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Past Questions
Choose the correct order, from left to right, in which these parts should be placed in order to form the object.
A)
3 1 4 2
B)
3 4 1 2
C)
3 2 4 1
D)
1 2 3 4
The correct left-to-right arrangement is 3 2 4 1, so option c is correct. This sequence matches the way the parts interlock to form a continuous object: part 3 provides the left end, part 2 fits next to it, part 4 continues the central shape, and part 1 completes the right end. The other options are incorrect because they place at least one part in a position where its connecting edges or contours do not align with the neighboring part, breaking the overall shape continuity.
An Auto-transformer (which has only one winding) may be used as a
A)
Step-Up Transformer
B)
Step-Down Transformer
C)
Both Step-Up and Step-Down transformer
D)
None of these
An auto-transformer has a single continuous winding with taps, so it can operate in two ways: as a step-up transformer when the output is taken from a higher-voltage section, and as a step-down transformer when the output is taken from a lower-voltage section. Hence, it can be used as both step-up and step-down transformer. Therefore, option (c) is correct.
The power factor of a 3-phase induction motor at no load is approximately
A)
0.2
B)
0.7
C)
0.85
D)
1
A 3-phase induction motor at no load draws a large magnetizing current to establish the air-gap flux, so its current is highly reactive. Hence the no-load power factor is very low, typically around 0.2 to 0.3. Among the given options, 0.2 is the best answer. Options 0.7, 0.85, and 1 correspond to much better power factors, which are not typical for no-load induction motors.
What is the maximum possible output of a solar array?
A)
300 W/m2
B)
100 W/m2
C)
250 W/m2
D)
500 W/m2
A solar array’s practical maximum output is typically taken as about 300 W/m² under very good operating conditions. This is the highest among the given options. 100 W/m² and 250 W/m² are lower than the usual peak practical value, while 500 W/m² is unrealistically high for a standard solar array output in this exam context.
The chemical used in the breather is:
A)
Sodium chloride
B)
Silica sand
C)
Silica gel
D)
Copper silicate gel
In a transformer breather, the chemical used is silica gel. It absorbs moisture from the air entering the transformer tank, keeping the insulating oil dry. Sodium chloride and silica sand are not used for this purpose, and copper silicate gel is not the standard desiccant in transformer breathers.
In a dc motor, if the field coils get opened, the speed of the motor will
A)
Decrease
B)
Come to a stop
C)
Increase
D)
None of these
In a DC motor, speed is approximately proportional to back EMF divided by field flux. If the field coils open, the field current becomes zero, so the flux weakens drastically. With very weak flux, the motor tries to speed up sharply. In a shunt motor this may cause dangerous overspeeding. Therefore, the speed will increase. The other options are incorrect because the motor does not normally stop immediately, and it certainly does not decrease in speed when field flux is lost.
The friction losses in Real Transformers are
A)
0%
B)
5%
C)
25%
D)
50%
A transformer is a static electrical device with no moving parts, so there is no mechanical friction. Therefore, friction losses in a real transformer are 0%. The other options are not correct because they suggest mechanical losses that do not occur in transformers.
The maximum torque in a 3-phase induction motor occurs at a slip
A)
R/X
B)
X/R
C)
R2/X
D)
R2/X
For a 3-phase induction motor, the condition for maximum torque is when rotor resistance per phase equals slip reactance per phase: R2 = sX2. Hence slip at maximum torque is s = R2/X2, often written simply as R/X in simplified MCQ form. Among the given options, (a) R/X matches this relationship. Options (b), (c), and (d) do not represent the correct slip expression.
The rating of transformer may be expressed in
A)
kw
B)
kVAR
C)
kVA
D)
Horse power
A transformer is rated in kVA because its capacity depends on voltage and current, not on the power factor of the load. Since core loss depends mainly on voltage and copper loss depends on current, the transformer rating is based on apparent power (V × I), i.e., kVA. kW would depend on power factor, kVAR is for reactive power, and horsepower is used for mechanical machines, not transformers.
