← MES Jr. Grade
Past Questions
At higher forward voltages, a junction diode is likely to
A)
burnout
B)
get saturated
C)
suffer breakdown
D)
become noisy
At higher forward voltages, a junction diode conducts a very large current. This excessive current causes overheating and can damage the diode, leading to burnout.
Why others are incorrect:
- (b) get saturated: saturation is not the usual failure mode of a forward-biased diode.
- (c) suffer breakdown: breakdown is typically associated with reverse bias, not forward bias.
- (d) become noisy: noise may occur in electronic devices, but it is not the primary effect of excessive forward voltage in a diode.
Find the wrong statement: specific heat of a material is
A)
constant
B)
heat capacity per unit mass
C)
extrinsic property
D)
of units as Joule/Kg-K
Specific heat (specific heat capacity) is the heat capacity per unit mass, with SI unit J/kg-K. It is an intensive property, not an extrinsic property. Therefore, option (c) is the wrong statement. Options (b) and (d) are correct. Option (a) is generally taken as true in basic exam context for a given material over a limited temperature range.
Which of the following expression states Gibb’s phase rule?
A)
F = C-P+1
B)
F = C-P+2
C)
F = C-P+3
D)
F = C+P-3
Gibbs’ phase rule for a non-reacting system is F = C - P + 2, where F is degrees of freedom, C is number of components, and P is number of phases. Option (a) is the reduced phase rule for condensed systems, not the general Gibbs phase rule. Options (c) and (d) are incorrect forms.
Shaft encoder is used to measure
A)
angular position
B)
linear position
C)
linear velocity
D)
angular velocity
A shaft encoder converts the rotational movement of a shaft into electrical signals, which are used to determine the shaft’s angular position. Incremental encoders can also be used to infer speed, but the primary measurement is position. Hence, the correct answer is angular position. The other options are incorrect because linear position and linear velocity are not measured directly by a shaft encoder, and angular velocity is only derived from changes in position over time.
Load cells use
A)
piezo electric effect
B)
capacitor
C)
mutual inductance
D)
strain gauge
Load cells are transducers used to measure force or weight. The most common type of load cell works on the strain gauge principle: when a load is applied, the metal element deforms slightly, changing the resistance of bonded strain gauges. This resistance change is converted into an electrical signal. Piezoelectric effect is used in dynamic force/pressure measurement, capacitors in capacitive sensors, and mutual inductance in devices like LVDTs, not standard load cells.
For converting intrinsic semiconductor into N type extrinsic semiconductor, which of the following doping element will not be suitable?
A)
arsenic
B)
antimony
C)
indium
D)
phosphorous
To convert an intrinsic semiconductor into an N-type extrinsic semiconductor, we need to dope it with a pentavalent donor impurity such as arsenic, antimony, or phosphorous. These elements contribute extra electrons, making electrons the majority carriers. Indium is trivalent, so it acts as an acceptor impurity and produces P-type semiconductor instead. Therefore, indium is not suitable for making N-type semiconductor.
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.
A resistance strain gauge has a resistance of
A)
100Ω
B)
25Ω
C)
10Ω
D)
1Ω
A resistance strain gauge typically has a nominal resistance of 120 Ω or 100 Ω in common practical use. Among the given options, 100 Ω is the standard and most appropriate value. The other values are too low for usual strain gauge applications.
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.
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.
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 peak inverse voltage is applied across a diode when it is
A)
on
B)
on a heat sink
C)
reverse biased
D)
forward biased
Peak inverse voltage (PIV) is the maximum reverse voltage a diode can withstand without breakdown. Therefore, it is applied when the diode is reverse biased. In forward bias, the diode conducts and the reverse voltage condition does not occur. Options (a), (b), and (d) do not describe the reverse-bias condition relevant to PIV.
Which of the following terms is not associated with a S/H circuit?
A)
conversion time
B)
acquisition time
C)
aperture time
D)
sample time
A sample-and-hold (S/H) circuit is associated with sampling-related terms such as acquisition time, aperture time, and sample time. These describe how the input is captured and held. Conversion time, however, belongs to the ADC process after sampling, not to the S/H circuit itself. Hence, it is the term not associated with a S/H circuit.
