← MES Jr. Grade
Past Questions — 2012
Metals have thermal conductivities in the range of
A)
< 1
B)
1-5
C)
5-25
D)
20-400
Metals are good conductors of heat, so their thermal conductivity is generally high. In standard material science classifications, metals typically fall in the range of about 20 to 400 W/m·K. Options (a), (b), and (c) are too low and correspond more to poor conductors such as insulators or non-metals.
For carbon resistors what is the color for 5?
A)
green
B)
black
C)
orange
D)
gray
In the standard resistor color code, the digit 5 is represented by green. The sequence is: 0 black, 1 brown, 2 red, 3 orange, 4 yellow, 5 green, 6 blue, 7 violet, 8 gray, 9 white. Therefore, the correct option is green. Black is 0, orange is 3, and gray is 8.
A transducer must have
A)
good dynamic response
B)
good sensitivity
C)
good resolution
D)
all of above
A transducer should ideally have good dynamic response, good sensitivity, and good resolution. Good dynamic response ensures it can follow rapid changes in the measurand, good sensitivity allows it to detect small changes, and good resolution enables it to distinguish very small input variations. Therefore, the correct choice is 'all of above'.
If f(t) = -f(- t) and f(t) satisfies Drichlet conditions then f(t) can be expanded in Fourier series having
A)
sine terms alone
B)
cosine terms alone
C)
cosine and constant terms
D)
sine and constant terms
If f(t) = -f(-t), then f(t) is an odd function. For an odd function satisfying Dirichlet conditions, the Fourier series contains only sine terms because cosine terms and the constant term are even functions and their coefficients become zero over symmetric limits. Hence the expansion is in sine terms alone.
The Y plates of a CRO are excited by a voltage 2sin(100t) and X plates are not connected. The display would be
A)
a vertical line
B)
a horizontal line
C)
a sine wave
D)
a slanting line
In a CRO, the Y-plates control vertical deflection and the X-plates control horizontal deflection. Here, the Y-plates are given an AC voltage 2sin(100t), so the spot moves up and down vertically. Since the X-plates are not connected, there is no horizontal deflection, so the beam stays at a fixed X-position. Therefore, the display is a vertical line. A horizontal line would require only X-deflection, and a sine wave or slanting line would need both X and Y inputs.
Which of the following processes are used to harden steel?
A)
normalizing
B)
carburizing
C)
annealing
D)
all of these
Carburizing is a surface hardening process used to increase the carbon content at the surface of steel, followed by quenching to obtain a hard outer layer. Normalizing and annealing are heat-treatment processes mainly used to refine grain structure, relieve stresses, and soften steel, not to harden it. Therefore, the correct answer is carburizing.
Polyethylene is produced by
A)
condensation polymerization
B)
addition polymerization
C)
co-polymerization
D)
all of the above
Polyethylene is formed by polymerizing ethylene (CH2=CH2) through addition polymerization, where the double bond opens and monomers join without loss of any small molecule. Condensation polymerization involves elimination of small molecules like water or HCl, which does not occur here. It is not a copolymer because it is made from only one monomer type.
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.
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.
The junction capacitance of a varactor diode is 5pf with a reverse voltage of 4V. If this bias is increased to 16V then the capacitance would become
A)
20pf
B)
10pf
C)
2.5pf
D)
1.25pf
For a varactor diode, junction capacitance varies inversely with the square root of the reverse bias voltage: C ∝ 1/√V. Here, the voltage increases from 4 V to 16 V, i.e., by a factor of 4. So the capacitance becomes 5 pf / √4 = 5 pf / 2 = 2.5 pf. Hence, the correct option is (c).
Intrinsic semiconductor are those which
A)
are available locally
B)
are in the purest form
C)
have more electrons than holes
D)
have zero energy gap
An intrinsic semiconductor is a pure semiconductor with no intentional impurities (doping). In such materials, the number of electrons equals the number of holes. Option (a) is unrelated, (c) describes an extrinsic imbalance, and (d) is incorrect because intrinsic semiconductors do have a small but non-zero energy gap.
FETs have similar properties to
A)
PNP transistors
B)
NPN transistors
C)
thermionic valve
D)
UJTs
A field-effect transistor (FET) is a voltage-controlled device with very high input impedance, similar to a thermionic valve (vacuum tube) in its control principle. Like a valve, a small control voltage governs a larger current. By contrast, PNP/NPN transistors are current-controlled bipolar devices, and UJTs do not match the same characteristic behavior as closely.
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.
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.
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.
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.
A general purpose diode is more likely to suffer avalanche breakdown rather than zener breakdown because
A)
its leakage current is small
B)
it has strong co-valent bond
C)
it is lightly doped
D)
it has low reverse resistance
Avalanche breakdown occurs in a p-n junction when the depletion region is wide and the electric field accelerates carriers enough to cause impact ionization. A general-purpose diode is usually lightly doped, so it has a wider depletion layer and therefore is more likely to undergo avalanche breakdown. Zener breakdown, in contrast, is associated with heavily doped junctions and a very thin depletion region. Hence, the correct option is (c).
The potential energy of an orbiting electron in any atom is
A)
always +ve
B)
always –ve
C)
sometimes +ve
D)
less than its Kinetic energy
For an electron bound to an atom, the electrostatic potential energy is negative when the zero of potential energy is taken at infinite separation. Since the electron is attracted to the positively charged nucleus, it is in a bound state, so its potential energy remains negative. Hence, the correct option is (b). Options (a) and (c) are incorrect because the potential energy of a bound electron is not positive. Option (d) is not generally true as stated; the relation between potential and kinetic energy depends on the atomic model, but the sign of potential energy is always negative for a bound electron.
The instrument used to check insulation of household wiring is
A)
megger
B)
ohm-meter
C)
multimeter
D)
All of above
A megger (megohmmeter) is specifically used to measure very high resistance, such as the insulation resistance of household wiring. An ohm-meter or multimeter can measure resistance, but they are not suitable for proper insulation testing because insulation resistance is usually in the megaohm range. Therefore, the correct answer is megger.
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.
IEEE488 standard is based on the transmission of
A)
4 bit
B)
8 bit
C)
16 bit
D)
24 Bit
IEEE-488 (also called GPIB) is a parallel digital interface standard that uses an 8-bit data bus for transmission. Hence, it is based on the transmission of 8 bits. The other options do not match the standard data width used in IEEE-488.
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.