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Past Questions
The Wind speed is measured using an instrument called:
A)
Hydrometer
B)
Manometer
C)
Anemometer
D)
Wind Vane
Wind speed is measured by an anemometer. A wind vane shows wind direction, not speed. A hydrometer measures the specific gravity of liquids, and a manometer measures pressure difference.
A single phase motor has:
A)
Zero starting torque
B)
Low starting torque
C)
High starting torque
D)
None of the above
A single-phase induction motor is not self-starting. At standstill, the alternating field produced by the single-phase supply can be resolved into two equal and opposite rotating fields, giving no net starting torque. Hence its starting torque is zero. Therefore, option (a) is correct. Option (b) is incorrect because the starting torque is not merely low; it is zero without any starting aid. Option (c) applies to some special motor types or starting arrangements, not a plain single-phase motor.
Which instrument is used to measure direct solar radiation?
A)
Pyranometer
B)
Sunshine Recorder
C)
Pyrheliometer
D)
Anemometer
Direct solar radiation (beam radiation) is measured using a pyrheliometer. A pyranometer measures total or global solar radiation on a surface, a sunshine recorder measures duration of bright sunshine, and an anemometer measures wind speed.
Most of the Solar Cells are made of:
A)
Magnesium
B)
Iron
C)
Radium
D)
Silicon
Most solar cells are made of silicon because it is a semiconductor, which can efficiently convert sunlight into electricity through the photovoltaic effect. Magnesium, iron, and radium are not commonly used as the main material for solar cells.
The Solar Cell efficiency is about:
A)
15%
B)
25%
C)
48%
D)
63%
A typical commercial solar cell has an efficiency of about 15% to 20%. Among the given options, 15% is the closest and standard exam answer. 25%, 48%, and 63% are much higher than usual efficiency values for ordinary solar cells.
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.
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).
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.
A solar cell is basically:
A)
a voltage source, controlled by flux of radiation
B)
a current source, controlled by flux of radiation
C)
an uncontrolled current source
D)
an uncontrolled voltage source
A solar cell is commonly modeled as a current source because the photocurrent it generates is proportional to the incident solar radiation (light flux). The output current changes with radiation intensity, so it is a current source controlled by flux of radiation. Option (a) is incorrect because a solar cell is not primarily modeled as a voltage source. Options (c) and (d) are incorrect because the solar cell output is not independent of illumination.
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 energy has the greatest potential among all the sources of renewable energy?
A)
Solar energy
B)
Wind Energy
C)
Thermal energy
D)
Hydro-electrical energy
Solar energy has the greatest potential among renewable energy sources because the sun provides an immense, continuous supply of energy to the Earth. Compared with wind, hydro, and geothermal/thermal sources, solar is far more abundant and widely available. Wind and hydro depend on specific geographic and climatic conditions, while solar energy is available almost everywhere.
A diac has_________ terminals.
A)
two
B)
three
C)
four
D)
five
A DIAC (Diode for AC) is a two-terminal bidirectional trigger device. It conducts after its breakover voltage is reached in either polarity. Therefore, it has only two terminals. Options (b), (c), and (d) are incorrect because three terminals are associated with devices like TRIACs, not DIACs.
What is the standard value of solar constant?
A)
1 kW/m2
B)
1.367 kW/m 2
C)
1.5kW/m2
D)
5 kW/m2
The solar constant is the amount of solar radiation received per unit area at the outer edge of Earth’s atmosphere on a surface normal to the Sun’s rays at mean Earth–Sun distance. Its standard accepted value is about 1367 W/m², which is 1.367 kW/m². The other options are not the standard solar constant.
A Photovoltaic cell converts sunlight directly into:
A)
Heat energy
B)
Mechanical energy
C)
Electrical energy
D)
Chemical energy
A photovoltaic (PV) cell works on the photovoltaic effect, by which sunlight is directly converted into electrical energy. It does not produce heat as the main output, nor mechanical or chemical energy. Therefore, the correct option is (c) Electrical energy.
