← MES Jr. Grade
Past Questions
The lissajous pattern appearing on the screen of a CRT, when two sinusoidal voltages of equal frequencies, which are in phase with each other are applied to the CRO is
A)
a straight line
B)
a circle
C)
an ellipse
D)
a parabola
When two sinusoidal voltages of equal frequency and zero phase difference are applied to the X and Y inputs of a CRO, the Lissajous figure is a straight line. This is because both voltages rise and fall together, so the spot moves along one diagonal line. A circle or ellipse occurs when there is a phase difference, and a parabola is not the Lissajous pattern for equal-frequency sinusoids.
Input gate current of a FET is
A)
a few microampere
B)
negligibly small
C)
a few milliamperes
D)
a few amperes
In a FET, the gate is reverse-biased (in JFET) or insulated by an oxide layer (in MOSFET), so the gate current is ideally zero and practically negligibly small. Hence option (b) is correct. The other options are too large for a FET gate current.
Magnetic recording tape is most commonly made from
A)
small particles of iron
B)
silicon iron
C)
ferric oxide
D)
ferrous oxide
Magnetic recording tapes are commonly coated with fine particles of ferric oxide (Fe2O3), which can retain magnetization and store audio/video signals. Silicon iron is used in transformer cores, not tapes. Ferrous oxide is not the standard magnetic coating material, and small particles of iron are not the usual commercial tape medium.
A TTT diagram is useful for predicting the transformation behaviour of
A)
ferrite
B)
austenite
C)
martensite
D)
pearlite
A TTT (Time-Temperature-Transformation) diagram shows how austenite transforms into different microstructures such as pearlite, bainite, or martensite at various temperatures and times. It is therefore used to predict the transformation behaviour of austenite. Ferrite, pearlite, and martensite are products of transformation, not the phase whose transformation is being tracked in the TTT diagram.
The input impedance of a CRO is about
A)
zero
B)
10Ω
C)
100Ω
D)
1MΩ
A CRO (Cathode Ray Oscilloscope) is designed to measure signals without significantly loading the circuit, so its input impedance is very high. The standard input impedance is about 1 MΩ, often with a small parallel capacitance. Hence, option (d) is correct. Options (a), (b), and (c) are far too low and would heavily load the circuit.
In an unbiased P-N junction, thickness of depletion layer is of the order of
A)
0.005µm
B)
0.5 µm
C)
5 µm
D)
1nm
In an unbiased P-N junction, the depletion region is typically of the order of a fraction of a micrometre. A common approximate value is about 0.5 µm. Option (a) 0.005 µm and (d) 1 nm are too small, while (c) 5 µm is generally too large for an unbiased junction.
A digital voltmeter has a readout range from 0 to 999 counts. If the full scale reading is 9.999V, the resolution is
A)
1V
B)
10mV
C)
1mV
D)
0.001mV
A digital voltmeter with a readout of 0 to 999 counts and a full-scale reading of 9.999 V has 1000 possible display steps. So the least significant digit corresponds to 9.999 V / 999 ≈ 0.01 V? But in standard DVM notation, 9.999 V means the smallest increment is 0.001 V = 1 mV. Hence the resolution is 1 mV. The other options are too coarse or too fine.
RTD is generally suitable for temperature of about
A)
50ºC
B)
200º C
C)
800ºC
D)
1500º C
RTD (Resistance Temperature Detector) is generally used for moderate temperature measurement, typically up to about 200°C to 600°C depending on the material and design. Among the given options, 200°C is the most suitable and standard answer. 50°C is too low to be a defining upper limit, while 800°C and 1500°C are far beyond the normal operating range of RTDs.
The unit of electrical conductivity is
A)
mho/meter
B)
mho/m2
C)
ohm/m
D)
ohm/m2
Electrical conductivity is the reciprocal of resistivity. Since resistivity has unit ohm-meter (Ω·m), conductivity has unit 1/(Ω·m), which is commonly written as mho per meter (or siemens per meter). Therefore, option (a) is correct. Options (c) and (d) are units related to resistance/resistivity, not conductivity.
The turn on voltage of a Ge junction diode is
A)
0.1 V
B)
0.3 V
C)
0.7V
D)
1.0 V
A germanium (Ge) junction diode has a low barrier potential, so its turn-on (cut-in) voltage is about 0.3 V. By comparison, a silicon diode is about 0.7 V. Hence option (b) is correct, while 0.1 V is too low and 0.7 V/1.0 V are typical of silicon or higher-voltage devices.
The permeability and permittivity of a medium are
A)
independent of each other
B)
related by the velocity of electromagnetic wave
C)
related by the Boltzmann’s constant
D)
None of the above
For an electromagnetic wave in a medium, the wave speed is given by v = 1 / √(μϵ), where μ is permeability and ϵ is permittivity. Hence, permeability and permittivity are related through the velocity of the electromagnetic wave. Option (a) is incorrect because they are not independent in this context, and option (c) is unrelated.
the signal to noise ratio in telemetry should be
A)
5 dB
B)
10 dB
C)
25 dB
D)
60 dB
In telemetry systems, the signal-to-noise ratio should be very high to ensure reliable transmission and accurate reception of measured data. Among the given options, 60 dB is the most appropriate and standard desirable value. Lower values like 5 dB, 10 dB, or even 25 dB indicate comparatively poor noise immunity and are not suitable for telemetry.
Which of the following is not a piezo-electric material?
A)
Rochell salt
B)
quartz
C)
lithium sulphate
D)
sodium-bicarbonate
Rochelle salt, quartz, and lithium sulphate are well-known piezo-electric materials. Sodium bicarbonate is not used as a piezo-electric material. Therefore, the correct answer is sodium-bicarbonate.
