← MES Jr. Grade
Past Questions — 2015
While measuring power of a 3-phase load by two-wattmeter method, the readings of the two wattmeters are equal and opposite when
A)
power factor is unity
B)
load is balanced
C)
phase angle is between 30° and 60°
D)
the load is purely inductive
In the two-wattmeter method for a 3-phase load, the wattmeter readings become equal in magnitude and opposite in sign when the power factor is zero. A purely inductive load has zero power factor, so one wattmeter reads positive and the other negative with equal magnitude. Hence the readings are equal and opposite. The other options are incorrect because unity power factor gives equal positive readings, a balanced load alone does not ensure equal and opposite readings, and a phase angle between 30° and 60° gives unequal readings.
Two incandescent light bulbs of 40 W and 60 W rating are connected in series across the mains. Then
A)
The bulbs together consume 100 W.
B)
The bulbs together consume 50 W.
C)
The 60 W bulb glows brighter.
D)
The 40 W bulb glows brighter.
For bulbs rated at the same mains voltage, resistance R = V^2/P. So the 40 W bulb has higher resistance than the 60 W bulb. In series, the same current flows through both bulbs, and power dissipated is P = I^2R. Therefore the bulb with higher resistance dissipates more power and glows brighter. Hence the 40 W bulb glows brighter. The other options are incorrect because the bulbs do not consume their rated powers in series, and the 60 W bulb has lower resistance, so it glows dimmer.
Data acquisition systems are usually of
A)
analog type
B)
digital type
C)
integrating type
D)
hybrid type
Data acquisition systems (DAS) generally handle both analog signals from sensors and digital processing/storage units. The input is often analog, then it is conditioned, sampled, and converted to digital form for processing. Because they combine analog and digital elements, DAS are usually of hybrid type. Analog type alone is incomplete, digital type alone ignores the sensor/input stage, and integrating type is not the usual classification here.
An electromagnetic field is radiated from
A)
A stationary point charge
B)
A capacitor with dc voltage
C)
A conductor carrying a dc current
D)
An oscillating dipole
Electromagnetic radiation is produced by accelerating charges or time-varying currents and fields. An oscillating dipole has charges moving back and forth, so it continuously creates changing electric and magnetic fields that propagate outward as radiation. A stationary point charge does not radiate, a capacitor with dc voltage produces a static electric field, and a conductor carrying dc current produces a steady magnetic field, not radiation.
R.M.S. value & mean value both are the same in case of
A)
Square wave
B)
Triangular wave
C)
Sine wave
D)
Rectangular wave
For a symmetrical square wave, the waveform has a constant magnitude throughout each half-cycle. Hence its RMS value equals its average (mean) value over a cycle. In contrast, for a sine wave the RMS and mean values are different, and for a triangular wave they are also different. Therefore, the correct answer is Square wave.
Dissipation factor, tan δ, of a capacitor is measured by which bridge?
A)
Anderson bridge
B)
Hay bridge
C)
Schering bridge
D)
Wien bridge
The dissipation factor (tan δ) of a capacitor is measured using the Schering bridge. This bridge is specifically designed for testing insulating materials and capacitors, and it can determine capacitance, dielectric loss, and dissipation factor. Anderson bridge and Hay bridge are used for measuring inductance, while Wien bridge is mainly used for frequency measurement and oscillator circuits.
Which of the following defects is responsible for creeping in an induction type energy meter?
A)
Imperfect lag compression
B)
Over friction compensation
C)
Imperfect overload compensation
D)
Misalignment of brake magnet
Creeping in an induction type energy meter is the slow continuous rotation of the disc at no load. It is commonly caused by excessive or over-compensation of friction, which makes the disc move even when there is negligible load. Hence, the defect responsible for creeping is **over friction compensation**. The other options relate to different meter adjustments or defects, not the usual cause of creeping.
A 3-phase 3-wire supply feeds a star connected load consisting of 3 equal resistors. If one of the resistors is to be removed, then what is the reduction in power as compared to the original power?
A)
25% of the original power
B)
33.3% of the original power
C)
50% of the original power
D)
66.66% of the original power
For a balanced star-connected load with three equal resistors, the original total power is proportional to the sum of power in all three phases. If one resistor is removed, only two identical phase resistors remain connected, so the new power becomes 2/3 of the original. Therefore, the reduction in power is 1/3 of the original, i.e. 33.3%. Hence, the correct option is (b).
