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Past Questions — 2026
The SCR(Silicon Controlled Rectifier) is also called a:
A)
Diode
B)
Transistor
C)
Triac
D)
Thyristor
An SCR (Silicon Controlled Rectifier) is a type of controlled semiconductor device known as a thyristor. It has four layers and is used for switching and control in power electronics. It is not a diode (two-layer, unidirectional without gate control), not a transistor (current-controlled/amplifying device), and not a triac (a bidirectional thyristor used for AC control).
What is the primary purpose of the choke (ballast) in a fluorescent lamp circuit?
A)
To produce light
B)
To act as a starter
C)
To limit the current
D)
To improve power factor
In a fluorescent lamp circuit, the choke (ballast) is connected in series with the lamp to restrict the current after ignition. Since a fluorescent lamp has a negative resistance characteristic, without a ballast the current would rise excessively and damage the lamp. The starter’s job is to help initiate the arc, not the choke. The choke also does not produce light, and power factor improvement is not its primary purpose.
Wind energy is harnessed as _______ energy with the help of Windmill or Turbine.
A)
mechanical
B)
electrical
C)
solar
D)
heat
Wind energy is first captured by a windmill or turbine and converted into mechanical energy of rotation. This mechanical energy can then be used directly or further converted into electrical energy by a generator. Hence, the correct answer is mechanical. The other options are incorrect because solar and heat are unrelated, and electrical is not the first form obtained by the windmill/turbine itself.
The rated speed of an induction motor is 1410 rpm. What is meant by the statement “the slip S=0”?
A)
The speed of the motor is higher than the synchronous speed
B)
The motor runs at a synchronous speed
C)
The motor runs at its rated speed
D)
The rotor is stationary.
Slip in an induction motor is defined as S = (Ns - Nr) / Ns, where Ns is synchronous speed and Nr is rotor speed. If S = 0, then Nr = Ns, meaning the rotor runs exactly at synchronous speed. This is the condition corresponding to option (b). Option (a) is impossible because motor speed cannot exceed synchronous speed in normal induction motor operation. Option (c) is incorrect because rated speed is usually slightly less than synchronous speed due to slip. Option (d) is incorrect because a stationary rotor gives slip = 1, not 0.
The value of concentration ratio of flat plate collector is:
A)
1
B)
10
C)
100
D)
1000
A flat plate collector does not use optical concentration; it receives solar radiation directly over its entire absorber area. Therefore, its concentration ratio is 1. Concentrating collectors, such as parabolic troughs or dish collectors, have concentration ratios greater than 1, so options 10, 100, and 1000 are incorrect.
What type of Generator is used in Wind Power Plant?
A)
Synchronous Generator
B)
Induction Generator
C)
Both (a) and (b)
D)
None of the above
Wind power plants can use either synchronous generators or induction generators. Modern wind turbines commonly use induction generators, while some designs also use synchronous generators, especially in variable-speed systems. Therefore, both options (a) and (b) are correct.
Which of the following components of a wind turbine system is arranged in the order in which energy is being converted?
A)
Blades – rotor – electric generator – shaft
B)
Blades – rotor – shaft – electric generator
C)
Shaft – blades – rotor – electric generator
D)
Electric generator – blades – rotor — shaft
In a wind turbine, wind energy first strikes the blades, causing the rotor to turn. The rotor transfers this mechanical motion to the shaft, and the shaft drives the electric generator to produce electricity. So the correct sequence of energy conversion is Blades → Rotor → Shaft → Electric generator. The other options place the components in the wrong order.
The incoming solar radiation on the earth is known as:
A)
Insolation
B)
Beam Radiation
C)
Diffuse Radiation
D)
Terrestrial radiation
The incoming solar radiation received by the Earth is called insolation (incoming solar radiation). Beam radiation is the direct component of sunlight, diffuse radiation is the scattered component, and terrestrial radiation is the heat energy emitted by the Earth back into the atmosphere.
In an induction motor, which of the following factors determine the speed of the motor?
