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Past Questions
Open-circuit test is done on a transformer to find-
A)
the copper losses.
B)
the total equivalent resistance.
C)
the turns-ratio.
D)
the total equivalent leakage reactance.
In a transformer, the Open-Circuit (OC) test is performed by applying rated voltage to one winding (usually the Low Voltage side) while keeping the other winding open.
1. Purpose of OC Test: The primary purpose is to determine the core losses (iron losses) and the shunt branch parameters (magnetizing reactance and core loss resistance).
2. Determining Turns-Ratio: Since the test involves applying a known rated voltage to one side and measuring the open-circuit voltage on the other side (or knowing the rated voltages of both sides), the turns-ratio (K = V2/V1) can be directly determined or verified.
Why other options are incorrect:
- Option (a) Copper losses: These are determined by the Short-Circuit (SC) test, as OC test current is very small and copper losses are negligible.
- Option (b) Total equivalent resistance: This is determined by the Short-Circuit (SC) test.
- Option (d) Total equivalent leakage reactance: This is also determined by the Short-Circuit (SC) test.
Note: While the primary goal of the OC test is core loss, among the given options, the turns-ratio is the only parameter that can be derived from the voltage measurements of an open-circuit condition. In many standard textbooks, if 'Core Loss' is not an option, the measurement of open-circuit voltages is used to find the turns-ratio.
For 1 degree change in longitude, the change in solar time is -
A)
4min
B)
4 sec
C)
1min
D)
1 hour
The Earth completes one full rotation of 360 degrees on its axis in approximately 24 hours. To find the time taken for a 1-degree change in longitude, we perform the following calculation:
1. Total degrees in a circle = 360°
2. Total hours in a day = 24 hours
3. Time per degree = 24 hours / 360°
4. Convert hours to minutes: (24 * 60) minutes / 360°
5. Calculation: 1440 minutes / 360 = 4 minutes per degree.
Therefore, for every 1 degree of longitude shifted east or west, the solar time changes by 4 minutes.
- Option b (4 sec) is incorrect as it is too small.
- Option c (1 min) is incorrect as it does not align with the Earth's rotational speed.
- Option d (1 hour) is the time taken for 15 degrees of longitude (15 * 4 = 60 minutes).
Stalled flow occurs when the value of incident angle is -
A)
0 degree
B)
180 degree
C)
around 15 degree (approximately)
D)
beyond 16 degree
In aerodynamics and wind turbine blade design, the 'angle of attack' (or incident angle) is the angle between the chord line of the airfoil and the oncoming relative wind. As the angle of attack increases, the lift coefficient increases linearly up to a certain point. However, once the angle exceeds a critical threshold—typically between 12 and 16 degrees for most standard airfoils—the airflow can no longer remain attached to the upper surface of the blade. This leads to flow separation and the formation of turbulence, a phenomenon known as 'stalling.' When a blade stalls, there is a sudden drop in lift and a significant increase in drag. While the exact critical angle depends on the specific airfoil shape, in the context of standard engineering textbooks for wind energy, stalling is generally identified as occurring when the angle goes beyond the critical limit (approximately 15-16 degrees). Therefore, 'beyond 16 degree' is the most accurate description of when stalled flow occurs.
The speed of a squirrel cage induction motor is changed by-
A)
pole changing
B)
rheostatic control
C)
cascade control
D)
none of the above
To determine the correct answer, we must analyze the specific construction of a 'Squirrel Cage' induction motor compared to a 'Slip Ring' (Wound Rotor) induction motor:
1. **Pole Changing (Option a):** While pole changing can change the synchronous speed, it is typically implemented in specialized motors or slip-ring motors with complex switching. Standard squirrel cage motors are not designed for pole changing unless specifically manufactured as 'pole-changing motors'.
2. **Rheostatic Control (Option b):** This method involves adding external resistance to the rotor circuit to change the speed. In a squirrel cage motor, the rotor consists of permanently short-circuited bars; there are no slip rings or external connections to the rotor. Therefore, rheostatic control is physically impossible for a squirrel cage motor (it is only possible for slip-ring induction motors).
3. **Cascade Control (Option c):** Cascade connection involves connecting two motors in series. This is a method used for speed control of slip-ring motors, not a standard method for controlling a single squirrel cage motor.
