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Past Questions — 2026
Classify signals and systems and analyze the properties of linear time-invariant (LTI) systems with suitable examples.
Discuss the properties of magnetic and ferroelectric materials and explain their relevance in modern electronic applications.
Which of the following is an even function?
A)
sin (x)
B)
cos (x)
C)
tan (x)
D)
x^3
An even function satisfies f(-x) = f(x). For cos(x), cos(-x) = cos(x), so it is even. In contrast, sin(x) and tan(x) are odd functions because sin(-x) = -sin(x) and tan(-x) = -tan(x). Also, x^3 is odd since (-x)^3 = -x^3.
The integration of a unit ramp function is:
A)
unit parabolic function
B)
unit ramp function
C)
unit step function
D)
unit impulse function
A unit ramp function is r(t) = t u(t). Integrating it gives ∫ r(t) dt = ∫ t u(t) dt = t^2/2 for t ≥ 0, which is called the unit parabolic function. A unit step function is the derivative of a ramp, and a unit impulse is the derivative of a step, so options (c) and (d) are incorrect. The ramp itself is not unchanged by integration, so (b) is also incorrect.
Correlation function measures:
A)
Voltage
B)
Power
C)
Similarity between signals
D)
Frequency
Correlation function is used to measure how closely two signals resemble each other as one is shifted relative to the other. In signals and systems, a higher correlation indicates greater similarity or alignment between signals. It does not measure voltage, power, or frequency directly.
Piezoelectric materials are used in:
A)
Heating
B)
Sensors and oscillators
C)
Cooling
D)
Storage
Piezoelectric materials generate an electric signal when mechanical stress is applied, and they also deform when an electric field is applied. Because of this property, they are widely used in sensors and oscillators (such as quartz crystal oscillators). The other options are incorrect because piezoelectric materials are not primarily used for heating, cooling, or storage.
Laplace transform of unit step function is:
A)
1
B)
s
C)
1/s
D)
s^2
The unit step function u(t) is 1 for t ≥ 0. Its Laplace transform is
L{u(t)} = ∫₀^∞ e^(-st) dt = [ -e^(-st)/s ]₀^∞ = 1/s, for s > 0.
So the correct option is (c) 1/s. The other options are not the standard Laplace transform of the unit step function.
Superposition theorem applies to:
A)
Non-linear circuits
B)
Linear circuits
C)
Mechanical systems
D)
Thermal systems
The superposition theorem is valid only for linear circuits, where the total response is the sum of the responses due to each independent source acting separately. It does not apply directly to non-linear circuits because their response is not proportional to excitation. Mechanical and thermal systems are not the standard context for this circuit theorem.
Zener diode regulation occurs in:
A)
Forward region
B)
Active region
C)
Breakdown region
D)
Saturation region
A Zener diode is designed to operate in reverse bias. When the reverse voltage reaches the Zener voltage, the diode enters the breakdown region, where it maintains nearly constant voltage. This is the region used for voltage regulation. The forward region is for normal conduction, the active region is a transistor term, and saturation region is also associated with transistors, not Zener diode regulation.
BJT is preferred for amplification because of:
A)
High input impedance
B)
High current gain
C)
Low voltage
D)
Low frequency
A BJT is commonly preferred in amplification because it provides a good current gain, meaning a small base current can control a much larger collector current. This makes it effective for amplifying signals.
Why others are incorrect:
- (a) High input impedance: This is a feature of FETs, not BJTs. BJTs have relatively low input impedance.
- (c) Low voltage: This is not a reason for preferring BJTs for amplification.
- (d) Low frequency: BJTs are used over a wide range of frequencies, but this is not the main reason for their use in amplification.
CMOS circuits are known for:
A)
High power
B)
High noise
C)
Low power consumption
D)
Low speed
CMOS (Complementary Metal-Oxide-Semiconductor) circuits are widely used because they consume very low static power, especially compared with other logic families. This makes them energy-efficient and suitable for battery-operated devices. The other options are incorrect because CMOS is not known for high power or high noise, and although some CMOS designs may trade off speed for power, the defining feature asked here is low power consumption.
Using nodal analysis, find I in the circuit diagram given below.
In a full wave bridge rectifier, the transformer’s secondary voltage is 100 sin vt. The forward resistance of each diode is 25Ω and load resistance is 950 Ω. Calculate D.C. output voltage, ripple factor, efficiency of rectification and PIV of the non-conducting diode.