A)
Frequency of the supply
B)
Resistance of the rotor
C)
Number of poles in the motor
D)
Voltage applied to the stator
The speed of an induction motor is primarily determined by the synchronous speed, given by Ns = 120f / P, where f is the supply frequency and P is the number of poles. Therefore, the supply frequency directly affects the motor speed. The number of poles also affects synchronous speed, but among the given single-answer options, the factor most directly determining the speed is the frequency of the supply. Rotor resistance mainly affects slip and starting torque, not the synchronous speed. Stator voltage affects torque and current, not the set speed.
During charging the specific gravity of the electrolyte of a lead acid battery:
A)
increases
B)
decreases
C)
remain the same
D)
becomes zero
In a lead-acid battery, charging converts lead sulphate on the plates back into lead dioxide and lead, and the electrolyte becomes richer in sulphuric acid. As the acid concentration increases, the specific gravity of the electrolyte increases. So option (a) is correct. Option (b) is wrong because specific gravity does not decrease during charging; option (c) is wrong because it changes; option (d) is incorrect because it never becomes zero.
The purpose of conservator in transformer is:
A)
To cool the windings
B)
To prevent moisture in the transformers
C)
To take up contraction and expansion of oil
D)
None of these
A conservator is an oil reservoir fitted on top of an oil-immersed transformer. It provides space for the transformer oil to expand when heated and contract when cooled, maintaining the oil level in the main tank. It also helps reduce direct exposure of oil to air. Hence, the correct purpose is to take up contraction and expansion of oil. Option (a) is incorrect because cooling is mainly done by radiators/cooling tubes, and (b) is not the main purpose of the conservator.
How many thyristors are used in a three-phase full converter bridge?
A)
3
B)
4
C)
6
D)
12
A three-phase full converter bridge uses 6 thyristors. In a three-phase fully controlled bridge rectifier, each phase contributes two thyristors, giving a total of 6 devices. Hence option (c) is correct. The other options are incorrect because 3 and 4 are too few for a three-phase full bridge, and 12 is more than required.
Electrolyte used in a lead acid cell is:
A)
NAOH
B)
H2SO4
C)
Water
D)
Diluted H2SO4
In a lead-acid cell, the electrolyte is dilute sulfuric acid (H2SO4 mixed with water). It provides the ions needed for the electrochemical reaction. NAOH is not used in a lead-acid battery, and pure water is not a proper electrolyte. Although H2SO4 is the acid, the correct practical electrolyte is diluted H2SO4.
The range of wind speed suitable for wind power generator is:
A)
0 to 5 m/s
B)
5 m/s to 25 m/s
C)
25 m/s to 50 m/s
D)
50 m/s to 75 m/s
Wind turbines generally start producing useful power at around 3–5 m/s (cut-in speed) and operate efficiently up to about 20–25 m/s. Above this range, turbines are usually shut down for safety at very high wind speeds (cut-out speed). Therefore, the suitable range given in the options is 5 m/s to 25 m/s. The other options are too low or too high to be the normal operating range.
A series combination of solar cells is known as:
A)
Solar module
B)
Solar array
C)
Solar inverter
D)
Solar tracker
A series combination of solar cells is called a solar module (or solar panel). Multiple solar cells are connected in series to form a module, which increases the voltage. A solar array is a combination of multiple modules, while a solar inverter converts DC to AC and a solar tracker changes the panel orientation to follow the sun.
In which application is a Gate Turn Off thyristor(GTO) used?
A)
Audio amplifier
B)
Power inverter and motor driver
C)
High speed communication system
D)
Low power digital circuits
A Gate Turn-Off thyristor (GTO) is a high-power semiconductor device that can be turned ON by a gate pulse and turned OFF by a negative gate signal. Because of this controllable switching ability, it is commonly used in high-power applications such as power inverters, choppers, and motor drives. Audio amplifiers, high-speed communication systems, and low-power digital circuits use different types of devices and are not typical applications of GTOs.
Distribution transformers have:
A)
smaller size than Power Transformer
B)
larger size than power transformers
C)
size can be more or less depending on type
D)
more weight than power transformers
Distribution transformers are designed for step-down use near consumers and generally handle lower power ratings than power transformers. Because of their lower rating, they are smaller in size and lighter than power transformers. Option (b) is the opposite, (c) is incorrect because the usual comparison is clear, and (d) is wrong because distribution transformers do not weigh more than power transformers.
