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Past Questions — 2026
Laplace’s equation (∇²V = 0) is valid when:
A)
Charge present in region
B)
Charge absent in region
C)
Current flowing in conductor
D)
Magnetic field present
Laplace’s equation is \(\nabla^2 V = 0\), which is obtained from Poisson’s equation \(\nabla^2 V = -\rho/\varepsilon_0\) when the charge density \(\rho = 0\). So it is valid in a charge-free region. If charge is present, Poisson’s equation applies instead. Current flow or magnetic field presence does not determine Laplace’s equation for electrostatic potential.
Which Maxwell equation represents Gauss’s law for electricity?
A)
∇ · D = ρ
B)
∇ × E = –∂B/∂t
C)
∇ · B = 0
D)
∇ × H = J
Gauss’s law for electricity states that the electric flux density D has divergence equal to the free charge density ρ. In differential form, this is ∇ · D = ρ. The other options are different Maxwell equations: (b) is Faraday’s law of induction, (c) is Gauss’s law for magnetism, and (d) is Ampère–Maxwell law.
A Multiplexer (MUX) is also known as:
A)
Data Distributor
B)
Data Selector
C)
Code Converter
D)
Signal Amplifier
A multiplexer (MUX) selects one of several input signals and forwards it to a single output line, so it is called a Data Selector. A Data Distributor is the function of a demultiplexer (DEMUX), while a Code Converter and Signal Amplifier are different digital/electronic devices.
Nichols chart is used to represent:
A)
Gain vs phase
B)
Time vs amplitude
C)
Frequency vs time
D)
Voltage vs current
A Nichols chart is a frequency-domain plot used in control systems to represent the open-loop gain and phase of a system on the same graph. Specifically, it plots gain in dB versus phase angle, so option (a) is correct. The other options describe unrelated relationships: time vs amplitude is a time-domain waveform, frequency vs time is not the standard purpose of Nichols chart, and voltage vs current is an electrical V-I characteristic.
Explain the principle of operation of push pull amplifier circuit using transistors.
Design a 4-bit BCD to Excess-3 code converter. Simplify the output expressions using K-maps and draw the corresponding gate-level circuit diagram.
Convert JK flip flop to T flip flop.
Implement the following function with a multiplexer: F (A, B, C, D) = Σ (0,1,3,4,8,9,15)
Explain the working of an operational amplifier (Op-Amp) and discuss any two basic applications of Op-Amp circuits.
The electric potential in a region is V = 3x^2 + 5y^2 + 2z^2. Calculate ∇²V. Determine the charge density ρ using Poisson’s equation.
Explain the concept of electrostatic field intensity and electric potential. Derive the relation between electric field and potential.
Determine the Laplace transform of f(t) = e^(-3t)sin(2t).
Design a 2-bit magnitude comparator.
Standing waves on transmission lines occur due to:
A)
Impedance matching
B)
Reflection of waves
C)
Amplification of signals
D)
Noise interference
Standing waves on transmission lines are formed when the incident wave traveling along the line is reflected back from a load mismatch. The forward and reflected waves interfere with each other, producing fixed points of maximum and minimum voltage/current. Hence, the cause is reflection of waves. Impedance matching reduces reflections, amplification is unrelated, and noise interference does not create standing waves.
The dual of (A+1) = 1 is:
A)
A . 1 = 1
B)
A + 0 = 0
C)
A . 0 = 0
D)
A + 1 = 0
To find the dual in Boolean algebra, interchange '+' with '·' and interchange 1 with 0. Starting from (A + 1) = 1, the dual becomes A · 0 = 0. This is option (c). Option (a) is not the dual because it still keeps '+' and 1 unchanged in the same places.
Which plot is commonly used for frequency response analysis?
A)
Root locus plot
B)
Bode plot
C)
Time response plot
D)
State plot
A Bode plot is commonly used for frequency response analysis because it shows the system's gain and phase versus frequency. Root locus is used for studying how closed-loop poles move with gain, time response plot shows output versus time, and state plot is not a standard frequency-response tool.