The current density of a photo voltaic cell ranges from
A)
10-20 mA/cm2
B)
40-50 mA/cm2
C)
20-40 mA/cm2
D)
60-100 mA/cm2
A photovoltaic cell typically produces a current density in the range of about 20 to 40 mA/cm² under standard illumination conditions. This is the commonly accepted range for solar cells in basic renewable energy/electrical engineering MCQs. Option (a) is generally too low, while (b) and (d) are higher than the usual current density range for a PV cell.
The normal way to close a SCR is by approximate
A)
Gate current
B)
Cathode current
C)
Anode current
D)
Forward current
An SCR is turned ON by a gate pulse, but it is normally turned OFF by reducing the anode current below the holding current. In other words, the normal way to close (switch off) an SCR is by removing/reducing the anode current. Gate current is used only for triggering, not for turn-off. Cathode current and forward current are not the standard term for the normal turn-off method.
The installed capacity of wind energy in India is about
A)
8000 MW
B)
1500 MW
C)
6000 MW
D)
4000 MW
The installed wind energy capacity in India around the period of this exam is approximately 8,000 MW, which matches option (a). The other values are too low for India’s wind-energy capacity at that time.
The Transformer core laminations are insulated from each other by:
A)
Paper
B)
Thin varnish coating
C)
Mica strip
D)
All the above can be used for insulation
Transformer core is made of thin steel laminations to reduce eddy current loss. Each lamination is insulated from the next by a thin insulating coating, commonly varnish or oxide layer. Paper and mica are not the standard insulation used between core laminations, so 'Thin varnish coating' is the correct answer.
In a 3-phase controlled bridge rectifier, with an increase of an overlap angle, the output dc voltage
A)
Decreases
B)
Increases
C)
Does not change
D)
Depends upon load inductance
In a 3-phase controlled bridge rectifier, overlap occurs because of source inductance during commutation. As the overlap angle increases, more of the input supply is effectively shorted/shared between outgoing and incoming devices, reducing the average dc output voltage. Therefore, the output dc voltage decreases. The other options are incorrect because the voltage is not unchanged, does not increase with overlap, and while load inductance can affect current continuity, the effect of overlap angle on average dc output voltage is a general reduction.
Chopper control for DC motors provides variation in
A)
Input voltage
B)
Frequency
C)
Both (a) and (b)
D)
None of these
A chopper is a DC-to-DC converter used in DC motor speed control. It varies the average DC voltage supplied to the motor by switching the input on and off rapidly. The output frequency is not the main controlled quantity here; the control is essentially by changing the input voltage level. Hence, the correct answer is input voltage.
Maximum wind energy available is proportional to:
A)
Air density
B)
Cube of wind velocity
C)
Square of the rotor diameter
D)
All of these
The maximum wind power available is given by the expression P = (1/2) × ρ × A × V^3, where ρ is air density, A is the swept area of the rotor, and V is wind velocity. Since swept area A is proportional to the square of rotor diameter, the available wind energy is proportional to air density, cube of wind velocity, and square of rotor diameter. Therefore, all the given factors are correct.
Which of the following conditions is necessary for triggering system for thyristors?
A)
It should be synchronized with the main supply
B)
It must use separate power supply
C)
It should provide a train of pulses
D)
None of these
A thyristor triggering system must deliver gate pulses in a reliable manner, and in practice a train of pulses is used so that the device can turn on even if the first pulse is missed or the device is not ready at that instant. Synchronization with the main supply is generally required for phase control, but it is not the essential triggering condition itself. A separate power supply is not necessary as a general condition. Therefore, the correct answer is that it should provide a train of pulses.
The maximum value of torque that a synchronous motor, can develop without losing its synchronism, is known as
A)
breaking torque
B)
synchronizing torque
C)
pull out torque
D)
slip torque
In a synchronous motor, the maximum torque it can develop while still remaining in step with the supply frequency is called the pull-out torque. If the load exceeds this value, the motor loses synchronism.
- Breaking torque: not the standard term for this limit in synchronous motors.