An air gap is usually inserted in magnetic circuits to
A)
increase the flux
B)
prevent saturation
C)
increase the mmf
D)
none of these
An air gap is inserted in a magnetic circuit mainly to increase the reluctance of the circuit and thereby limit the flux. This helps prevent the magnetic core from reaching saturation. Option (a) is incorrect because an air gap does not increase flux; it usually reduces it for a given mmf. Option (c) is incorrect because mmf is not increased by the air gap; rather, more mmf is required to produce the same flux. Hence, the correct answer is (b) prevent saturation.
Which of the following are data representation elements in a generalised measurement system?
A)
Analog indicator
B)
Amplifier
C)
A/D converter
D)
Digital display
In a generalized measurement system, the data representation stage presents the measured information to the user. A digital display is a direct data representation element. An analog indicator can also represent data, but in standard measurement-system block classification, the output/data representation element among the given options is the digital display. An amplifier is a signal-conditioning element, and an A/D converter is a data conversion element, not a representation element.
A material that does not allow current it under normal conditions is a(n)
A)
insulator
B)
conductor
C)
semiconductor
D)
valence
A material that does not allow electric current to pass through it under normal conditions is called an insulator. Conductors allow current easily, semiconductors allow current only under certain conditions, and valence is not a type of material.
Power factor of a resonant circuit is
A)
1
B)
0
C)
infinite
D)
depends on the values of the circuit parameters
In a resonant circuit, the inductive and capacitive reactances cancel each other, so the net reactance becomes zero. Therefore the circuit behaves as a purely resistive circuit, and voltage and current are in phase. Hence the power factor is unity, i.e., 1. Option (b) is incorrect because power factor is not zero at resonance; option (c) is incorrect because infinite is not the power factor; option (d) is incorrect because at resonance the power factor is fixed at 1.
Which of the following exhibits hysteresis?
A)
Ferromagnetic materials only
B)
Ferroelectric materials only
C)
Ferrielectric materials only
D)
Both ferromagnetic and ferroelectric materials
Hysteresis is the lagging response of a material when the applied field is cycled. Ferromagnetic materials show a magnetic hysteresis loop (magnetization vs. magnetic field), and ferroelectric materials show an electric hysteresis loop (polarization vs. electric field). Therefore, both exhibit hysteresis. Options (a) and (b) are incomplete because each mentions only one class, and (c) is not the standard correct category here.
The conductivity of a metal is determined by
A)
the number of valence electrons per atom
B)
the electron concentration and the mobility of the free electrons
C)
both (a) and (b)
D)
none of these
The electrical conductivity of a metal depends on how many free electrons are available to carry charge and how easily they move through the lattice. In formula form, conductivity is proportional to electron concentration × mobility. Option (a) is not sufficient by itself, because the number of valence electrons does not directly determine conductivity unless their concentration and mobility are considered. Therefore, (b) is correct.
The precision of a ramp type digital voltmeter depends on
A)
frequency of the generator and slope of the ramp
B)
frequency of the generator
C)
slope of the ramp
D)
switching time of the gate
In a ramp-type digital voltmeter, the input voltage is measured by comparing it with a linearly changing ramp voltage. The accuracy/precision mainly depends on how stable and linear the ramp slope is, because any variation in slope directly affects the time measurement and hence the voltage reading. The generator frequency is not the governing factor here, and gate switching time is not the primary determinant of precision.
Which of the following is the poorest electrical conductor?
A)
steel
B)
carbon
C)
copper
D)
aluminium
Among the given materials, copper and aluminium are good electrical conductors, carbon conducts electricity better than steel in many forms (especially graphite), while steel has much higher electrical resistivity than the others. Therefore, steel is the poorest electrical conductor in the list.
Kelvin double bridge is chosen to measure low resistance because
A)
it has high sensitivity
B)
thermoelectric emf’s can be taken
C)
resistance variation due to temperature can be accounted for
D)
resistance variation due of contacts and leads can be eliminated
Kelvin double bridge is used for measuring very low resistances because the effect of lead and contact resistances becomes significant at low values. The bridge uses a four-terminal arrangement and a ratio-arm compensation method to eliminate the error caused by the resistance of connecting leads and contacts. Hence, option (d) is correct. Option (a) is not the main reason, (b) is unrelated, and (c) is not the principle of Kelvin double bridge.
