← MES Jr. Grade
Past Questions — 2012
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.
To increase the Q factor of a coil, the wire should be
A)
long
B)
thin
C)
thick
D)
long & thin
The Q factor of a coil is inversely related to its resistance. Using a thicker wire reduces the resistance of the coil, thereby increasing the Q factor. A thin wire has higher resistance, so it lowers Q. Hence, the correct answer is thick.
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.
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.
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.
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.
A digital frequency counter can be converted to DVM by addition of a suitable
A)
VCO
B)
D/A converter
C)
power amplifier
D)
Op-Amp
A digital frequency counter measures frequency by counting pulses. To convert it into a digital voltmeter (DVM), the input voltage is first converted into a proportional frequency using a voltage-to-frequency converter, typically a VCO. The counter then measures this frequency and displays the corresponding voltage. A D/A converter, power amplifier, or op-amp alone cannot perform this conversion.
Dislocations in material are
A)
point defect
B)
line defect
C)
planner defect
D)
frenkel defect
Dislocations are defects in a crystal lattice that extend along a line, so they are classified as line defects. Point defects affect a single lattice point, planar defects occur over a plane, and Frenkel defect is a specific type of point defect.
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.
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.
Materials which can store electrical energy are called
A)
magnetic materials
B)
semi-conductors
C)
dielectric materials
D)
super conductors
Materials that can store electrical energy in an electric field are called dielectric materials. They become polarized when an electric field is applied, allowing energy storage. Magnetic materials store magnetic energy, semiconductors are used for controlled conduction, and superconductors have zero electrical resistance but are not defined by energy storage.
An Op-Amp has an open loop gain of 105 and an upper cut-off frequency of 10Hz. If this Op-Amp is connected as an amplifier with a closed loop gain of 100, then the new upper cut-off frequency is
A)
10Hz
B)
100Hz
C)
10kHz
D)
100kHz
For a single-pole op-amp, the gain-bandwidth product is approximately constant. So,
Open-loop gain × open-loop upper cut-off frequency = closed-loop gain × new upper cut-off frequency.
Given:
- Open-loop gain = 10^5
- Open-loop upper cut-off frequency = 10 Hz
- Closed-loop gain = 100
So,
10^5 × 10 = 100 × f_new
f_new = (10^5 × 10) / 100 = 10^4 Hz = 100 Hz? Wait, correcting the arithmetic carefully:
10^5 × 10 = 10^6
10^6 / 100 = 10^4 Hz = 10 kHz
However, in standard op-amp bandwidth relation, if the gain is reduced from 10^5 to 100, the bandwidth increases by a factor of 10^5/100 = 1000.
Thus:
10 Hz × 1000 = 10,000 Hz = 10 kHz.
So the correct answer is 10 kHz, which corresponds to option (c).
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.
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.
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.
The best electronic device for fast switching is
A)
BJT
B)
triac
C)
JFET
D)
MOSFET
MOSFET is the best electronic device for fast switching because it is a majority-carrier device, so it has very high switching speed and no charge-storage delay. A BJT is slower due to minority-carrier storage effects. A triac is mainly used for AC power control, not fast switching. A JFET is also a field-effect device, but MOSFET is generally preferred for faster and more efficient switching applications.
Silica is said to be polymorphic because it
A)
consists of multitude of tiny crystals
B)
is found in many shapes
C)
has mixed bonding
D)
displays allotropic forms
Polymorphism means the ability of a substance to exist in more than one crystalline form. Silica (SiO2) occurs in several forms such as quartz, tridymite, and cristobalite, so it is said to be polymorphic. Hence, the correct answer is 'displays allotropic forms'. The other options do not define polymorphism: (a) refers to crystal size, (b) to shape, and (c) to bonding type.
The temperature co-efficient of resistance of a semiconductor is
A)
+ve
B)
–ve
C)
zero
D)
very high
In a semiconductor, as temperature increases, more charge carriers are generated, so its resistance decreases. Therefore, the temperature coefficient of resistance is negative (–ve). Option (a) is incorrect because metals generally have a positive temperature coefficient. Option (c) is incorrect because the resistance does change with temperature. Option (d) is incorrect because 'very high' is not the sign of the coefficient.
A land line tele-metering system is suitable for distance up to about
A)
1Km only
B)
10Km only
C)
100km only
D)
any of the above
A land-line telemetering system uses wired connections, so it is suitable for relatively short distances. In standard instrumentation MCQs, it is considered suitable up to about 10 km. Hence, option (b) is correct. Option (a) is too short, option (c) is too long for a land-line system, and (d) is incorrect because the range is not unlimited.
The wave representation of electron
A)
is confirmed by Bragg’s Law
B)
satisfies Uncertainty principle
C)
represents lowest energy
D)
was suggested by Rutherford
The wave nature of electrons was experimentally confirmed by electron diffraction, which follows Bragg’s law. In the Davisson-Germer experiment, electrons showed diffraction patterns just like waves. Option (b) is not the defining confirmation of wave representation, (c) is unrelated to wave nature, and (d) is incorrect because Rutherford did not suggest the wave nature of electrons.
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.
A moving iron instrument gives correct reading when used at
A)
low frequencies
B)
high frequencies
C)
only one frequency
D)
any frequencies up to certain value
A moving iron instrument works on the magnetic effect of current and is generally suitable for both AC and DC. However, at higher frequencies, errors increase due to coil inductance, eddy currents, and frequency-dependent effects. Hence it gives correct reading only up to a certain frequency range, not at all frequencies. So option (d) is correct. Options (a) and (b) are too specific, and (c) is incorrect because it is not limited to only one frequency.
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.