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Past Questions — 2026
Derive the expression for the electric field intensity due to an infinite line charge using Coulomb’s law.
Explain time-varying electromagnetic fields and displacement current.
In a balanced three-phase system, the sum of instantaneous phase currents is:
A)
Maximum
B)
Minimum
C)
Zero
D)
Infinite
In a balanced three-phase system, the three phase currents are equal in magnitude and 120° apart in phase. Because of this symmetry, their instantaneous algebraic sum at any instant is zero. Hence, the neutral current is also zero in a balanced system. Options (a), (b), and (d) are incorrect because the sum does not become maximum, minimum, or infinite; it cancels out exactly.
Poles of a network function are the values where the function becomes:
A)
Zero
B)
Infinite
C)
Constant
D)
Unity
A pole of a network function is a value of the complex frequency variable at which the function tends to infinity. In other words, poles are the roots of the denominator of the network function, provided they do not cancel with zeros. Hence the correct option is **(b) Infinite**.
- Zero corresponds to a zero of the function, not a pole.
- Constant and unity are not the defining behavior of poles.
The permittivity of free space is approximately:
A)
8.854 × 10-¹² F/m
B)
4π × 10-7 H/m
C)
3×108 m/s
D)
10-6 F/m
The permittivity of free space (vacuum permittivity), denoted by ε₀, is approximately 8.854 × 10⁻¹² farad per metre (F/m). Option (b) is the permeability of free space (μ₀), option (c) is the speed of light, and option (d) is not the correct value.
Digital instruments generally have:
A)
Lower accuracy
B)
Higher accuracy
C)
No sensitivity
D)
No stability
Digital instruments generally provide higher accuracy because they display measurements in discrete numerical form, reducing reading errors such as parallax and estimation errors that are common in analog instruments. Option (a) is incorrect because digital instruments are usually more accurate, not less. Option (c) is incorrect because digital instruments do have sensitivity to small changes in input. Option (d) is incorrect because digital instruments can be stable and are often designed for reliable readings.
What do you understand by reciprocal two-port network? Also derive the condition for the same in terms of ABCD parameters.
Permanent magnet moving coil (PMMC) instrument is used for:
A)
AC only
B)
DC only
C)
Both AC and DC
D)
High frequency signals
A PMMC (Permanent Magnet Moving Coil) instrument works on the interaction between the magnetic field of a permanent magnet and the current in the moving coil. The torque produced depends on the direction of current, so the deflection is suitable for direct current. For AC, the current reverses direction each half-cycle, causing the torque to reverse and the average deflection becomes nearly zero. Therefore, PMMC instruments are used for DC only. AC measurements require instruments like moving iron instruments or rectifier-type meters.
The steady-state response of a circuit refers to:
A)
Initial condition
B)
Transient state
C)
Long-term behavior
D)
Zero response
The steady-state response is the part of the circuit response that remains after all transient effects have died out. It describes the circuit’s long-term behavior as time becomes large.
- (a) Initial condition: This relates to the circuit state at the beginning, not steady state.
- (b) Transient state: Transients are the temporary changes before steady state is reached.
- (c) Long-term behavior: Correct, because steady-state response is what persists in the long run.
- (d) Zero response: Zero-input or zero-state response are specific components, not the definition of steady state.
So, the correct answer is long-term behavior.
Explain the properties of electric field inside conductors under electrostatic conditions.
A balanced delta connected load has, phase impedance = 10 Ω, line voltage = 400 V. Phase current is:
A)
23 A
B)
40 A
C)
69 A
D)
80 A
For a delta-connected load, phase voltage equals line voltage: Vph = VL = 400 V. The phase current is Iph = Vph / Zph = 400 / 10 = 40 A. However, the option that matches 40 A is (b), not (a). If the question intended line current, then IL = √3 × Iph = 1.732 × 40 ≈ 69 A, which matches option (c). Since the question specifically asks for phase current, the correct value is 40 A, so option (b) is correct.
