← MES Jr. Grade
Past Questions — 2012
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.
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.
Two bulbs marked 200 watt - 250 Volts and 100 watt - 250 Volts are connected in series to 250 Volts supply. Power consumed in circuit is
A)
33 watt
B)
66.667watt
C)
100 watt
D)
300 watt
For each bulb, use its rated resistance: R = V^2 / P.
For 200 W, 250 V bulb: R1 = 250^2 / 200 = 312.5 ohm.
For 100 W, 250 V bulb: R2 = 250^2 / 100 = 625 ohm.
Since they are in series, total resistance:
R = 312.5 + 625 = 937.5 ohm.
Current from 250 V supply:
I = V / R = 250 / 937.5 = 0.2667 A.
Total power consumed:
P = V × I = 250 × 0.2667 ≈ 66.67 W.
So the correct option is (b) 66.667 watt.
Note: Option (a) 33 watt is incorrect; the correct computed power is about 66.7 W.
In a JFET, point of reference is
A)
drain
B)
source
C)
gate
D)
none of these
In a JFET, the source terminal is taken as the point of reference because the gate-to-source voltage (V_GS) controls the channel conductivity. The source is commonly used as the reference terminal for measuring the input/control voltage. Drain is the output terminal, and gate is the controlling terminal, so they are not the usual reference point.
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.
Which is the displacement transducer with excellent sensitivity, linearity and resolution?
A)
incremental encoder
B)
absolute encoder
C)
LVDT
D)
strain gauge
An LVDT (Linear Variable Differential Transformer) is a displacement transducer known for excellent sensitivity, good linearity, and very high resolution. It converts linear displacement into a proportional electrical signal with minimal friction and wear. An incremental encoder measures relative position in pulses, an absolute encoder gives position in coded form, and a strain gauge is mainly used for strain measurement, not displacement.
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 materials does not have covalent bonds?
A)
metals
B)
diamond
C)
organic polymers
D)
silicon
Metals are held together mainly by metallic bonding, not covalent bonding. Diamond is a giant covalent crystal, organic polymers contain covalent bonds in their chains, and silicon also forms a covalent network structure. Therefore, the material that does not have covalent bonds is 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.
Resistance of a wire is r ohms. The wire is stretched to double its length then its resistance in ohms is
A)
r/2
B)
4r
C)
2r
D)
r/4
For a wire, resistance R = ρL/A. When the wire is stretched to double its length, its volume remains constant, so the cross-sectional area becomes half. Thus new resistance R' = ρ(2L)/(A/2) = 4ρL/A = 4r. Therefore, the resistance becomes 4r.
Which of these has a magnetic brake?
A)
thermo couple ammeter
B)
energy meter
C)
dynamometer ammeter
D)
frequency meter
A magnetic brake is used in an induction-type energy meter to provide controlling/braking torque. The aluminium disc in the meter cuts the magnetic field of a permanent magnet, producing eddy currents that create the braking effect. A thermocouple ammeter, dynamometer ammeter, and frequency meter do not use a magnetic brake in this way.
JFET can operate in
A)
depletion mode and enhancement mode
B)
depletion mode only
C)
enhancement mode only
D)
neither enhancement nor depletion mode
A JFET (Junction Field Effect Transistor) is a normally ON device. Its channel conducts at zero gate bias, and applying reverse gate voltage only depletes the channel and reduces current. It does not operate in enhancement mode. Therefore, the correct answer is depletion mode only.
The main advantage of a successive approximation ADC is that
A)
it is independent of its chopper frequency
B)
it has high series mode rejection
C)
it can operate faster than other ADCs
D)
its conversion time can be varied
A successive approximation ADC performs conversion by binary search, so it needs only a fixed number of steps equal to the number of bits. This makes it much faster than integrating-type ADCs and suitable for general-purpose data acquisition. Option (a) is unrelated to SAR ADCs, option (b) refers to common-mode rejection in instrumentation amplifiers, and option (d) is not the main advantage because SAR ADC conversion time is generally fixed for a given resolution.
