← MES Jr. Grade
Past Questions
if the diameter of a wire is doubled, its current carrying capacity becomes
A)
One fourth
B)
Half
C)
Twice
D)
Four times
Current carrying capacity of a wire is proportional to its cross-sectional area. Since area is proportional to the square of diameter, doubling the diameter makes the area 2^2 = 4 times. Therefore, the current carrying capacity becomes four times. Option (a), (b), and (c) are incorrect because they do not account for the square relation between diameter and area.
Ferromagnetic materials are those which
A)
cannot be polarised
B)
have a permanent polarisation
C)
have u, equal to zero
D)
have u, equal to zero
Ferromagnetic materials are materials that can retain magnetization even after the external magnetic field is removed, so they exhibit permanent magnetization/polarisation. Hence option (b) is correct. Option (a) is wrong because ferromagnetic materials can be strongly magnetized. Options (c) and (d) are incorrect because ferromagnetic materials do not have zero permeability; in fact, they have very high relative permeability.
The power dissipation in a transistor is the product of
A)
emitter current and emitter to base voltage
B)
emitter current and collector to emitter voltage
C)
collector current and collector to emitter voltage
D)
none of these
The power dissipated in a transistor is given by the product of the current through it and the voltage across it. For a BJT, the main power dissipation is approximately VCE × IC, i.e., collector current multiplied by collector-to-emitter voltage. Hence, option (c) is correct. Option (a) is not the usual transistor power dissipation formula, option (b) is not standard, and option (d) is incorrect because (c) is valid.
The law J=o E, where J is current density, o is electrical conductivity and E is electric field strength is
A)
Ohm’s law
B)
Gauss’s law
C)
Bio-Savart’s law
D)
Ampere’s law
The relation J = σE (written here as J = oE) states that current density is directly proportional to electric field strength, with conductivity as the proportionality constant. This is the microscopic form of Ohm’s law. Gauss’s law relates electric flux to charge, Biot-Savart’s law gives magnetic field due to current, and Ampere’s law relates magnetic field circulation to current.
Norton’s equivalent circuit
A)
Is same as Thevenin’s circuit
B)
Has no relation with Thevenin’s circuit
C)
Is dual of Thevenin’s circuit
D)
Is reciprocal of Thevenin’s circuit
Norton’s equivalent circuit consists of a current source in parallel with a resistance, while Thevenin’s equivalent circuit consists of a voltage source in series with a resistance. These two forms are duals of each other. Hence, Norton’s circuit is the dual of Thevenin’s circuit. Option (a) is incorrect because they are not the same form, (b) is incorrect because they are directly related, and (d) is incorrect because reciprocity is a different network property.
The nature of crystal binding in Germanium is .
A)
ionic
B)
metallic
C)
covalent
D)
Van-der-wall type
Germanium is a group IV semiconductor. Each Ge atom has four valence electrons and forms four covalent bonds with neighboring atoms in the crystal lattice. Therefore, the crystal binding in germanium is covalent. Ionic bonding involves electron transfer, metallic bonding involves a sea of free electrons, and Van der Waals bonding is weak intermolecular attraction, none of which describe germanium’s crystal structure.
Which of the following is a passive component?
A)
Semi-conductor device
B)
Vacuum tube device
C)
Capacitors
D)
All of these
A passive component does not generate power; it only stores, dissipates, or releases energy. A capacitor is a passive component because it stores electrical energy in an electric field. Semiconductor devices and vacuum tube devices are active components because they can control current and provide amplification.
Two coupled coils with self inductances of 4mH and 16 mH are connected in series. The maximum possible value of inductances can be
A)
36mH
B)
20 mH
C)
28mH
D)
64mH
For two coupled coils connected in series, the equivalent inductance is maximum when the coupling is aiding: L = L1 + L2 + 2M. The maximum mutual inductance is M = sqrt(L1L2) = sqrt(4 × 16) = 8 mH. So, Lmax = 4 + 16 + 2(8) = 36 mH. However, since the question asks for the maximum possible value of inductances and the options include 36 mH, the correct answer is 36 mH. The option 28 mH corresponds to the case of series opposing connection: L = 4 + 16 - 2(8) = 4 mH? Actually, 28 mH is not the maximum. Therefore the correct option is (a) 36 mH.
z-transform converts convolution of time-signals to
A)
addition
B)
subtraction
C)
multiplication
D)
division
The z-transform turns convolution in the time domain into multiplication in the z-domain. If x[n] * h[n] is the convolution of two discrete-time signals, then Z{x[n] * h[n]} = X(z)H(z). Hence the correct option is multiplication. Addition, subtraction, and division are not the convolution property of the z-transform.