Flow rate in pipes is commonly measured using:
A)
Flow meter
B)
Wattmeter
C)
Voltmeter
D)
Ammeter
Flow rate in pipes is measured using a flow meter, which is specifically designed to measure the quantity of fluid flowing through a pipe per unit time. A wattmeter measures electrical power, a voltmeter measures voltage, and an ammeter measures electric current, so these are not suitable for pipe flow measurement.
The Maxwell bridge is used for measurement of:
A)
Resistance
B)
Capacitance
C)
Inductance
D)
Frequency
The Maxwell bridge is an AC bridge used to measure an unknown inductance by comparing it with a known capacitance and resistances. It is especially suitable for measuring medium-quality inductors.
Why not the others?
- Resistance is measured by Wheatstone bridge.
- Capacitance is measured by De Sauty bridge or Schering bridge.
- Frequency is not the primary quantity measured by Maxwell bridge.
Therefore, the correct answer is Inductance.
Describe the working principle of Analog to Digital Converter.
Explain the measurement of capacitance using Schering bridge.
Explain superconductivity, its properties, and applications in electrical engineering.
Explain the operating principle of PMMC instruments.
The natural response of a circuit depends on:
A)
External excitation
B)
Stored energy in reactive elements
C)
Load resistance
D)
Source voltage
The natural response of a circuit is the response that occurs when all independent sources are removed. It is determined by the energy initially stored in reactive elements like inductors and capacitors. Therefore, the circuit’s natural response depends on stored energy in reactive elements, not on external excitation, load resistance, or source voltage.
Velocity of EM wave in free space is:
A)
3×106 m/s
B)
3×108 m/s
C)
3×1010 m/s
D)
3×104 m/s
The velocity of an electromagnetic wave in free space is equal to the speed of light, which is approximately 3 × 10^8 m/s. Option (a) is too low, option (c) is too high, and option (d) is far too low.
For the given network find the branch current in 8Ω and voltage across the 3Ω by applying KVL.
In a 3-phase power measurement by two wattmeter method, both the watt meters had identical readings. The power factor of the load was:
A)
Unity
B)
0.8 lagging
C)
0.8 leading
D)
zero
In the two-wattmeter method for a balanced 3-phase load, the wattmeter readings are equal when the load power factor angle is 0°. That means the current is in phase with the voltage, so the power factor is 1 (unity). For any lagging or leading power factor other than unity, the two readings will differ.
In free space, electromagnetic waves are:
A)
Longitudinal
B)
Transverse
C)
Circular
D)
Random
In free space, an electromagnetic wave has electric field (E) and magnetic field (B) oscillating perpendicular to each other and also perpendicular to the direction of propagation. Hence, it is a transverse wave. Longitudinal waves have oscillations parallel to propagation, which is not the case here. Circular and random do not describe the basic nature of EM waves in free space.
Ampere’s circuital law relates magnetic field intensity to:
A)
Electric potential
B)
Electric flux
C)
Electric current
D)
Magnetic flux
Ampere’s circuital law states that the line integral of magnetic field intensity around a closed path is equal to the electric current enclosed by that path. Therefore, it directly relates magnetic field intensity to electric current. Electric potential and electric flux are not involved in Ampere’s law, and magnetic flux is related more to Faraday’s law.
Mesh analysis is applicable to:
A)
Non-planar circuits only
B)
Planar circuits
C)
AC circuits only
D)
DC circuits only
Mesh analysis can be applied only to planar circuits, i.e., circuits that can be drawn on a plane without any branches crossing. This is because mesh currents are defined for the smallest loops in a planar network. It is not limited to AC or DC circuits; it works for both, as long as the circuit is planar. Non-planar circuits do not have well-defined meshes, so option (a) is incorrect.
Discuss ferromagnetism and ferrimagnetism with suitable examples and magnetic domain explanation.
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