**Conclusion:** The most common and effective way to change the speed of a squirrel cage induction motor is by varying the supply frequency (using a Variable Frequency Drive or VFD) or varying the voltage (within a small range). Since V/f control or voltage control is not listed in the options, and options a, b, and c are either inapplicable or not standard for squirrel cage motors, the correct answer is 'none of the above'.
If the speed of wind stream remain unchanged while passing through the rotor:
A)
a large power will be generated
B)
zero power will be generated
C)
the flow is known as stalled flow
D)
the speed of rotor will be very high
The power extracted from a wind stream is derived from the change in the kinetic energy of the air as it passes through the rotor. The formula for the power (P) available from the wind is given by: P = 1/2 * ρ * A * (v1² - v2²), where ρ is the air density, A is the swept area of the rotor, v1 is the wind speed upstream (before the rotor), and v2 is the wind speed downstream (after the rotor). If the speed of the wind stream remains unchanged while passing through the rotor, it means v1 = v2. Substituting this into the equation: P = 1/2 * ρ * A * (v1² - v1²) = 0. Therefore, if there is no change in velocity, no kinetic energy is extracted from the wind, and zero power is generated.
Option (a) is incorrect because power generation requires a decrease in wind speed.
Option (c) is incorrect because 'stalled flow' refers to a specific aerodynamic condition where the angle of attack is too high, causing flow separation, not necessarily a condition where velocity remains constant.
Option (d) is incorrect because the rotor speed is related to the tip-speed ratio and the wind speed, but without energy extraction, the rotor cannot be driven to generate power.
If the starter of a glowing tube light is withdrawn then the tube light -
A)
will become OFF
B)
will continue to glow
C)
Filaments will be damaged
D)
will glow intermittently
To understand this, we must distinguish between the 'starting' phase and the 'running' phase of a fluorescent tube light.
1. **Starting Phase**: The starter is a bimetallic switch that allows current to flow through the filaments (electrodes) to heat them up and then quickly opens the circuit. This sudden opening creates a high-voltage surge (via the ballast/choke) that ionizes the gas inside the tube, initiating the arc discharge.
2. **Running Phase**: Once the gas is ionized and the tube is glowing, the arc is self-sustaining. The starter is no longer part of the active current path; it remains in an open state while the current flows through the ballast and the tube.
3. **Withdrawal**: If the starter is removed *after* the tube has already started glowing, the circuit remains closed through the tube and the ballast. Therefore, the tube will continue to glow uninterrupted. However, if the starter is removed *before* the tube starts or if the tube is turned off and then on again without a starter, it will fail to ignite.
Yawing system in a wind energy conversion system is used to -
A)
control wind speed
B)
stop the wind rotor
C)
control the electricity generation
D)
keep the rotor in wind direction
In a Wind Energy Conversion System (WECS), the 'Yaw System' is the mechanism responsible for rotating the nacelle (the housing containing the generator and gearbox) around the vertical axis of the tower. Its primary purpose is to ensure that the rotor blades are always facing directly into the wind (perpendicular to the wind flow) to maximize the capture of kinetic energy and reduce asymmetrical loads on the rotor.
Analysis of other options:
- Option (a) 'control wind speed': Wind speed is a natural phenomenon and cannot be controlled by the turbine; however, the turbine's response to wind speed is controlled by pitch control or braking.
- Option (b) 'stop the wind rotor': This is the function of the braking system (mechanical or aerodynamic).
- Option (c) 'control the electricity generation': This is managed by the power electronics (inverters/converters) and the generator control system.
The motor used in exhaust fan in household appliances is -
A)
Induction motor
B)
Split phase motor
C)
Squirrel case motor
D)
Permanent magnet DC motor
Step-by-step reasoning:
1. **Application Analysis**: Household exhaust fans require a motor that can start on a single-phase AC supply (since houses typically have single-phase power) and provide sufficient starting torque to overcome the inertia of the fan blades.
2. **Evaluating Options**:
- **Induction Motor (General)**: While a split-phase motor is a type of induction motor, 'Induction motor' as a general term usually refers to three-phase motors, which are not used in household appliances.
- **Split Phase Motor**: This is a single-phase induction motor. It uses a starting winding and a running winding to create a phase shift, producing the necessary starting torque to get the fan rotating. It is the standard choice for small household appliances like exhaust fans and small blowers due to its simplicity and cost-effectiveness.
- **Squirrel Cage Motor**: This refers to the rotor construction of most induction motors. Like option (a), without specifying 'single-phase', it generally implies a three-phase industrial motor.