The color code of 1K Q, resistance is
A)
black, brown, red
B)
red, brown, brown
C)
brown, black, red
D)
black, black, red
For a 3-band resistor code, the first two bands give the significant digits and the third band is the multiplier.
1 kΩ = 1000 Ω = 10 × 10^2.
So the digits are 1 and 0, which are brown and black, and the multiplier 10^2 is red.
Therefore the correct color code is brown, black, red.
Option (a) gives 01 × 10^2 = 100 Ω, (b) gives 11 × 10^1 = 110 Ω, and (d) gives 00 × 10^2 = 0 Ω.
In an intrinsic semiconductor, the number of electrons is equal to the number of holes at which temperature?
A)
0°K
B)
0°c
C)
high temperature
D)
at all temperature
In an intrinsic semiconductor, electron-hole pairs are generated thermally in equal numbers. Therefore, the number of electrons is always equal to the number of holes at any temperature, including room temperature and other temperatures. Option (a) is wrong because at 0 K an intrinsic semiconductor has no free carriers. Options (b) and (c) are not correct because the equality is not limited to only 0°C or high temperature.
In what state is a silicon diode if the voltage drop across it is about 0.7V?
A)
No bias
B)
Forward bias
C)
Reverse bias
D)
Zener region
A silicon diode typically has a forward voltage drop of about 0.7 V when it is conducting. This means the diode is in forward bias. In no bias, there is no applied voltage; in reverse bias, the diode blocks current and does not show the normal 0.7 V drop; and the Zener region refers to reverse breakdown operation, not the usual silicon diode forward drop.
An ideal current source has
A)
Infinite source resistance
B)
Zero source resistance
C)
Large value of source resistance
D)
Finite value of source resistance
An ideal current source must deliver a constant current independent of the load. To do this, its internal/source resistance must be infinite, so that no current is diverted internally. A zero or finite resistance would allow the source current to vary with load, which is not ideal.
In a transistor-switching network, the operating point switches from ___ to ___ regions along the load line.
A)
cutoff, active
B)
cutoff, saturation
C)
active, saturation
D)
none of these
In a transistor switching circuit, the transistor is used as a switch, so it operates between two extreme regions: cutoff (OFF) and saturation (ON). Along the load line, the operating point moves from cutoff to saturation during switching. The active region is mainly used for amplification, not switching. Therefore, the correct answer is cutoff to saturation.
Assuming the Fermi level E_f to be independent of temperature, E_f may be defined as the level with an occupancy probability of
A)
0%
B)
50%
C)
75%
D)
100%
By definition, the Fermi level is the energy level at which the probability of occupancy by an electron is 1/2, i.e., 50%, when considering the Fermi-Dirac distribution. So the correct option is (b). The other options are incorrect because occupancy at the Fermi level is neither 0%, 75%, nor 100%.
The r.m.s. value of half wave rectified current is 50A. Its r.m.s. value for full wave rectification would be
A)
100A
B)
(50/sqrt(2))A
C)
(100/sqrt(2))A
D)
70.7A
For a sinusoidal current, the RMS value after half-wave rectification is I_m/2, while after full-wave rectification it is I_m/\sqrt{2}. Given half-wave RMS = 50 A, we get I_m = 100 A. Therefore full-wave RMS = 100/\sqrt{2} = 70.7 A. Hence, option (d) is correct. The other options do not match the standard RMS relations for rectified sine waves.
Which of the following are donor impurities? 1. Gold; 2. Phosphorus; 3. Boron; 4. Antimony; 5. Arsenic; 6. Indium
A)
2,4,5
B)
3,4, 5,6
C)
1,2, 4,6
D)
1,2,3
Donor impurities are pentavalent (Group V) atoms that donate extra electrons to a semiconductor. Phosphorus (2), Antimony (4), and Arsenic (5) are donor impurities. Boron and Indium are trivalent acceptor impurities, while Gold is not a donor impurity in this context. Hence the correct set is 2, 4, 5.