- Synchronizing torque: the torque that tends to restore synchronism after a small disturbance, not the maximum permissible torque.
- Slip torque: associated with induction motors, not synchronous motors.
Hence, the correct answer is pull out torque.
A 3-phase 50 Hz induction motor runs at speed of 940 RPM; the speed of the rotating magnetic field will be:
A)
940 RPM
B)
1000RPM
C)
1050RPM
D)
1100RPM
For a 3-phase induction motor, the rotating magnetic field moves at synchronous speed: Ns = 120f / P. The rotor speed is 940 RPM, which must be slightly less than synchronous speed due to slip. Among the given options, 1000 RPM is the only plausible synchronous speed. It corresponds to a 6-pole, 50 Hz motor: Ns = 120 × 50 / 6 = 1000 RPM. The other options are not suitable as the field speed must be higher than rotor speed.
For ceiling fans generally the single phase motor used is
A)
split phase type
B)
capacitor start type
C)
capacitor start and run type
D)
permanent capacitor type
Ceiling fans generally use a single-phase capacitor-run motor, also called a permanent split capacitor (PSC) motor or permanent capacitor type. The capacitor remains in the circuit during running to improve power factor, efficiency, and starting/running performance. Split-phase motors and capacitor-start motors are more common in applications needing high starting torque, while ceiling fans need smooth, quiet, continuous operation rather than high starting torque. Hence, the correct answer is permanent capacitor type.
Under the influence of fluorescent lamps sometimes the wheels of rotating machinery appear to be stationary. This is due to the
A)
fluctuations
B)
luminescence effect
C)
stroboscopic effect
D)
low power factor
Fluorescent lamps produce light that fluctuates at twice the supply frequency. If a rotating machine is illuminated by such light, the periodic variation in light can make the moving parts appear stationary or moving slowly. This illusion is called the stroboscopic effect. The other options do not explain this visual phenomenon: fluctuations are only the cause in general, luminescence effect is unrelated, and low power factor has no connection with apparent motion.
A substitute for “one who likes to spend time with others” in one word can be
A)
Introvert
B)
Commoner
C)
Extrovert
D)
Extraordinary
An extrovert is a person who enjoys being with others and is sociable. This matches the phrase “one who likes to spend time with others.”
- Introvert: a person who prefers solitude or less social interaction.
- Commoner: an ordinary person, not related to social behavior.
- Extraordinary: unusual or exceptional, not a substitute here.
So, the correct answer is Extrovert.
When the SCR conducts, the forward voltage drop
A)
is 0.7V
B)
is 1 to 1.5V
C)
increases slightly with load current
D)
remains constant with load current
When an SCR is in the ON state, it behaves like a low-resistance switch, but its forward voltage drop is not perfectly constant. As the anode current (load current) increases, the forward voltage drop increases slightly due to internal conduction characteristics. Hence, option (c) is correct. Option (a) and (b) are typical diode voltage drops, not SCR-specific values, and option (d) is incorrect because the drop does not remain perfectly constant.
A module in a solar panel refers to
A)
Series arrangement of solar cells
B)
Parallel arrangement of solar cells
C)
Series and parallel arrangement of solar cells
D)
None of these
A solar module (solar panel) is formed by connecting individual solar cells in series and/or parallel to obtain the required voltage and current. Series connection increases voltage, while parallel connection increases current. Therefore, a module refers to a series and parallel arrangement of solar cells. Options (a) and (b) are incomplete, and (d) is incorrect.
The starting torque of a 3-phase induction motor can be increased by increasing
A)
the rotor reactance
B)
the rotor resistance
C)
the stator resistance
D)
none of these
In a 3-phase induction motor, starting torque depends on rotor resistance at standstill (slip = 1). Increasing rotor resistance improves the ratio of resistance to reactance at starting, thereby increasing starting torque up to an optimum value. Rotor reactance alone does not increase starting torque effectively, and stator resistance is generally not used for this purpose because it only causes voltage drop and power loss. Hence, the correct answer is rotor resistance.