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Past Questions — 2015
In a communication system, noise is most likely to affect the signal
A)
at the transmitter
B)
in the channel
C)
at the information source
D)
at the destination
In a communication system, noise is mainly introduced during transmission through the channel, where the signal is exposed to interference, attenuation, and external disturbances. The transmitter and information source generate the signal, while the destination receives it; noise is most likely to corrupt the signal in the channel.
The conducting thyristor is turned off when load current flowing through a thyristor becomes zero due to the nature of load circuit parameters in
A)
Load commutation
B)
Current commutation
C)
Voltage commutation
D)
Source commutation
In load commutation, the load circuit parameters (RLC nature of the load) cause the current through the conducting thyristor to fall to zero naturally, turning it off. This is also called self-commutation.
Why others are incorrect:
- Current commutation: uses an auxiliary current to force the thyristor current to zero.
- Voltage commutation: applies a reverse voltage to turn off the thyristor.
- Source commutation: turn-off is achieved by the AC source current naturally going to zero, not by load parameters.
Which of these is not a type of chopper circuit?
A)
Type C chopper
B)
Type A chopper
C)
Type E chopper
D)
Type F chopper
Chopper circuits are commonly classified as Type A, Type B, Type C, Type D, and Type E. Therefore, Type F chopper is not a standard type of chopper circuit. Hence, the correct answer is Type F chopper.
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.
In an SCR, when the anode is positive with respect to the cathode, with gate circuit opened, small leakage current flows. This mode of operation is called
A)
Reverse blocking mode
B)
Forward blocking mode
C)
Reverse conduction mode
D)
Forward conduction mode
When the anode is positive with respect to the cathode and the gate is open, the SCR is in the forward-biased state but not yet triggered. In this condition, only a small leakage current flows, so it is called the forward blocking mode. Reverse blocking mode occurs when the anode is negative with respect to the cathode.
A network contains linear resistors and ideal voltage sources. If the values of all the resistors are doubled, then the voltage across each resistor is
A)
halved
B)
doubled
C)
increased by four times
D)
not changed
In a network containing only linear resistors and ideal voltage sources, if all resistor values are doubled, the circuit currents are reduced accordingly, but the voltage division pattern remains the same. Since each resistor voltage is V = IR, and both I and R change in opposite ways, the product stays unchanged. Therefore, the voltage across each resistor does not change. Hence, the correct option is (d) not changed.
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.
In an inverter, the load current waveform is identical to the load voltage waveform in a/an___load.
A)
R
B)
RL
C)
RLC overdamped
D)
RLC underdamped
In a purely resistive load, current is directly proportional to voltage at every instant (Ohm’s law: i = v/R). Therefore, the load current waveform has the same shape as the load voltage waveform. In RL or RLC loads, inductance/capacitance causes phase shift and waveform distortion, so the current is not identical to the voltage waveform.
The hysteresis and eddy current loss resulting from alternations of magnetic flux in the core of a transformer is called
A)
Copper loss
B)
Load loss
C)
Core loss
D)
Dielectric loss
In a transformer, the alternating magnetic flux in the iron core causes two main losses: hysteresis loss and eddy current loss. Together, these are called core loss or iron loss. Copper loss is due to resistance of the windings, load loss is a broader term related to load-dependent losses, and dielectric loss occurs in insulating materials.
From the viewpoint of connections of semiconductor devices, the one which is not an inverter is
A)
Bridge Inverter
B)
Series Inverter
C)
Parallel Inverter
D)
Branch Inverter
In power electronics, common inverter classifications based on circuit connection include bridge inverter, series inverter, and parallel inverter. 'Branch inverter' is not a standard inverter type in this classification. Therefore, the option that is not an inverter is Branch Inverter.
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.
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 is decreasing by 2: 19, 19, 17, 15, so the next difference should be 13. Therefore, 50 − 13 = 37. Hence, the correct answer is 37.
From what location are the 1st computer instructions available on boot up?