For the circuit shown in the figure below, for R =300 kΩ, calculate IB, IC and VCE.
Ferroelectric materials are commonly used in:
A)
Motors
B)
Capacitors
C)
Generators
D)
Transformers
Ferroelectric materials have very high dielectric constants and spontaneous polarization that can be reversed by an electric field. Because of this, they are commonly used as dielectric materials in capacitors, especially for high-capacitance applications. Motors, generators, and transformers mainly rely on magnetic materials and electromagnetic induction, not ferroelectric behavior.
Explain the concept of drift current and diffusion current in semiconductors.
For energy signals, the energy will be finite and the average power will be:
A)
infinite
B)
finite
C)
zero
D)
cannot be defined
An energy signal is defined as a signal with finite total energy and zero average power. Since its energy is finite and concentrated over a limited duration, the long-term average power becomes 0. Therefore, the correct answer is (c) zero. Option (b) is incorrect because finite average power is a property of power signals, not energy signals.
Fourier series is applicable to:
A)
Random signals
B)
Periodic signals
C)
Noise
D)
Impulse
Fourier series represents a signal as a sum of sine and cosine terms, and it is specifically applicable to periodic signals. A periodic function can be decomposed into harmonically related sinusoidal components. Random signals and noise are generally analyzed using Fourier transform or statistical methods, while an impulse is not a periodic signal.
Hall coefficient is positive for:
A)
Metals
B)
n-type semiconductor
C)
p-type semiconductor
D)
Insulators
The Hall coefficient is positive when the dominant charge carriers are holes. In a p-type semiconductor, holes are the majority carriers, so the Hall voltage and Hall coefficient come out positive. In contrast, metals and n-type semiconductors generally have electrons as the dominant carriers, giving a negative Hall coefficient. Insulators do not conduct well enough for a meaningful Hall effect in the usual sense.
An SCR can be turned OFF by:
A)
interrupting its anode current
B)
reversing polarity of its anode-cathode voltage
C)
low current dropout
D)
All of the above
An SCR (Silicon Controlled Rectifier) can be turned OFF only by reducing its anode current below the holding current, which can be achieved by interrupting the anode current. It can also be turned off by applying reverse bias across the anode-cathode terminals, i.e., reversing the polarity of the anode-cathode voltage. The phrase 'low current dropout' here refers to the current falling below the holding/latching level, which also turns it OFF. Therefore, all the given methods point to turn-off conditions, so the correct answer is 'All of the above'.
The most important use of soft magnetic materials is in:
A)
meters
B)
transducers
C)
transformer and machine cores
D)
transformer winding wire
Soft magnetic materials are easy to magnetize and demagnetize, so they are used where the magnetic field must change repeatedly with low hysteresis loss. The most important application is in transformer and machine cores. Meters and transducers may use magnetic materials in some designs, but they are not the primary use. Transformer winding wire is made of conducting material like copper or aluminum, not magnetic material.
A full wave bridge rectifier is supplied voltage at 50 Hz. The lowest ripple frequency will be:
A)
400 Hz
B)
200 Hz
C)
100 Hz
D)
50 Hz
In a full-wave bridge rectifier, both half-cycles of the AC input are converted into output pulses. So the ripple frequency becomes twice the supply frequency. Given supply frequency = 50 Hz, ripple frequency = 2 × 50 = 100 Hz. Hence the lowest ripple frequency is 100 Hz. Option (a) 400 Hz is too high, (b) 200 Hz is too high, and (d) 50 Hz is the original supply frequency, not the full-wave ripple frequency.
Superconductors exhibit Meissner effect, meaning:
A)
High resistance
B)
Expulsion of magnetic field
C)
Heat generation
D)
Voltage drop
The Meissner effect is the complete expulsion of magnetic flux from the interior of a superconductor when it is cooled below its critical temperature. This is a defining property of superconductivity. Option (a) is wrong because superconductors have zero electrical resistance, not high resistance. Option (c) is wrong because superconductors do not primarily indicate heat generation. Option (d) is wrong because voltage drop is not the meaning of Meissner effect.
Explain the operation of a Bipolar Junction Transistor (BJT) in common emitter configuration and discuss its input and output characteristics.
Analyze the working of a Zener diode and explain its application in voltage regulation with a suitable circuit.