How can the power supplied to a high frequency heating system be measured?
A)
By dynamometer wattmeter
B)
By induction wattmeter
C)
By thermocouple type wattmeter
D)
By moving iron ammeter and voltmeter
In high-frequency heating systems, ordinary wattmeters are unsuitable because their coils and moving systems cannot respond accurately at high frequencies. A thermocouple type wattmeter is used because it measures true power over a wide frequency range, including high frequencies. Dynamometer wattmeters are mainly for low-frequency AC/DC measurements, induction wattmeters work only on AC at power frequency, and moving iron ammeter/voltmeter measure current and voltage separately, not power directly.
A circuit component that opposes the change in circuit voltage is
A)
resistance
B)
capacitance
C)
inductance
D)
all of these
A capacitor opposes sudden change in voltage because the voltage across a capacitor cannot change instantaneously. In contrast, an inductor opposes change in current, and resistance opposes current flow in general. Therefore, the correct answer is capacitance.
Four amperes of current are measured through a 24 Ω resistor connected across a voltage source. How much voltage does the source produce?
A)
960 V
B)
9.6V
C)
96V
D)
8V
Use Ohm’s law: V = IR. Here, current I = 4 A and resistance R = 24 Ω. So, V = 4 × 24 = 96 V. Therefore, the correct option is (c) 96V. The other options are incorrect because they do not satisfy Ohm’s law for the given current and resistance.
Which of the following materials can be used for permanent magnets?
A)
Alnico
B)
Barium ferrite
C)
Carbon steel
D)
Iron-cobalt alloy
Permanent magnets require materials with high retentivity and coercivity so that they retain magnetism for a long time. Alnico (an alloy of aluminium, nickel, and cobalt, often with iron and copper) is a well-known permanent magnet material. Barium ferrite is also used for permanent magnets, but in standard single-correct MCQs like this, Alnico is the expected answer. Carbon steel is not preferred for permanent magnets because it loses magnetism more easily. Iron-cobalt alloys are mainly used where high magnetic saturation is needed, not as the usual answer for permanent magnets in such questions.
ALNICO is an alloy of?
A)
iron, aluminum
B)
aluminum, nickel
C)
iron, cobalt, nickel
D)
aluminum, nickel, iron and cobalt
Alnico is a family of permanent magnet alloys made mainly from aluminum (Al), nickel (Ni), and cobalt (Co), with iron (Fe) as the major base metal. Hence the correct composition among the options is aluminum, nickel, iron and cobalt. Option (a) is incomplete, (b) omits iron and cobalt, and (c) misses aluminum.
Which of the following instruments is commonly used to measure primary current of a transformer connected to mains?
A)
Electrostatic meter
B)
Current transformer
C)
Moving coil type meter
D)
Moving iron meter
The primary current of a transformer connected to mains is usually measured using a current transformer (CT). A CT steps down the large current to a smaller, proportional value that can be safely measured by an ammeter or meter. Electrostatic meters are used for high-voltage measurements, moving coil meters are mainly for DC, and moving iron meters are used for AC measurements but not specifically for directly measuring large primary currents in transformer circuits.
With the increase in temperature, the insulating property of insulator
A)
weakens
B)
gains
C)
remains same
D)
none of these
In an insulator, increasing temperature gives more thermal energy to electrons, so some electrons can move to the conduction band. As a result, conductivity increases and the insulating property decreases. Therefore, the insulating property weakens with rise in temperature. Options (b) and (c) are incorrect because insulation does not improve or remain unchanged; (d) is unnecessary since (a) is correct.
If R, L and C are parameters of a resistor, what is the condition for the resistor to be non-inductive?
A)
L=CR
B)
L=CR²
C)
C=LR²
D)
C=R/L
For a resistor to be non-inductive, its inductive reactance must be cancelled by the effect of the distributed capacitance. The standard condition for a non-inductive resistance winding is L = CR², where L is inductance, C is capacitance, and R is resistance. Hence option (b) is correct. The other options do not represent the known non-inductive condition.