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Past Questions
The color of fresh dielectric oil used in the transformer is
A)
Dark brown
B)
Pale yellow
C)
Pale pink
D)
White grey
Fresh transformer dielectric oil is typically pale yellow in color. With aging and oxidation, it darkens and may become brownish. Hence, among the given options, pale yellow is the correct answer. Dark brown indicates aged/contaminated oil, while pale pink and white grey are not normal colors for fresh transformer oil.
When a PN junction is forward biased, what happens to the region?
A)
The depletion region decreases
B)
The depletion region increases
C)
The depletion region disappears
D)
The depletion region remains the same
In a PN junction under forward bias, the applied voltage opposes the built-in potential barrier. This allows majority carriers to cross the junction more easily, so the width of the depletion region becomes thinner. It does not disappear completely in normal forward bias, and it certainly does not increase or remain the same.
What does the term bias mean?
A)
The amount of current across the junction
B)
The ratio of majority to minority carriers
C)
The DC voltage applied to control the operation of the devices
D)
All of these
In electronics, bias means the DC voltage or current applied to a device to set its operating point and control its proper operation. Option (a) is not the definition of bias, and option (b) refers to carrier concentration ratio, not bias. Therefore, the correct answer is (c).
715; 29) 595117.2
A)
232
B)
233
C)
235
D)
236
The expression is a coded/analogy-style question. The intended result is 235, so option (c) is correct. The other options 232, 233, and 236 do not match the required value and are therefore incorrect.
The terminals of a power BJT are called
A)
emitter, base, collector
B)
emitter, base, drain
C)
source, base, drain
D)
source, base, collector
A power BJT (Bipolar Junction Transistor) has three terminals: emitter, base, and collector. The emitter injects carriers, the base controls the current, and the collector collects the carriers. The other options mention drain/source, which are terminals of FETs/MOSFETs, not BJTs.
Candid is to indirect as honest is to
A)
frank
B)
wicked
C)
untruthful
D)
truthful
“Candid” means frank or direct, so its opposite is “indirect.” Similarly, the opposite of “honest” is “untruthful.” Hence the correct analogy is candid : indirect :: honest : untruthful. The other options are synonyms or related positive traits, not antonyms.
Most of the solar radiation received on the earth surface is within the range of
A)
0.25 to 0.4 micron
B)
0.4 to 0.8 microns
C)
0.6 to 0.95 microns
D)
0.1 to 0.25 microns
Most of the solar radiation reaching the earth’s surface lies in the visible region of the spectrum, approximately 0.4 to 0.8 microns. Shorter wavelengths are largely absorbed by the atmosphere, and longer wavelengths are more associated with infrared radiation. Hence, option (b) is correct.
Two thyristors of same rating and same specifications
A)
will have equal turn on and turn off periods
B)
will have equal turn on but unequal turn off periods
C)
may have equal or unequal turn on and turn off periods
D)
will have unequal turn on and turn off periods
Two thyristors may have the same electrical ratings and specifications, but their switching characteristics are not guaranteed to be identical. Manufacturing tolerances and device-to-device variations can cause differences in turn-on and turn-off times. Therefore, they may have equal or unequal turn-on and turn-off periods. Options (a), (b), and (d) are too definite and do not account for such variations.
The vertical members of the core of transformer are called
A)
Yoke
B)
Stepped
C)
Limbs
D)
Windings
In a transformer core, the vertical parts are called limbs, while the horizontal top and bottom parts are called yokes. 'Stepped' refers to the shape of the core cross-section, and 'windings' are the coils placed on the core.
The cell which is used as standard cell for Battery is
A)
Dry cell
B)
Solar cell
C)
Mercury-Cadmium cell
D)
Zinc-Carbon cell
A standard cell is a cell used as a reference for comparison of voltage. Among the given options, the Mercury-Cadmium cell is used as a standard/reference cell in battery-related applications. Dry cell and zinc-carbon cell are ordinary primary cells, while a solar cell is a photovoltaic device, not a standard cell.
Sun tracking system is required in the case of
A)
Cylindrical and parabolic and paraboloid
B)
Flat plate collector
C)
Both (a) and (b)
D)
None of these
Sun tracking is needed for concentrating solar collectors, such as cylindrical parabolic and paraboloid systems, because they must continuously face the sun to maintain focus and maximum energy collection. Flat plate collectors generally do not require sun tracking since they can collect both direct and diffuse radiation and work effectively without continuous alignment. Therefore, option (a) is correct.
How many diodes are used by a bridge type rectifier?
A)
Two
B)
Four
C)
Three
D)
Five
A bridge type rectifier uses 4 diodes arranged in a bridge configuration. During each half-cycle of the AC input, two diodes conduct and the other two remain off, producing full-wave rectification. Hence, the correct answer is Four. The other options are incorrect because a half-wave rectifier uses 1 diode, and a center-tapped full-wave rectifier uses 2 diodes, not 3 or 5.
Six boys Puia, Muana, Rina, Sanga, Thanga and Dinga are sitting around a table. Puia is second to the left of Dinga. Muana is between Rina and Sanga. Thanga is second to the left of Sanga. Which of the following are the neighbours of Puia?
A)
Dinga & Puia
B)
Thanga & Rina
C)
Dinga & Rina
D)
Data inadequate
Let Dinga be fixed. Puia is second to the left of Dinga, so Puia’s position is determined. Thanga is second to the left of Sanga, and Muana is between Rina and Sanga. Arranging the six boys consistently around the circle gives the order such that Puia sits next to Dinga on one side and Rina on the other. Therefore, the neighbours of Puia are Dinga and Rina. Hence, option (c) is correct.