For enhancement only mode N-channel MOSFET polarity of Vgs is
A)
–ve
B)
+ve
C)
zero
D)
variable
In an enhancement-mode N-channel MOSFET, a positive gate-to-source voltage (Vgs) is required to induce an inversion layer and form the conducting channel. Hence the polarity of Vgs is positive. Option (a) is wrong because negative Vgs would further deplete the channel, option (c) is wrong because zero Vgs does not turn it on, and option (d) is incorrect because the required polarity is not variable.
Stainless steel are alloys of
A)
iron and nickel
B)
iron, chromium and nickel
C)
iron, chromium and molybdenum
D)
none of these
Stainless steel is primarily an alloy of iron with chromium, and often nickel is added to improve corrosion resistance and toughness. Among the given options, the standard composition matches option (b). Option (a) is incomplete because stainless steel must contain chromium; option (c) is a type of alloy steel but not the usual general definition of stainless steel; option (d) is incorrect.
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.
In an ideal Op-Amp the voltage gain for the common mode signal is
A)
zero
B)
0.5
C)
2.0
D)
∞
In an ideal op-amp, the common-mode gain is zero, meaning it does not amplify signals that are common to both inputs. This is one of the defining ideal properties of an op-amp, along with infinite open-loop gain and infinite input impedance. Therefore, the voltage gain for the common mode signal is zero. The other options are incorrect because 0.5 and 2.0 are finite gains, and ∞ refers to the differential/open-loop gain, not common-mode gain.
The crystal structure of most of the common metal is
A)
hexagonal
B)
cubic
C)
orthogonal
D)
none of these
Most common metals crystallize in cubic structures, mainly body-centered cubic (BCC) and face-centered cubic (FCC). These structures are widely found in metals like iron, copper, aluminum, and nickel. Hexagonal close-packed is also seen in some metals, but it is less common overall. Orthogonal is not the usual crystal structure for common metals.
The depletion region of a P-N junction is one that is depleted of
A)
atoms
B)
mobile charges
C)
electrons
D)
immobile charges
In a P-N junction, the depletion region is formed near the junction where electrons and holes diffuse and recombine. This leaves behind only fixed ions, so the region becomes depleted of mobile charge carriers. Hence, it is depleted of mobile charges, not atoms or immobile charges.
The number comparators needed in parallel conversion type 8-bit ADC is
A)
8
B)
16
C)
255
D)
256
In a parallel conversion (flash) 8-bit ADC, the number of comparators required is 2^n - 1, where n is the number of bits. For n = 8, this gives 2^8 - 1 = 255 comparators. However, the question asks for the number of comparators needed in parallel conversion type 8-bit ADC, and the standard flash ADC formula applies. Since the options do not include 255 as the expected flash-ADC answer, the question is likely intended for a simpler interpretation used in some exam keys, but technically the correct flash ADC requirement is 255. Therefore, among the given options, none matches the standard formula exactly.
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.
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 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.
If current through the coil of a electromagnet is doubled, then the magnetic field around the coil is
A)
halved
B)
doubled
C)
four folded
D)
same
For an electromagnet coil, the magnetic field strength is directly proportional to the current flowing through the coil (B ∝ I), assuming the number of turns and core remain the same. So, if the current is doubled, the magnetic field also doubles. Hence, option (b) is correct. The other options are incorrect because the field does not become half, four times, or remain unchanged when current is doubled.
The four stripes of a resistor are yellow-violet-orange-gold. The value of the resistance should be
A)
470Ω ± 5%
B)
47KΩ ± 5%
C)
47MΩ ± 5%
D)
47KΩ ± 10%
For a 4-band resistor, the first two bands give the significant digits, the third band is the multiplier, and the fourth band is the tolerance. Yellow = 4, Violet = 7, Orange = ×10^3, and Gold = ±5%. So the resistance is 47 × 10^3 ohms = 47 kΩ with ±5% tolerance. Hence, option (b) is correct. Option (a) would correspond to 470 Ω, which is not correct here; option (c) is too large; option (d) has the wrong tolerance.