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.
Which statement about MOSFET is false? MOSFETs can operate in
A)
depletion mode
B)
enhancement mode
C)
both depletion & enhancement mode
D)
depletion only mode
MOSFETs can operate in both depletion mode and enhancement mode. Therefore, the statement "MOSFETs can operate in depletion only mode" is false. Options (a), (b), and (c) are all true descriptions of MOSFET operation.
The household analog energy meter is
A)
indicating instrument
B)
recording instrument
C)
integrating instrument
D)
none of these
A household analog energy meter measures the total electrical energy consumed over time, usually in kWh. Instruments that measure the total quantity over a period are called integrating instruments. An indicating instrument shows the instantaneous value, and a recording instrument records variations over time, so they are not correct here.
Dielectric strength of impregnated paper is
A)
40-50 KV/cm
B)
200- 300 KV/cm
C)
500-600 KV/cm
D)
800-900 KV/cm
Impregnated paper has a dielectric strength in the range of about 200 to 300 kV/cm. This is much higher than plain paper because impregnation removes air gaps and improves insulation. The other options are either too low or unrealistically high for impregnated paper.
Eutectoid transformation in an alloy is a reaction of which type?
A)
Solid ↔ liquid
B)
liquid ↔ liquid
C)
solid ↔solid
D)
any of these
A eutectoid transformation is a solid-state phase transformation in which one solid phase changes into two different solid phases on cooling, or the reverse on heating. Therefore, it is a solid ↔ solid reaction. Option (a) is a solid–liquid reaction, and option (b) is not a eutectoid transformation. Hence, the correct answer is (c).
When bias is applied to a varicap diode is increased, its capacitance
A)
decreases
B)
increases
C)
remains constant
D)
increases than decreases
A varicap (varactor) diode works as a voltage-controlled capacitor. When the reverse bias is increased, the depletion layer widens, so the junction capacitance decreases. Hence, the correct answer is (a) decreases.
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.
The voltage comparator can be used in A/D conversion as a
A)
1-bit quantizer
B)
2-bit quantizer
C)
4-bit quantizer
D)
8-bit quantizer
A voltage comparator in A/D conversion compares the input voltage with a reference level and gives only one of two outputs: high or low. This is equivalent to a 1-bit quantizer, because it can represent only two levels. A 2-bit, 4-bit, or 8-bit quantizer would require 4, 16, or 256 discrete levels respectively, which a single comparator cannot provide.
The miller indices are the same for
A)
perpendicular planes
B)
crystal planes
C)
parallel planes
D)
3 crystallographic axes
Miller indices represent a family of crystal planes that are parallel to each other and equally spaced. Any two parallel planes in the same family have the same Miller indices. Perpendicular planes generally have different indices, and crystallographic axes are described by direction indices, not Miller indices.
The element of electric heater is made of
A)
copper
B)
steel
C)
carbon
D)
nichrome
The heating element of an electric heater is made of nichrome because it has high electrical resistance, a high melting point, and does not oxidize easily at high temperatures. Copper is a very good conductor and would not produce enough heat, steel is not suitable as a heating element, and carbon is not commonly used for electric heater elements in this context.
When P=power, V= voltage, I= current, R=resistance and G= conductance. Which of the following relation is incorrect?
A)
V = √ (PR)
B)
P = V2G
C)
G = P/I2
D)
I = √(P/R)
Use the basic power relations: P = VI = I^2R = V^2/R. Also, conductance G = 1/R.
Check each option:
- (a) V = √(PR): From P = V^2/R, we get V^2 = PR, so V = √(PR). Correct.
- (b) P = V^2G: Since G = 1/R, P = V^2/R = V^2G. Correct.
- (c) G = P/I^2: From P = I^2R, we get R = P/I^2, so G = 1/R = I^2/P, not P/I^2. Incorrect.
- (d) I = √(P/R): From P = I^2R, we get I^2 = P/R, so I = √(P/R). Correct.
Therefore, the incorrect relation is (c).
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.