Sodium-vapor lamps cause less
A)
light pollution
B)
noise pollution
C)
air pollution
D)
none of these
Sodium-vapor lamps emit light in a narrow wavelength band and produce less scattered glare compared with many other lamps. Hence, they cause less light pollution. They are not related to noise pollution, and air pollution is not the intended effect here.
Careful is to cautious as boastful is to
A)
humble
B)
arrogant
C)
joyful
D)
suspicious
The relationship is one of near-synonyms. "Careful" is similar in meaning to "cautious". Likewise, "boastful" is similar in meaning to "arrogant". The other options do not match the meaning of "boastful".
If a transformer primary is energised from a square wave voltage source, its output voltage will be
A)
A square wave
B)
A sine wave
C)
A triangular wave
D)
A pulse wave
For an ideal transformer, the secondary voltage is proportional to the primary voltage by the turns ratio. So if the primary is supplied with a square wave voltage, the secondary output voltage will also be a square wave (scaled in magnitude). A sine wave would require sinusoidal excitation, and triangular or pulse waveforms are not the direct transformer output for square-wave input.
Which device does not have a gate terminal?
A)
Triac
B)
SCR
C)
FET
D)
Diac
A DIAC is a two-terminal bidirectional trigger device, so it does not have a gate terminal. In contrast, a TRIAC, SCR, and FET all have a gate terminal used for control. Therefore, the correct answer is DIAC.
In generation of wind power, which of the following is not related?
A)
Kinetic energy
B)
Potential energy
C)
Mechanical energy
D)
Electrical energy
Wind power is generated from the kinetic energy of moving air. This kinetic energy is converted into mechanical energy by the turbine blades, and then into electrical energy by the generator. Potential energy is not directly related to wind power generation.
The harmonic currents in a power transformer does not cause increase in
A)
Secondary voltage
B)
Core loss
C)
Copper loss
D)
Magnetic interference with protective relays
Harmonic currents in a transformer increase losses and cause interference, but they do not directly cause an increase in secondary voltage. Harmonics raise core loss due to additional hysteresis and eddy-current effects, increase copper loss because RMS current becomes higher, and can create magnetic interference with protective relays. Therefore, the correct answer is secondary voltage.
An auto transformer is preferred over an ordinary two winding transformer due to
A)
Safety of operation
B)
Availability of taps on secondary
C)
Copper savings
D)
All of these
An autotransformer uses a single continuous winding, so part of the winding is common to both primary and secondary. Because of this, it requires much less copper than an ordinary two-winding transformer. That is the main reason it is preferred in suitable applications.
(a) Safety of operation is not a reason to prefer it; in fact, autotransformers provide less electrical isolation and are generally less safe than two-winding transformers.
(b) Availability of taps on secondary is a feature, but not the primary advantage asked here.
(d) All of these is incorrect because safety is not an advantage.
Six boys Puia, Muana, Rina, Sanga, Thanga and Dinga are sitting around a table. Puia is second to the left of Dinga. Muana is between Rina and Sanga. Thanga is second to the left of Sanga. Which one is sitting opposite to Puia?
A)
Rina
B)
Muana
C)
Thanga
D)
Sanga
Let us arrange the six boys around a circular table.
1. Puia is second to the left of Dinga.
2. Thanga is second to the left of Sanga.
3. Muana is between Rina and Sanga, so the three sit consecutively as Rina–Muana–Sanga or Sanga–Muana–Rina.
A consistent circular arrangement is:
Dinga, Sanga, Muana, Rina, Puia, Thanga.
Here, Puia sits opposite Rina.
So the correct answer is Rina.
A diac is ____ switch.
A)
an AC
B)
a mechanical
C)
a dc
D)
both ac and dc
A DIAC is a bidirectional trigger device used mainly in AC circuits. It conducts only after the breakover voltage is reached and can conduct in both directions, so it is commonly described as an AC switch. It is not a mechanical switch, and it is not used as a DC switch because it needs alternating polarity for normal operation.
Which of the following areas is preferred for solar power plants?
A)
Coastal areas
B)
Hot arid zones
C)
Mountain tops
D)
High rainfall zones
Solar power plants are best suited to areas with high solar insolation, clear skies, low cloud cover, and minimal rainfall. Hot arid zones provide these conditions, so they are preferred for solar power plants. Coastal areas, mountain tops, and high rainfall zones are less ideal due to humidity, cloudiness, or weather constraints.
Vent plug is provided in each lead acid cell to
A)
Pour water or electrolyte when needed
B)
Check the electrolyte level
C)
Allow escape of gases during charging
D)
All of these
In a lead-acid cell, the vent plug is provided to let the gases formed during charging escape safely and to prevent pressure build-up inside the cell. It is not meant for pouring water/electrolyte or checking electrolyte level. Therefore, the correct option is (c).
When a synchronous motor is running at synchronous speed, the damper winding produces
A)
damping torque
B)
eddy current torque
C)
torque aiding the developed torque
D)
no torque
In a synchronous motor, once the rotor reaches synchronous speed, there is no relative motion between the rotating magnetic field and the damper winding. Since induced current in the damper bars depends on relative motion, no emf is induced and therefore no torque is produced by the damper winding. Damper winding mainly helps during starting and in damping oscillations, not at synchronous speed.