← MES Jr. Grade
Past Questions — 2015
A phase-lag compensator will
A)
improve relative stability
B)
increase the speed of response
C)
increase bandwidth
D)
increase overshoot
A phase-lag compensator mainly increases the low-frequency gain of a control system, which improves steady-state accuracy. Its phase effect is negative at higher frequencies, so it generally reduces bandwidth and does not increase speed of response. By improving gain at low frequencies and often allowing better error performance without much change in transient behavior, it is commonly used to improve relative stability compared with uncompensated systems. Hence, the correct option is (a).
The dc motor, which can provide zero speed regulation at full load without any controller is
A)
series
B)
shunt
C)
cumulative compound
D)
differential compound
A DC shunt motor has nearly constant speed from no-load to full-load because its field winding is connected in parallel with the armature, so the field flux remains almost constant. Hence its speed regulation is very small and can be considered approximately zero at full load without any controller. A series motor has poor speed regulation and dangerous high speed at no-load. A cumulative compound motor has better load characteristics than a series motor, but not as constant as a shunt motor. A differential compound motor is unstable and unsuitable for this purpose.
The transfer function of a tachometer is of the form
A)
KS
B)
k/s
C)
k/(S+1)
D)
k/S(S+1)
A tachometer is a velocity-measuring device. Its output voltage is proportional to angular speed, so in Laplace form the transfer function is of the form G(s) = K s when expressed as a differentiating action in control-system representation. Among the given options, this matches KS. The other options represent an integrator (k/s), a first-order lag (k/(s+1)), and an integrator with lag (k/s(s+1)), which are not tachometer characteristics.
A negative feedback closed loop system is supplied to an input of 5 volt. The system has a forward gain of 1 and a feedback gain of 1. What is the output voltage?
A)
1.0 V
B)
2.5 V
C)
1.5 V
D)
2.0 V
For a negative feedback system, the closed-loop transfer function is G / (1 + G H). Here G = 1 and H = 1, so the closed-loop gain is 1 / (1 + 1) = 1/2. With an input of 5 V, the output is 5 × 1/2 = 2.5 V. Hence, option (b) is correct.
The efficiency of a d.c. machine is maximum when
A)
the machine is running at full-load
B)
the machine is running at no-load
C)
the variable loss equals the constant loss
D)
none of these
The efficiency of a d.c. machine is maximum when the total losses are minimum for a given output. For a d.c. machine, losses are divided into constant losses (like iron loss, friction and windage, and shunt field loss) and variable losses (mainly copper loss, which varies with load). Maximum efficiency occurs when variable loss becomes equal to constant loss. At this point, the rate of increase of output and losses is balanced, giving the highest efficiency. Hence, option (c) is correct. Full-load or no-load conditions do not generally give maximum efficiency.
A cylindrical rotor synchronous motor with damper windings is switched on without dc supply to its field windings. It will
A)
not start
B)
start but not run at synchronous speed
C)
start as an induction motor and then run as a synchronous motor
D)
start and run as a synchronous motor
A synchronous motor without DC excitation on the field winding cannot develop synchronous torque. However, because it has damper windings, it can start as an induction motor due to induced currents in the damper bars. Since the field is not excited, it will not pull into synchronism and therefore will not run at synchronous speed. Option (c) is incorrect because transition to synchronous running requires DC field excitation.
Which of the following circuit breakers produce least arc energy?
A)
Air circuit breaker
B)
Oil circuit breaker
C)
Vacuum circuit breaker
D)
Air blast circuit breaker
Arc energy is least in a vacuum circuit breaker because the arc is formed in a high-vacuum medium, where there are very few ionized particles to sustain the arc. As a result, arc extinction is very rapid and the energy dissipated in the arc is minimum. Air circuit breakers and air blast circuit breakers use air as the interrupting medium, so they produce more arc energy than vacuum breakers. Oil circuit breakers also have higher arc energy compared with vacuum breakers because the arc is quenched in oil, not in vacuum.
