted value used in solar engineering. The other options are either too high (2.5 kW/m²) or too low (500 W/m², 200 W/m²).
120, 101, 82, 65, 50, ?
A)
37
B)
40
C)
41
D)
42
Look at the differences between consecutive terms: 120→101 = -19, 101→82 = -19, 82→65 = -17, 65→50 = -15. The pattern of subtraction is decreasing by 2 each time after the first repeated difference: -19, -19, -17, -15, so the next difference should be -13. Therefore, 50 - 13 = 37. Hence, the correct answer is 37.