The most commonly used semiconductor material is:
A)
Silicon
B)
Germanium
C)
Mixture of Silicon and Germanium
D)
None of the above
Silicon is the most commonly used semiconductor material because it is abundant, inexpensive, thermally stable, and has suitable electrical properties for making diodes, transistors, and integrated circuits. Germanium was used earlier, but silicon replaced it in most applications due to better temperature performance and lower leakage current. A mixture of silicon and germanium is used only in special devices, not as the most common material.
What is the major drawback of wind energy?
A)
High pollution
B)
It is not renewable
C)
Intermittent and variable nature
D)
Low energy efficiency
Wind energy’s main limitation is that it depends on wind availability, which is not constant. Since wind speed changes with weather and time, power generation is intermittent and variable. Option (a) is incorrect because wind energy is clean and has very low pollution during operation. Option (b) is incorrect because wind is a renewable source. Option (d) is not the major drawback; while efficiency and capacity factor matter, the key issue is the unpredictability of supply.
Core of a Transformer is laminated to:
A)
minimize hysteresis loss
B)
minimize Eddy current loss
C)
minimize copper loss
D)
minimize both hysteresis and eddy current loss
The transformer core is laminated into thin insulated sheets to break the path of circulating currents induced in the core. This reduces eddy currents, thereby minimizing eddy current loss. Hysteresis loss depends on the magnetic properties of the core material and is reduced by using suitable materials like silicon steel, not by lamination. Copper loss occurs in the windings due to their resistance, so lamination does not affect it.
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.
Solar PV system are broadly classified into:
A)
1
B)
2
C)
3
D)
4
Solar PV systems are broadly classified into 2 types: (1) stand-alone (off-grid) systems and (2) grid-connected systems. Sometimes hybrid systems are discussed as a combination, but the broad basic classification is into two main categories. Hence, option (b) is correct.
The rotor of a 3 phase induction motor always runs at:
A)
Synchronous speed
B)
Less than synchronous speed
C)
More than synchronous speed
D)
None of these
In a 3-phase induction motor, the rotor must run slightly below synchronous speed so that there is relative motion between the rotating magnetic field and the rotor conductors. This relative motion induces rotor EMF and current, which produce torque. If the rotor reached synchronous speed, no EMF would be induced, so torque would become zero. Hence, the rotor always runs at less than synchronous speed.
A chopper may be thought as:
A)
Inverter with DC input
B)
DC equivalent of an AC transformer
C)
Diode rectifier
D)
DC equivalent of an induction motor
A chopper is a DC-DC converter used to obtain a variable DC output from a fixed DC input. Because a transformer changes AC voltage levels, a chopper is commonly described as the DC equivalent of an AC transformer. Option (a) is incorrect because an inverter converts DC to AC, not DC to variable DC. Option (c) is incorrect because a diode rectifier converts AC to DC. Option (d) is unrelated.
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.
Which tool is essential for checking continuity in an electric iron or heater?
A)
Screwdriver
B)
Multimeter
C)
Pliers
D)
Hammer
A multimeter is used to test electrical continuity by measuring resistance or using its continuity function. In an electric iron or heater, it helps check whether the heating element circuit is complete or broken. Screwdriver, pliers, and hammer are mechanical tools and cannot check electrical continuity.
Function of a Breather in a Transformer is:
A)
to absorb the moisture of air.
B)
to pass cold air to the Transformer.
C)
to insulate the core.
D)
for cooling the temperature.
A breather in an oil-immersed transformer contains silica gel and is fitted to the conservator tank. When the transformer oil expands and contracts, air enters and leaves through the breather. Its function is to remove moisture from the incoming air so that damp air does not contaminate the transformer oil. Therefore, option (a) is correct. Options (b), (c), and (d) are incorrect because the breather is neither used to supply cold air, nor to insulate the core, nor primarily for cooling.
AC voltage controllers convert:
A)
Fixed ac to fixed dc
B)
Variable ac to variable dc
C)
Fixed ac to variable ac
D)
Variable ac to fixed ac
AC voltage controllers are power electronic converters used to control the RMS value of an AC supply without changing its frequency. Thus, they take a fixed AC input and provide a variable AC output. Option (a) describes an AC to DC converter (rectifier), option (b) refers to a chopper/inverter-related conversion but not AC voltage controller, and option (d) is not a standard power conversion category.