A)
ROM BIOS
B)
CPU
C)
boot.ini
D)
CONFIG.SYS
On boot up, the first instructions executed by the computer are stored in the ROM BIOS. The BIOS performs the Power-On Self Test (POST) and then starts the boot process. The CPU only executes instructions; it does not store the initial boot instructions. boot.ini and CONFIG.SYS are operating system-related files loaded later in the startup process, not the first source of instructions.
What is the electrical path that connects the CPU, memory, and the other hardware devices on the motherboard?
A)
PCI bus
B)
Address bus
C)
Data bus
D)
AGP bus
The data bus is the electrical pathway used to transfer data between the CPU, memory, and other hardware devices on the motherboard. The address bus carries memory addresses, not the actual data. PCI bus and AGP bus are specific expansion buses for certain devices, not the general path connecting CPU, memory, and peripherals.
In a superheterodyne receiver
A)
the IF stage has better selectivity than RF stage
B)
the RF stage has better selectivity than IF stage
C)
the RF stage has same selectivity than IF stage
D)
None of these
In a superheterodyne receiver, the incoming RF signal is converted to a fixed intermediate frequency (IF). Since the IF is fixed, the IF amplifier can be designed with high-gain, narrow-band tuned circuits, giving it better selectivity. The RF stage mainly provides initial tuning and image-frequency rejection, but its selectivity is comparatively lower. Therefore, the IF stage has better selectivity than the RF stage.
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).
Single phase full-wave midpoint converter is also called
A)
F-2
B)
M-2
C)
A-2
D)
None of these
A single-phase full-wave midpoint converter uses two thyristors and a center-tapped transformer secondary, so it is commonly called an M-2 converter. In converter notation, M denotes midpoint configuration and 2 denotes two devices. F-2 refers to a full-controlled bridge type, not midpoint. A-2 is not the standard name for this circuit.
A freewheeling diode is also called
A)
Commutating diode
B)
Terminal diode
C)
Vaccum diode
D)
Zener diode
A freewheeling diode provides an alternate path for inductive load current when the main switch turns OFF, helping the current to continue flowing smoothly. Because it assists in commutation of current, it is also called a commutating diode. The other options are incorrect: a terminal diode is not the standard term here, a vacuum diode is an electron tube, and a Zener diode is used for voltage regulation.
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.
The rate at which information can be carried through a communication channel depends on
A)
Carrier frequency
B)
Bandwidth
C)
Transmission loss
D)
Transmitted power
The rate at which information can be carried through a communication channel is primarily determined by the channel bandwidth. By Shannon’s communication principle, a wider bandwidth allows a higher data rate. Carrier frequency only sets the operating range, transmission loss affects signal strength, and transmitted power affects reliability/SNR, but the fundamental capacity depends on bandwidth.
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.
7, 15, 29, 59, 117, ?
A)
232
B)
233
C)
235
D)
236
The pattern is: multiply by 2 and subtract 1.
7 → 15 = 7×2 + 1
15 → 29 = 15×2 - 1
29 → 59 = 29×2 + 1
59 → 117 = 59×2 - 1
So the next term is 117×2 - 1 = 233.
Therefore, the correct answer is 233.
Which type of transmission do modems use?
A)
Synchronous
B)
Asynchronous
C)
Timeinterval
D)
Bank
Modems commonly use asynchronous transmission in basic serial communication, where data is sent one character at a time with start and stop bits. This is the standard answer in such exam questions. Synchronous transmission is used in systems where data is sent in continuous blocks with a shared clock, which is not the usual modem transmission mode asked here. 'Timeinterval' and 'Bank' are not valid transmission types.
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.
A transducer’s function is to
A)
Transmit electrical energy
B)
Convert energy
C)
Produce mechanical energy
D)
Prevent current flow
A transducer converts one form of energy into another form, usually converting a physical quantity like temperature, pressure, displacement, etc. into an electrical signal. Hence, the correct function is to convert energy. The other options are incorrect because a transducer does not transmit electrical energy, produce mechanical energy specifically, or prevent current flow.