← MES Jr. Grade
Past Questions
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 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.
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.
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.
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.
Which of the following materials is not used as a fuse material?
A)
silver
B)
copper
C)
aluminium
D)
carbon
A fuse material should have low melting point, low resistivity, and stable characteristics. Silver, copper, and aluminium can be used in fuse elements in suitable forms/alloys. Carbon is not used as a fuse material because it does not have the required low melting and fuse characteristics.
The number of atoms per unit cell in the F.C.C. structure is
A)
2
B)
4
C)
14
D)
16
In a face-centered cubic (F.C.C.) unit cell: 8 corner atoms contribute 8 × 1/8 = 1 atom, and 6 face-centered atoms contribute 6 × 1/2 = 3 atoms. Total = 1 + 3 = 4 atoms per unit cell. Hence, the correct answer is 4. Option (a) 2 is for B.C.C., while (c) 14 and (d) 16 are incorrect.
An element can form a strongly magnetic solid only if its atoms have
A)
an incomplete valence shell
B)
an incomplete inner shell
C)
a vacant inner shell
D)
none of the above
Strong magnetism in solids is generally due to unpaired electrons in the inner d or f shells. These incomplete inner shells allow atomic magnetic moments to align strongly, producing ferromagnetic or strongly magnetic behavior. An incomplete valence shell alone is not the key requirement, and a vacant inner shell would not produce magnetism.
Resistivity of a wire depends on
A)
length
B)
material
C)
cross sectional area
D)
none of these
Resistivity is an intrinsic property of a substance, so it depends on the material of the wire. It does not depend on the wire’s length or cross-sectional area. Length and area affect resistance, not resistivity. Hence, the correct option is (b) material.
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 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.
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 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.
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).
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.
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.
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.
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.
A 0 – 200V voltmeter has a sensitivity of 1KΩ/V. The resistance of the voltmeter is
A)
100KΩ
B)
200KΩ
C)
1KΩ
D)
50KΩ
Sensitivity of a voltmeter = resistance per volt = 1 kΩ/V. For a 0–200 V voltmeter, total resistance = 1 kΩ/V × 200 V = 200 kΩ. Hence the correct option is (b).
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.
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.