The temperature at which a material becomes a glassy solid is called
A)
melting temperature
B)
recrystallization temperature
C)
glass transition temperature
D)
freezing temperature
The temperature at which an amorphous material changes from a rubbery or viscous state into a hard, glassy solid is called the glass transition temperature (Tg). This is different from melting temperature, which applies to crystalline solids. Recrystallization temperature is related to crystal formation, and freezing temperature is the liquid-to-solid change point for ordinary substances, not the specific glassy transition.
In a JFET operating above pinch-off voltage, the
A)
drain current increases steeply
B)
drain current remains constant
C)
drain current starts decreasing
D)
depletion region become smaller
In a JFET, when the drain-source voltage is increased beyond the pinch-off voltage, the channel is pinched off near the drain end and the drain current enters the saturation region. In this region, the drain current remains almost constant, with only a slight increase due to channel-length modulation. Hence, the correct option is (b). Option (a) is wrong because current does not rise steeply after pinch-off. Option (c) is wrong because the current does not start decreasing in normal operation. Option (d) is wrong because the depletion region does not become smaller; it actually extends further as reverse bias increases.
Which semiconductor device acts like a diode and two resistors?
A)
SCR
B)
triac
C)
diac
D)
UJT
A UJT (Unijunction Transistor) is often described as behaving like a diode with two resistors because its equivalent structure can be modeled as a resistive silicon bar with a PN junction emitter. This gives it diode-like triggering characteristics along with two resistive sections. SCR, triac, and diac are different thyristor devices and are not commonly described this way.
Vulcanized rubber
A)
Is produced from trans-polyisoprene
B)
Is alternatively known as neoprene
C)
Contains about 20% sulphur by weight
D)
Is produced from cis-polyisoprene
Vulcanized rubber is made from natural rubber, which is cis-1,4-polyisoprene. Vulcanization is the process of heating rubber with sulphur to improve its strength and elasticity, but the base polymer remains cis-polyisoprene. Option (a) is wrong because trans-polyisoprene is gutta-percha, not natural rubber. Option (b) is wrong because neoprene is a different synthetic rubber. Option (c) is wrong because vulcanized rubber does not contain about 20% sulphur; typical sulphur content is much lower.
It is required to measure temperature in the range of 1300º–1520ºC. The most suitable thermo couple is
A)
chromel- constantan
B)
iron-constantan
C)
chromel-alumel
D)
platinum-rhodium
For very high temperatures like 1300°C to 1520°C, a noble-metal thermocouple is required. Platinum-rhodium thermocouples are suitable for this range because they can withstand high temperatures and provide stable, accurate measurements. Chromel-constantan and iron-constantan are used for much lower temperature ranges, while chromel-alumel is generally suitable up to about 1200°C, which is below the required range.
Which of the following does not constitute a point defect in crystal?
A)
self interstitials
B)
substitutional atoms
C)
slip lines
D)
vacancies
Point defects are localized imperfections involving one or a few atoms, such as vacancies, self-interstitials, and substitutional atoms. Slip lines are not point defects; they are surface manifestations of plastic deformation caused by dislocation motion, so they are line/planar defect-related rather than point defects.
Ionic bonding in solids depends primarily on
A)
Van der Waals forces
B)
electrical dipoles
C)
sharing of electrons
D)
transfer of electrons
Ionic bonding is formed when one atom transfers one or more electrons to another atom, creating oppositely charged ions that attract each other electrostatically. Hence, it depends primarily on transfer of electrons. Van der Waals forces are weak intermolecular forces, electrical dipoles relate to polar molecules, and sharing of electrons describes covalent bonding.
The time base signal in a CRO is
A)
a sinusoidal signal
B)
square wave signal
C)
saw tooth signal
D)
triangular wave signal
In a CRO, the time base (sweep) circuit must move the electron beam horizontally at a constant speed and then return it rapidly to the starting point. This is achieved by a sawtooth waveform: a linear rise for uniform horizontal motion, followed by a quick fall for retrace. A sinusoidal or triangular wave would not provide the required rapid retrace, and a square wave is not suitable for linear sweep.
Which method can be used for absolute measurement of resistance?
A)
Ohm’s Law method
B)
Wheatstone bridge method
C)
Raleigh method
D)
Lorentz method
Absolute measurement of resistance is commonly done using the Wheatstone bridge method because it compares an unknown resistance with known resistances and gives high accuracy. Ohm’s law method is a direct method but not as accurate for absolute measurement. Raleigh method and Lorentz method are not standard methods for absolute resistance measurement in basic instrumentation.
The mass of a proton is roughly how many times the mass of an electron?
A)
184,000
B)
18,400
C)
1,840
D)
184
The proton is much heavier than the electron. Its mass is about 1836 times the mass of an electron, which is commonly rounded to 1840 in exam questions. Therefore, option (c) is correct. The other options are far too large or too small.
Which bridge can be used to measure frequency?
A)
Maxwell
B)
Kelvin
C)
Schering
D)
Wien
The Wien bridge is used to measure frequency, especially in audio-frequency ranges. It is a frequency-sensitive bridge whose balance condition depends on frequency. Maxwell bridge is used for measuring inductance, Kelvin bridge for low resistance, and Schering bridge for capacitance and dielectric loss.
An insulator is one whose
A)
valence band is empty
B)
conduction band is full
C)
energy gap between the two band is large
D)
none of these
An insulator is characterized by a very large forbidden energy gap between the valence band and the conduction band. Because of this large gap, electrons cannot easily move to the conduction band, so current does not flow readily. Option (a) is incorrect because the valence band in an insulator is generally full, not empty. Option (b) is incorrect because a full conduction band does not define an insulator; in fact, conduction depends on available empty states and band gap. Hence, (c) is correct.