What gets deposited on the plates of a discharged lead-acid battery?
A)
PbO
B)
Pb2O4
C)
Pb
D)
PbSO4
In a lead-acid battery, during discharge both the positive and negative plates get converted into lead sulfate (PbSO4). This is the deposited product on the plates of a discharged battery. PbO and Pb2O4 are not the discharge products, and Pb is the active material of the negative plate in the charged state, not the deposited substance after discharge.
Transformer works on the principal of :
A)
Fleming’s right hand rule
B)
Fleming’s left hand rule
C)
Faraday’s law of Electromagnetic Induction
D)
Ohm’s law
A transformer operates on the principle of mutual induction, which is based on Faraday’s law of electromagnetic induction. When an alternating current flows in the primary winding, it produces a changing magnetic flux in the core, inducing an EMF in the secondary winding. Fleming’s rules apply to motors/generators, not transformers, and Ohm’s law does not describe the transformer’s working principle.
What is the primary function of a wind turbine in a wind power plant?
A)
To store wind energy
B)
To convert wind energy into mechanical energy
C)
To absorb sunlight and convert it into electricity
D)
To convert electrical energy into mechanical energy
A wind turbine captures the kinetic energy of moving air and converts it into mechanical rotation of the turbine shaft. This mechanical energy is then used to drive a generator for producing electricity. Option (a) is incorrect because turbines do not store wind energy. Option (c) describes a solar panel, not a wind turbine. Option (d) describes an electric motor, not a wind turbine.
What is the most common reason for a ceiling fan not starting?
A)
Broken blade
B)
Faulty capacitor
C)
Damaged bearing
D)
Loose canopy
A ceiling fan commonly fails to start because the capacitor provides the necessary phase shift and starting torque to the motor. If the capacitor is weak or faulty, the fan may only hum or not start at all. A broken blade mainly affects balance, a damaged bearing usually causes noise or slow rotation, and a loose canopy is generally a mounting issue, not the usual reason for failure to start.
What is the first step in troubleshooting a fan that has completely stopped working?
A)
Replace the motor
B)
Replace the regulator
C)
Check the power supply and circuit breaker
D)
Change the blades
The first step in troubleshooting any fan that has completely stopped working is to check whether power is reaching the appliance. This means verifying the power supply, switch, plug, and circuit breaker/fuse. If there is no supply, the fan cannot run regardless of its internal parts. Replacing the motor, regulator, or blades should only be considered after confirming that power is available and the electrical circuit is intact.
In an induction motor, the rotor input is 600 W and slip is 4%. The rotor copper loss is:
A)
700 W
B)
0.6 KW
C)
650 W
D)
24 W
For an induction motor, rotor copper loss = slip × rotor input. Here, slip = 4% = 0.04 and rotor input = 600 W. So rotor copper loss = 0.04 × 600 = 24 W. The other options do not match this direct formula.
In what form is solar energy radiated from the sun?
A)
Ultraviolet Radiation
B)
Infrared radiation
C)
Electromagnetic waves
D)
Transverse waves
Solar energy travels from the Sun through space as electromagnetic radiation. This includes visible light, infrared, ultraviolet, and other parts of the electromagnetic spectrum. So the most correct and general answer is (c) Electromagnetic waves. Option (a) and (b) are only specific parts of the spectrum, not the full form of solar energy. Option (d) is too general and does not specifically describe the radiation from the Sun.
Starter is used in Induction motor because:
A)
Its starting torque is high
B)
It is run against heavy load
C)
It cannot run in reverse direction
D)
Its starting current is 5 times or more than its rated current
An induction motor draws a very large current at the moment of starting because its slip is 1 and the rotor is stationary. This starting current is commonly about 5 to 8 times the rated current. A starter is therefore used to limit the inrush current and protect the motor and supply system. Option (a) is incorrect because starting torque is not the reason for using a starter; rather, the issue is excessive current. Options (b) and (c) are irrelevant to the need for a starter.