The advantage of transmitting power at high voltage is
A)
magnitude of current will be small
B)
it will reduce the voltage drop in the line
C)
power loss will be less
D)
all of these
For a given power, transmitting at higher voltage reduces current because P = VI. Lower current means I²R loss in the transmission line is reduced, so power loss is less. Also, with smaller current, the voltage drop across the line (IR drop) is reduced. Therefore, all the listed advantages are correct.
If the armature current is increased to double its previous value, and the time of commutation is halved, how will the reactance voltage vary?
A)
It will be halved
B)
It will remain the same
C)
It will be doubled
D)
It will become four times
Reactance voltage during commutation is proportional to the rate of change of current, approximately V_r ∝ I/t. If the armature current is doubled and the time of commutation is halved, then the reactance voltage changes by a factor of 2 ÷ (1/2) = 4. However, in the standard commutation relation, the reactance voltage is proportional to I divided by commutation time, so doubling current and halving time gives four times the original value. Among the given options, this corresponds to option (d), not (c).
Which of the following plants has the minimum running cost?
A)
nuclear
B)
thermal
C)
hydro
D)
diesel
Among the given options, hydroelectric plants have the minimum running cost because water is a free fuel and the operating expenses are low once the plant is built. Nuclear, thermal, and diesel plants require costly fuel and generally have higher operating costs. Therefore, the correct answer is hydro.
As compared to a closed-loop system, an open-loop system is
A)
more stable as well as more accurate
B)
less stable as well as less accurate
C)
more stable but less accurate
D)
less stable but more accurate
In an open-loop control system, there is no feedback path to compare the output with the desired input. Because of this, the system cannot automatically correct errors or disturbances. Hence, compared to a closed-loop system, an open-loop system is generally less accurate and also less stable. Closed-loop systems use feedback, which improves both accuracy and stability.
Which motor can conveniently operate at lagging as well as leading power factor?
A)
squirrel-cage induction motor
B)
wound-rotor induction motor
C)
synchronous motor
D)
d.c. shunt motor
A synchronous motor can operate at different power factors by varying its field excitation. Underexcited operation makes it draw lagging current, while overexcited operation makes it draw leading current. Hence it can conveniently operate at both lagging and leading power factor. The other motors listed are generally not used for adjustable power-factor operation: induction motors usually operate at lagging power factor, and a d.c. shunt motor is not an a.c. power-factor machine.
A negative sequence relay is commonly used to protect
A)
An alternator
B)
A transformer
C)
A transmission line
D)
A bus bar
A negative sequence relay protects an alternator (generator) because unbalanced loads or faults produce negative-sequence currents that create double-frequency currents in the rotor, causing overheating and damage. Hence it is commonly used for alternator protection. It is not primarily used for transformers, transmission lines, or bus bars.
Shunt reactors are sometimes used in high voltage transmission system to
A)
limit the short circuit current through the line.
B)
compensate for the series reactance of the line under heavily loaded condition.
C)
limit over-voltages at the load side under lightly loaded condition.
D)
compensate for the voltage drop in the line under heavily loaded condition.
Shunt reactors absorb reactive power from the system. In high-voltage transmission lines, especially under light-load or no-load conditions, line capacitance causes the Ferranti effect, leading to a rise in receiving-end voltage. A shunt reactor is connected to counteract this capacitive effect and limit over-voltages. Option (a) refers to fault current limiting, which is not the main purpose of shunt reactors. Options (b) and (d) relate to series compensation or voltage regulation under heavy load, which are functions of series capacitors/reactors or voltage control devices, not shunt reactors.
In a speed control system, output rate feedback is used to
A)
Limit the speed of motor.
B)
Limit the acceleration of the motor.
C)
Reduce the damping of the system.
D)
Increase the gain margin.
In a speed control system, output rate feedback means feedback proportional to the rate of change of output speed. This acts like derivative feedback, which opposes sudden changes and improves dynamic response. As a result, it mainly limits the acceleration of the motor. It does not directly limit the steady speed, it does not reduce damping, and gain margin is not the primary purpose of rate feedback.
