← MES Jr. Grade
Past Questions
For a distortionless line, the parameters are related as
A)
R/G=L/C
B)
=1
C)
R/G=C/L
D)
RG=LC
For a distortionless transmission line, the Heaviside condition must be satisfied: R/L = G/C. Rearranging gives R/G = L/C. This ensures that attenuation is frequency-independent and the signal shape is not distorted. The other options do not represent the distortionless-line condition.
Polarisation of a wave is
A)
Direction of electric field
B)
Direction of magnetic field at some point in space
C)
Either (a) or (b)
D)
None of these
Polarisation of an electromagnetic wave is defined by the orientation of its electric field vector. For a plane EM wave, the magnetic field is always perpendicular to the electric field and the direction of propagation, so polarization is described using the electric field direction. Hence, option (a) is correct. Option (b) is incorrect because magnetic field direction is not used to define polarization, and option (c) is incorrect because only the electric field direction is the standard definition.
Ripple factor of an ideal rectifier is
A)
zero
B)
unity
C)
infinity
D)
none of these
Ripple factor is the ratio of the RMS value of the AC component to the DC component in the rectifier output. In an ideal rectifier, the output is pure DC with no AC ripple, so the ripple factor is 0. Hence, the correct answer is zero. Unity and infinity are incorrect because they imply significant ripple or no DC component, which is not the case for an ideal rectifier.
The driving-point impedance of a network is given by Z(s) = (s^2 + 2s + 6)/ s(s + 3). Then the number of energy storage elements present in the network is
A)
1
B)
2
C)
3
D)
4
For a driving-point impedance, the number of energy storage elements is indicated by the order of the network function after removing any common factors and identifying the poles/zeros that require reactive elements. Here, Z(s) = (s^2 + 2s + 6) / [s(s + 3)] has two poles: at s = 0 and s = -3. The numerator is a second-order polynomial, so the network is of second order and requires two energy storage elements. Hence, the correct answer is 2.
The process of conversion of continuous time signal into discrete time signal is known as
A)
aliasing
B)
sampling
C)
convolution
D)
none of these
The conversion of a continuous-time signal into a discrete-time signal is called sampling. In sampling, the signal is measured at discrete time instants. Aliasing is a distortion that can occur if sampling is done improperly, and convolution is a mathematical operation used in signal processing, not the conversion process.
For a two port network to be reciprocal, required condition is
A)
Z11=Z22
B)
Y12=Y21
C)
h11=h22
D)
AD-BC=0
For a reciprocal two-port network, the transfer parameters must be symmetric. In Y-parameters, the reciprocity condition is Y12 = Y21. Similarly, in Z-parameters it is Z12 = Z21, and in ABCD-parameters it is AD - BC = 1. Therefore, among the given options, Y12 = Y21 is the correct reciprocity condition. The other options are incorrect: Z11 = Z22 is not a reciprocity condition, h11 = h22 is not required for reciprocity, and AD - BC = 0 is wrong because for a reciprocal network the correct relation is AD - BC = 1.
In a JFET drain current is maximum when V_GS is
A)
zero
B)
negative
C)
positive
D)
V pinch off
In a JFET, the drain current is maximum at V_GS = 0 because the channel is fully open and the device conducts its maximum current, called I_DSS. For an n-channel JFET, making V_GS negative increases depletion region width, narrows the channel, and reduces drain current. A positive V_GS is generally not used for normal JFET operation, and pinch-off is the condition where current saturates, not where it is maximum.
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.
Which of the following is a periodic signal?
A)
Au(t)
B)
A sin(wt)
C)
Act
D)
At
A periodic signal repeats itself after a fixed interval T. The sinusoidal signal A sin(ωt) is periodic with period T = 2π/ω. The other options are not periodic: Au(t) is a step signal, Act is a ramp-like signal, and At is a straight-line signal; none of these repeat over time.
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.
The transfer function of a continuous time system is described by Y(s)/X(s) = (s^2 + 4s + 3) / (s^3 + 4s^2 + 1). The number of state variables in the state model of the system is
A)
1
B)
2
C)
3
D)
5
For a continuous-time LTI system, the number of state variables in a minimal state-space model equals the order of the transfer function denominator after any pole-zero cancellations. Here, the transfer function is (s^2 + 4s + 3) / (s^3 + 4s^2 + 1). The denominator is a cubic polynomial, so the system is third order. Therefore, it requires 3 state variables. The numerator degree does not determine the number of states, and there is no indication of cancellation that would reduce the order.
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.
Three resistances of 15Q; 10Q and 3Q are connected in parallel. The overall resistance is
A)
Less than 3Q
B)
Between 15 and 10Q
C)
Between 10 and 3Q
D)
More than 3Q
For resistors connected in parallel, the equivalent resistance is always less than the smallest individual resistance. Here the smallest resistance is 3Ω, so the overall resistance must be less than 3Ω. Therefore, option (a) is correct. Options (b), (c), and (d) are incorrect because parallel combination never gives a resistance greater than or equal to the smallest resistor.
The power in a series RLC circuit will be half of that at resonance when the magnitude of the current is equal to
A)
V2R
B)
V/sqrt(3)R
C)
V/sqrt(2)R
D)
sqrt(2)V/R
In a series RLC circuit, real power is P = I^2R. At resonance, impedance is purely resistive, so current is I_r = V/R and power is P_r = V^2/R. For the power to be half of resonance: P = P_r/2 = V^2/(2R). Using P = I^2R, we get I^2R = V^2/(2R), hence I = V/(sqrt(2)R). Therefore the correct option is (c).
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.
A signal m(t) is multiplied by a sinusoidal waveform of frequency f, such that v(t) = m(t) cos(2πft). If Fourier transform of m(t) is M(f), Fourier transform of v(t) will be
A)
0.5 M(f+f)
B)
0.5 M(f-f)
C)
0.5 M(f+f) + 0.5 M(f-f)
D)
0.5 M(f- f) + 0.5 M(f-f)
Using the modulation property of Fourier transform: multiplying a signal m(t) by cos(2πf0t) shifts its spectrum to both +f0 and -f0. Since cos(2πf0t) = (e^{j2πf0t} + e^{-j2πf0t})/2, the Fourier transform of v(t) = m(t)cos(2πf0t) becomes 0.5M(f-f0) + 0.5M(f+f0). Here the given frequency is f, so the correct form is 0.5M(f+f) + 0.5M(f-f). Options (a) and (b) show only one shifted copy, which is incomplete. Option (d) is incorrect because it repeats the same term and misses the +f shift.
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.
An open circuit can have any voltage across its terminals, but the current is always
A)
5A
B)
0A
C)
1A
D)
ow
In an open circuit, the path is broken, so no current can flow through it. The voltage across the open terminals may be any value, but the current is always zero. Hence, the correct answer is 0A. Option (a) 5A, (c) 1A, and (d) ow are incorrect because an open circuit does not allow current flow.
Which of the following is the poorest electrical conductor?
A)
steel
B)
carbon
C)
copper
D)
aluminium
Among the given materials, copper and aluminium are good electrical conductors, carbon conducts electricity better than steel in many forms (especially graphite), while steel has much higher electrical resistivity than the others. Therefore, steel is the poorest electrical conductor of the options.
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.
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.
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.
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.
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.
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.