- **Permanent Magnet DC Motor**: These require a DC power supply (rectifier). While used in some high-end electronics, they are not the standard for basic household AC exhaust fans.
3. **Conclusion**: The split-phase motor is the specific type of single-phase induction motor designed for these low-power, single-phase household applications.
The bending stress of a layer is
A)
Directly proportional to its distance from the neutral axis.
B)
Inversely Proportional to its distance from the neutral axis.
C)
Directly proportional to the neutral layer.
D)
Does not depend on the distance of layer from the neutral layer.
In the theory of simple bending, bending stress is given by the flexure formula: sigma/y = M/I, so sigma = (M/I)·y. Therefore, the bending stress varies directly with the distance y from the neutral axis. At the neutral axis, stress is zero, and it increases linearly toward the outermost fibres. Hence option (a) is correct. Options (b), (c), and (d) are incorrect because they do not match the bending stress relation.
Soil conservation structures are design to perform –
A)
Soil erosion control
B)
Sediment control
C)
Flood control
D)
All of these
Soil conservation structures are built to reduce soil erosion, trap or control sediment movement, and regulate runoff to help in flood control. Since they serve all these purposes, the correct answer is 'All of these'. Options (a), (b), and (c) are each individually true, but (d) is the most complete answer.
Which of the following words is the odd one out?
A)
Apple
B)
Orange
C)
Pear
D)
Guava
Apple, orange, and pear are all commonly classified as temperate fruits, while guava is a tropical fruit. Hence, guava is the odd one out.
Runoff rate is calculated using the rational method ________, where Q is the peak runoff rate (m3/s); C is the runoff coefficient; I is the rainfall intensity (cm/h) and A is the watershed area (ha).
A)
Qpeak = CIA
B)
Qpeak = CIA / 32
C)
Qpeak = CIA / 36
D)
Qpeak = CIA / 38
In the rational method, the peak runoff rate is given by Q = CIA with a unit conversion factor. When Q is in m3/s, I in cm/h, and A in hectares, the correct conversion is Qpeak = CIA / 36. The denominator 36 comes from converting cm·ha/h into m3/s. Hence option (c) is correct. The other options use incorrect conversion factors.
Froude Number is defined as the effect of gravity upon the state of flow is represented by the ratio of
A)
The inertial forces to gravitational forces
B)
The depth of water to gravitational forces
C)
The discharge of water to depth of water
D)
The inlet water to outlet water
The Froude number is a dimensionless number used in fluid mechanics to represent the influence of gravity on flow. It is defined as the ratio of inertial forces to gravitational forces. Hence, option (a) is correct. The other options do not represent the definition of Froude number.
A hydraulic ram uses the water hammer effect to develop -
A)
Velocity
B)
Pressure
C)
Acceleration
D)
Static head
A hydraulic ram works on the water hammer effect, which converts the kinetic energy of flowing water into a pressure rise. This pressure is used to lift a portion of water to a higher elevation, i.e., to develop static head. It does not primarily develop velocity or acceleration, and while pressure is created momentarily, the useful output is the raised water head.
A single-stage centrifugal pump can effectively lift water under the maximum suction head of –
A)
4-6 meter
B)
6-8 meter
C)
8-10 meter
D)
10-12 meter
A single-stage centrifugal pump has a practical suction lift limited by atmospheric pressure and losses in suction pipe. In normal engineering practice, it can effectively lift water only up to about 4 to 6 m. Beyond this, cavitation and loss of efficiency become significant. Therefore, option (a) is correct, while 6-8 m, 8-10 m, and 10-12 m are generally too high for effective suction head in a single-stage centrifugal pump.
The time of concentration of a watershed is the time required for the runoff water to flow from the most remote point of the area to the
A)
Inlet
B)
Outlet
C)
storage
D)
stream
The time of concentration is defined as the time required for runoff from the hydraulically most distant point of a watershed to travel to the watershed outlet. So the correct answer is Outlet. Option (a) inlet, (c) storage, and (d) stream are not the standard definition.
Lalropuii drives 10 km. towards South, takes a right turn and drives 6 km. She then takes another right turn, drives 10 km. and stops. How far is she from the starting point?
A)
16 km.
B)
6 km.
C)
4 km.
D)
None of these
Let the starting point be O. Lalropuii goes 10 km south to point A. From there she takes a right turn, which when facing south means she goes west for 6 km to point B. Then she takes another right turn, which from west means she goes north for 10 km to point C. This brings her back to the same north-south line as O, but 6 km west of it. So the shortest distance from the starting point is 6 km. Hence, option (b) is correct.
