← MES Jr. Grade
Past Questions
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.
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.
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.
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.
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.
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.
Which of the following is a frequency sensitive bridge?
A)
De-sauty bridge
B)
Schering bridge
C)
Wien’s bridge
D)
Maxwell’s bridge
A frequency-sensitive bridge is one whose balance condition depends on frequency. Wien’s bridge is used for frequency measurement and its balance equation includes frequency, so it is frequency sensitive. De-Sauty bridge, Schering bridge, and Maxwell’s bridge are mainly used for measuring capacitance, dielectric loss, and inductance respectively, and are not primarily frequency-sensitive in this sense.
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.
Frequency can be measured by using
A)
Maxwell’s bridge
B)
Schering bridge
C)
Heaviside Campbell bridge
D)
Wien’s bridge
Frequency can be measured using the Heaviside-Campbell bridge, which is specifically used for determining frequency (or frequency-related quantities) in AC bridge circuits. Maxwell’s bridge is used for inductance measurement, Schering bridge for capacitance and dielectric loss, and Wien’s bridge is commonly used for frequency measurement in oscillators, not as the standard bridge answer here in measurements theory. Hence, the correct option is (c) Heaviside Campbell bridge.
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 digital voltmeter measures
A)
Peak value
B)
Peak to peak value
C)
Rms value
D)
Average value
A digital voltmeter (DVM) is generally calibrated to display the effective value of AC voltage, i.e., the RMS value. RMS is the standard measure of AC magnitude because it represents the equivalent DC heating effect. Peak, peak-to-peak, and average values are not the usual direct indication of a DVM.
The materials in which valence electrons are bounded very tightly to their parent atoms are called
A)
ferrites
B)
super conductors
C)
insulators
D)
none of these
In insulators, valence electrons are tightly bound to their parent atoms, so they cannot move freely and therefore do not conduct electricity well. Ferrites are magnetic ceramic materials, and superconductors allow current to flow with zero resistance under certain conditions. Hence, the correct answer is insulators.
Superconducting metal in superconducting state has relative permeability of
A)
More than one
B)
One
C)
Zero
D)
Negative
A superconductor in the superconducting state exhibits the Meissner effect, meaning it expels magnetic flux from its interior. Hence its magnetic susceptibility is strongly diamagnetic and the relative permeability becomes approximately 0. Therefore, the correct answer is Zero. Option (b) one is for ordinary non-magnetic materials, while (a) and (d) are not correct for superconductors.
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.
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.
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.
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.
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.
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.
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.
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.
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.
Fermi level in a p type semiconductor lies close to which one of the following?
A)
The top of the valence band
B)
The bottom of the valence band
C)
The top of the conduction band
D)
The bottom of the conduction band
In a p-type semiconductor, acceptor impurities create more holes, so the Fermi level shifts downward and lies closer to the valence band. Therefore, it is nearest to the top of the valence band. The conduction band options are incorrect because the Fermi level in p-type material moves away from the conduction band.
When the temperature of a magnetic material is raised above the Curie point, it becomes
A)
Diamagnetic
B)
Paramagnetic
C)
Ferromagnetic
D)
Ferrimagnetic
Above the Curie point, a ferromagnetic material loses its spontaneous magnetization because thermal agitation overcomes the alignment of magnetic domains. It no longer remains ferromagnetic and behaves as a paramagnetic substance. Diamagnetic and ferrimagnetic are not the correct general behavior above the Curie temperature.