Wait-for graph is used for
A)
detecting view serializability
B)
detecting conflict serializability
C)
deadlock prevention
D)
deadlock detection
A wait-for graph is a directed graph used in DBMS to represent which transaction is waiting for which other transaction. If the graph contains a cycle, it indicates a deadlock. Therefore, wait-for graphs are used for deadlock detection. It is not used for view serializability or conflict serializability, and it does not prevent deadlocks; it only helps detect them.
Coupling is a qualitative indication of the degree to which a module
A)
can be written more compactly.
B)
focuses on just one thing.
C)
is able to complete its function in a timely manner.
D)
is connected to other modules and the outside world.
Coupling measures the degree of interdependence between modules. A module with high coupling is strongly connected to other modules or external components, while low coupling is preferred in good software design. Option (d) correctly describes coupling. Option (b) refers to cohesion, not coupling.
If P is risk probability, L is loss, then Risk Exposure (RE) is computed as
A)
RE = P/L
B)
RE = P + L
C)
RE = P*L
D)
RE = 2* P *L
In software engineering risk management, Risk Exposure (RE) is calculated as the product of the probability of the risk occurring and the loss caused by it: RE = P × L. Option (a) is incorrect because division is not used, option (b) is just addition, and option (d) incorrectly doubles the standard formula.
A query in the tuple relational calculus is expressed as
A)
{t | P() | t}
B)
{P(t) | t}
C)
{t | P(t)}
D)
All of these
In tuple relational calculus, a query is written in the form { t | P(t) }, where t is a tuple variable and P(t) is a predicate that specifies the condition tuples must satisfy. Option (a) and (b) are not the standard tuple relational calculus notation, so they are incorrect. Therefore, the correct answer is (c).
A _____ is a device that forwards packets between networks by processing the routing information included in the packet.
A)
Bridge
B)
Router
C)
Firewall
D)
Switch
A router forwards packets between different networks by examining the routing information in the packet and choosing the best path. A bridge and a switch mainly forward frames within a LAN, while a firewall filters traffic based on security rules rather than routing packets between networks.
The name of the protocol which provides virtual terminal in TCP/IP model is.
A)
SMTP
B)
Telnet
C)
HTTP
D)
None of these
Telnet is the protocol that provides a virtual terminal service in the TCP/IP model, allowing a user to log in to a remote computer and interact with it as if using a local terminal. SMTP is used for email transfer, and HTTP is used for web communication. Therefore, the correct answer is Telnet.
The aim of software engineering is to produce software that is
A)
Fault-free
B)
Delivered on time, Delivered within budget
C)
Satisfies users’ needs
D)
All of these
Software engineering aims to develop software that is reliable and as fault-free as possible, delivered on time and within budget, and most importantly satisfies users’ needs. Since all three statements are valid goals, the correct answer is 'All of these'.
In SQL the statement select * from R, S is equivalent to
A)
Select * from R natural join S
B)
Select * from R cross join S
C)
Select * from R union join S
D)
Select * from R inner join S
In SQL, `SELECT * FROM R, S` lists two tables in the FROM clause without any join condition. This produces the Cartesian product of R and S, which is exactly a CROSS JOIN. A NATURAL JOIN or INNER JOIN requires matching conditions, and UNION combines rows vertically rather than forming all pairwise combinations.
__________ is a black box testing method
A)
Boundary value analysis
B)
Basic path testing
C)
Code path analysis
D)
None of these
Boundary value analysis is a black box testing technique because it tests the input/output behavior of the software without looking at the internal code. It focuses on values at the boundaries of input ranges, where defects are most likely. Basic path testing and code path analysis are white box techniques because they depend on the internal structure and logic of the program. Therefore, the correct answer is Boundary value analysis.
The main design activities in the software design process are: i) System specification, ii) interface design, iii) Component design, iv) algorithm design
A)
ii, iii and iv only
B)
i, ii and iii only
C)
i, iii and iv only
D)
All i, ii, iii and iv
In software engineering, the main design activities are interface design, component design, and algorithm design. System specification is not a design activity; it is part of requirements/specification before design begins. Therefore, the correct set is ii, iii and iv only.