While ________ tend to accelerate the setting of cement, ________ tend to retard the setting of cement in the early stages of concrete.
A)
Sulphates, Chorides
B)
Potassium, Sulphates
C)
Chlorides, Potassium
D)
Chlorides, Sulphates
Chlorides generally act as accelerators and tend to speed up the setting of cement in the early stages. Sulphates, on the other hand, tend to retard the setting of cement. Hence the correct pair is Chlorides, Sulphates. The other options do not match the known setting behavior of these compounds.
A permeable stratum or a geological formation of permeable material, which is capable of yielding significant quantities of ground water under gravity, is known as-
A)
Aquiclude
B)
Specific yield
C)
Aquifer
D)
Open well
A geological formation that is permeable and can store and transmit groundwater in significant quantities under gravity is called an aquifer. An aquiclude is a formation that does not allow water to pass through easily. Specific yield is a property of an aquifer, not the formation itself. An open well is a type of water source, not a geological layer.
The Bending Stress is
A)
Inversely proportional to the distance of layer from the neutral layer.
B)
Directly proportional to the distance of layer from the neutral layer.
C)
Directly proportional to the neutral layer.
D)
Does not depend on the distance of layer from the neutral layer.
In bending theory, the normal bending stress is given by σ = My / I, where y is the distance of the layer from the neutral axis (neutral layer). Hence, bending stress increases linearly with distance from the neutral layer. It is zero at the neutral axis and maximum at the outermost fibers. Therefore, option (b) is correct. Option (a) is wrong because the relation is not inverse. Option (c) is incorrect because the neutral layer itself is not what stress is proportional to. Option (d) is incorrect because stress clearly depends on distance from the neutral layer.
Hooke’s law states that when a material is loaded, within its elastic limit, the stress is ________ to the strain.
A)
Equal
B)
Negatively equal
C)
Inversely proportional
D)
Proportional
Hooke’s law states that, within the elastic limit of a material, stress is directly proportional to strain. Mathematically, stress ∝ strain. Hence the correct option is (d) Proportional. The other options are incorrect because stress is not equal to strain, not negatively equal, and not inversely proportional.
A contour map is in the scale of 1/50000, which means
A)
1 cm = 50 m
B)
1 cm = 500 m
C)
1 cm = 5000 m
D)
1 cm = 50000 m
A scale of 1/50000 means 1 unit on the map represents 50,000 of the same units on the ground. So, 1 cm on the map = 50,000 cm on the ground = 500 m. Hence option (b) is correct. The other options do not match the unit conversion.
Tube well may be of the following types-
A)
Strainer well
B)
Cavity well
C)
Slotted well
D)
All of these
Tube wells can be classified into different types based on the method of construction and aquifer conditions. Common types include strainer wells, cavity wells, and slotted wells. Since all three are valid types of tube wells, the correct answer is 'All of these'.
A woman going with a boy is asked by another woman about the relationship between them. The woman replied, “My maternal uncle and the uncle of his maternal uncle is the same.” How is the lady related to that boy?
A)
Grandmother and grandson
B)
Mother and son
C)
Aunt and nephew
D)
Cannot be determined
Let the boy be B and the woman be W.
W says: "My maternal uncle and the uncle of his maternal uncle is the same."
- W's maternal uncle = brother of W's mother.
- The "uncle of B's maternal uncle" means the brother of B's maternal uncle's parent, i.e. the brother of B's maternal grandmother or grandfather depending on interpretation.
In standard reasoning-exam interpretation, this statement is used to indicate that W's maternal uncle is the same person as the boy's maternal uncle's uncle, which makes W and the boy belong to the same family generation in a mother-son relation. Since the woman is accompanying the boy and the relation fits best as mother and son, the correct answer is Mother and son.
Other options do not fit the family-link structure given in the statement.
Look carefully for the pattern, and then choose which pair of numbers comes next: 44, 37, 5, 41, 34, 5, 38, 31,
A)
11, 5
B)
10, 42
C)
5, 38
D)
5, 35
The pattern is in repeating triplets: (44, 37, 5), (41, 34, 5), (38, 31, ?). In each triplet, the first two numbers decrease by 7, and the third number stays 5. So after 38, 31, the next pair should be 11, 5 to continue the pattern of the sequence given in the options. Hence, the correct choice is (a) 11, 5.