Under low level injection assumption, the injected minority carrier current for an extrinsic semiconductor is essentially the
A)
diffusion current
B)
drift current
C)
recombination current
D)
induced current
Under low-level injection in an extrinsic semiconductor, the injected minority carriers create a concentration gradient. Carrier motion due to this gradient is diffusion, so the injected minority carrier current is essentially diffusion current. Drift current is mainly due to an electric field, recombination current is not the transport mechanism here, and induced current is not relevant in this context.
The transition temperature of superconducting material is changed by which one of the following?
A)
Electric Field
B)
Magnetic Field
C)
Mechanical Stress
D)
None of these
The transition temperature (critical temperature) of a superconducting material is affected by an external magnetic field. A magnetic field can suppress superconductivity and lower the temperature at which the material becomes superconducting. Electric field is not the usual factor for changing the superconducting transition temperature in this context, and while mechanical stress may affect some material properties, the standard answer here is magnetic field.
When two honest coins are simultaneously tossed, the probability of two heads on any given trial is
A)
1
B)
3/4
C)
1/2
D)
1/4
When two honest coins are tossed, the equally likely outcomes are HH, HT, TH, and TT. Only one outcome, HH, gives two heads. So the probability = 1/4. The other options are incorrect because 1 is certain, 3/4 is too high, and 1/2 corresponds to one head in a single coin toss.
In which region are both the collector-base and base-emitter junctions forward-biased?
A)
Active
B)
Cutoff
C)
Saturation
D)
All of these
In a BJT, the saturation region occurs when both the base-emitter junction and the collector-base junction are forward-biased. In the active region, the base-emitter junction is forward-biased but the collector-base junction is reverse-biased. In cutoff, both junctions are reverse-biased. Therefore, the correct answer is Saturation.
When a potential is applied across an intrinsic semiconductor, holes flow
A)
towards positive terminal
B)
away from positive terminal
C)
in the external circuit only
D)
None of these
In an intrinsic semiconductor, holes are positive charge carriers. When a potential difference is applied, holes drift toward the negative terminal, which is equivalent to saying they move toward the positive terminal of the electric field direction? Wait—by conventional current direction, positive carriers move toward the negative terminal. However, in standard semiconductor MCQs, the intended statement is that holes flow in the direction of the electric field, i.e., toward the negative terminal. Since that option is not given, the closest correct exam answer is usually option (a) only if the question is asking about current direction. But strictly, the physics is that holes move toward the negative terminal, so the options appear inconsistent.
If a sample of germanium and a sample of silicon have the same impurity density and are kept at room temperature
A)
both will have equal value of resistivity
B)
both will have equal negative resistivity
C)
resistivity of silicon will be higher than that of germanium
D)
resistivity of germanium will be higher than that of silicon
For the same impurity density at room temperature, silicon has a larger band gap than germanium, so it has fewer thermally generated charge carriers and hence higher resistivity. Germanium, with its smaller band gap, conducts better and therefore has lower resistivity. So the resistivity of germanium is higher than that of silicon is incorrect? Wait—let's compare carefully: because Ge is more conductive, its resistivity is lower. Therefore silicon's resistivity is higher than germanium's. The correct option is (c).
The Fourier transform (FT) of a function x (t) is X (f). The FT of dx(t)/dt will be
A)
dX(f) df
B)
2infX(f)
C)
j2πfX(f)
D)
X(f) Gf
Using the Fourier transform differentiation property, if x(t) ↔ X(f), then d x(t)/dt ↔ j2πf X(f). This is because differentiation in the time domain corresponds to multiplication by j2πf in the frequency domain. Hence option (c) is correct. The other options do not match the standard FT property.
Avalanche breakdown is primarily dependent on the phenomenon of
A)
collision
B)
doping
C)
ionisation
D)
recombination
Avalanche breakdown occurs when charge carriers accelerated by a strong electric field gain enough energy to knock out additional electrons from atoms. This creates more carriers in a chain reaction, which is called impact ionisation. Hence, avalanche breakdown is primarily dependent on ionisation. Collision is only the mechanism that leads to ionisation, while doping mainly affects breakdown voltage and recombination opposes carrier multiplication.