← MES Jr. Grade
Past Questions
If the bandwidth of an oscilloscope is given as direct current to 10 MHz, what is the fastest rise time a sine wave can have to be produced accurately by the oscilloscope?
A)
35 ns
B)
10 ns
C)
3.5 ns
D)
0.035 ns
For an oscilloscope, the approximate relationship between bandwidth and rise time is t_r 0.35 / BW. Here BW = 10 MHz, so t_r = 0.35 / (10 00d7 10^6) = 35 d7 10^-9 s = 35 ns. Therefore, the fastest rise time that can be reproduced accurately is 35 ns. The other options do not match the standard bandwidth-rise time relation.
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.
Unit of electric intensity is :
A)
joules/coulomb
B)
newton/coulomb
C)
volt/meter
D)
both (b) and (c)
Electric intensity means electric field intensity. Its SI unit can be written as newton per coulomb (N/C) or equivalently volt per meter (V/m). Since both units are correct and equivalent, the correct option is (d). Option (a) joule/coulomb is the unit of electric potential, not electric intensity.
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.
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.
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.
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.
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.
Pure metals generally have
A)
high conductivity and low temperature coefficient
B)
high conductivity and high temperature coefficient
C)
low conductivity and zero temperature coefficient
D)
low conductivity and high temperature coefficient
Pure metals generally have many free electrons, so they conduct electricity well. As temperature increases, lattice vibrations increase and electron scattering becomes greater, so their resistance rises noticeably. Hence pure metals have high conductivity and a high temperature coefficient of resistance. Option (a) is wrong because pure metals do not have a low temperature coefficient; option (c) is wrong because conductivity is not low and the temperature coefficient is not zero; option (d) is wrong because conductivity is not low.
Which of the following is correct? As frequency increases, the surface resistance of a metal
A)
Decreases
B)
Increases
C)
Remains unchanged
D)
Varies in an unpredictable manner
For a metal, as frequency increases, the skin effect becomes stronger. Current tends to flow only near the surface, reducing the effective conducting area. Hence the surface resistance increases with frequency. Therefore, option (b) is correct. Options (a), (c), and (d) are incorrect because the resistance does not decrease, remain constant, or vary randomly; it rises systematically with frequency.
A moving coil galvanometer is made into a dc ammeter by connecting
A)
a low resistance across the meter
B)
a high resistance in series with meter
C)
a pure inductance across the meter
D)
a capacitor in series with the meter
A moving coil galvanometer is converted into a DC ammeter by connecting a low resistance shunt in parallel across the meter. The shunt carries most of the current, while only a small fraction passes through the galvanometer. This allows the instrument to measure larger currents without damaging the coil. A high resistance in series is used to convert a galvanometer into a voltmeter, not an ammeter. A pure inductance or a capacitor is not used for DC current measurement.
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.
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 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.
Schering bridge can be used to measure which one of the following?
A)
Q of a coil
B)
Inductance and its Q-value
C)
Very small resistance
D)
Capacitance and its power factor
A Schering bridge is an AC bridge used primarily for measuring an unknown capacitance and the dielectric loss (often expressed as power factor) of a capacitor. It is not mainly used for measuring inductance or resistance. Therefore, the correct option is (d).
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.
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.
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.
The errors introduced by an instrument fall in which category?
A)
Systematic errors
B)
Random errors
C)
Gross errors
D)
Environmental errors
Errors introduced by an instrument are generally due to imperfections in the instrument itself, such as calibration error, zero error, or drift. These are classified as systematic errors because they produce a consistent bias in the measurements. Random errors vary unpredictably, gross errors are human mistakes, and environmental errors are caused by external conditions like temperature or humidity.
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.
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.
Line insulators are made of
A)
porcelain
B)
mica
C)
marble
D)
pve
Line insulators used on overhead transmission and distribution lines are commonly made of porcelain because it has high dielectric strength, good mechanical strength, and withstands weathering. Mica is used in electrical insulation applications but not as line insulators. Marble is not used for this purpose. 'pve' is not a standard insulating material for line insulators.
Which one of the following bridges is used for measurement of dielectric loss and power factor of a capacitor?
A)
Maxwell’s bridge
B)
Anderson bridge
C)
De Sautty’s bridge
D)
Schering bridge
The Schering bridge is specifically used to measure the capacitance, dielectric loss, and power factor of a capacitor. Maxwell’s bridge and Anderson bridge are mainly used for inductance measurement, while De Sautty’s bridge is used for comparing capacitances, not for dielectric loss and power factor measurement.
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.
Hali’s effect is used to measure
A)
electric field intensity
B)
magnetic field intensity
C)
carrier concentration
D)
none of these
Hall effect is the development of a transverse voltage across a current-carrying conductor or semiconductor when it is placed in a magnetic field. This Hall voltage is used to measure magnetic field intensity. It is not used to measure electric field intensity directly, and while it can help determine carrier concentration in semiconductors, the standard direct application asked here is magnetic field measurement.