Poisson’s equation relates electric potential with:
A)
Current density
B)
Magnetic flux
C)
Charge density
D)
Electric conductivity
Poisson’s equation in electrostatics is ∇²V = -ρ/ε, where V is electric potential, ρ is charge density, and ε is permittivity. Thus, electric potential is directly related to charge density. Current density, magnetic flux, and electric conductivity are not the quantities connected by Poisson’s equation.
Reduce the expression f = Σm (0,2,3,4,5,6) using mapping and implement it in NAND logic gates.
A feature that distinguishes a JK flip flop from an SR flip flop is:
A)
Toggle conditions
B)
Preset input
C)
Types of clock
D)
Clear input
A JK flip-flop is an improved version of the SR flip-flop. In an SR flip-flop, the S = R = 1 condition is invalid/indeterminate. The JK flip-flop removes this ambiguity by allowing the same input combination (J = K = 1) to produce a toggle operation. That toggle feature is what distinguishes it from the SR flip-flop. Preset and clear inputs are not the distinguishing feature here, and clock type is not the key difference.
Waveguides are mainly used for transmission of:
A)
Low frequency signals
B)
Audio signals
C)
Microwave signals
D)
DC signals
Waveguides are hollow conducting structures designed to carry electromagnetic waves efficiently at very high frequencies, especially in the microwave range. They are not suitable for low-frequency, audio, or DC transmission because those signals do not propagate effectively in waveguide structures. Hence, the correct answer is microwave signals.
The Nyquist criterion is mainly used for:
A)
Time response analysis
B)
Stability analysis of feedback systems
C)
Signal filtering
D)
State-space modeling
The Nyquist criterion is used to determine the stability of feedback control systems by analyzing the open-loop frequency response and its encirclements of the critical point −1 + j0. It is not meant for time response analysis, signal filtering, or state-space modeling. Those topics are handled by different methods such as transient analysis, filter design techniques, and state-space methods respectively.
A compensator used to improve transient response is:
A)
Lead compensator
B)
Lag compensator
C)
Integral compensator
D)
PI controller
A lead compensator is used to improve transient response because it adds positive phase lead, increasing phase margin, speeding up the system response, and reducing overshoot and settling time. Lag compensators mainly improve steady-state accuracy, not transient response. Integral compensators and PI controllers are primarily used to reduce steady-state error, though PI may affect transient behavior, it is not the standard answer here.
If two stages of a cascaded amplifier have gains of 60 dB and 30 dB, the overall gain is:
A)
90 dB
B)
180 dB
C)
2 dB
D)
1800 dB
For cascaded amplifiers, gains in decibels add directly. So the overall gain = 60 dB + 30 dB = 90 dB. The other options are incorrect because 180 dB and 1800 dB are far too large, and 2 dB is not the sum of the given gains.
A Wien Bridge Oscillator is commonly used to generate:
A)
Square waves
B)
Triangular waves
C)
Sinusoidal waves
D)
Pulse waves
A Wien Bridge Oscillator is a standard RC oscillator designed to produce low-distortion sinusoidal output. It uses a frequency-selective bridge network that provides the required positive feedback at one specific frequency. The other options are incorrect because square, triangular, and pulse waves are typically generated by multivibrators, relaxation oscillators, or waveform-shaping circuits, not a Wien Bridge Oscillator.
The 2’s complement of 1000_2 is:
A)
0111
B)
0101
C)
1000
D)
0001
For 2’s complement, first take the 1’s complement of the binary number and then add 1.
Given: 1000₂
1’s complement = 0111₂
Add 1: 0111 + 1 = 1000₂
However, since the question asks for the 2’s complement of 1000₂ in the usual fixed 4-bit form, the result is the same pattern as the original number, i.e., 1000₂. But among the provided options, the intended answer is usually obtained by taking only the 1’s complement and adding 1 to the least significant bit in a different interpretation, which is not correct here.
So the mathematically correct 2’s complement of 1000₂ is 1000₂, which corresponds to option (c).