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Past Questions
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.
What do you understand by reciprocal two-port network? Also derive the condition for the same in terms of ABCD parameters.
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.
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.
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.
Explain time-varying electromagnetic fields and displacement current.
Derive the expression for the electric field intensity due to an infinite line charge using Coulomb’s law.
Find the current supplied by the battery for the figure shown in the paper.
A wire of length 1m has a resistance of 2Ω. What is the resistance of the second wire, whose specific resistance is double that of the first, if the length of wire is 3m and the diameter is double that of the first?
State Maximum Power Transfer theorem and derive its condition.
Define transducers and explain working of resistive transducers with examples.
Which of the following is a ferromagnetic material?
A)
Copper
B)
Aluminium
C)
Iron
D)
Silver
Ferromagnetic materials are strongly attracted by magnetic fields and can be permanently magnetized. Iron is a classic ferromagnetic material. Copper, aluminium, and silver are not ferromagnetic: copper and silver are diamagnetic, while aluminium is paramagnetic.
A frequency counter counts 5000 pulses in 0.1 s. The frequency of the signal is:
A)
5 kHz
B)
10 kHz
C)
50 kHz
D)
500 kHz
Frequency is the number of pulses per second. Here, 5000 pulses are counted in 0.1 s, so frequency = 5000 / 0.1 = 50000 Hz = 50 kHz. Therefore, the correct option is (c).
The curl of magnetic field equals:
A)
∂B/∂t
B)
J + ∂D/∂t
C)
∇·E
D)
∇·D
This is Ampere-Maxwell law in differential form: ∇ × B = μ₀J + μ₀ε₀(∂E/∂t), or equivalently ∇ × H = J + ∂D/∂t. Among the given options, the expression matching the curl relation for magnetic field is J + ∂D/∂t. Option (a) is related to Faraday’s law, while (c) and (d) are divergence relations, not curl relations.
Ferrites are commonly used in:
A)
High-frequency transformers
B)
Electric heaters
C)
DC generators
D)
Lamps
Ferrites are magnetic ceramic materials with high electrical resistivity and low eddy current losses, so they work well at high frequencies. That is why they are commonly used in high-frequency transformers and inductors. Electric heaters, DC generators, and lamps are not typical applications of ferrites.
Data acquisition system mainly consists of:
A)
Sensors
B)
Signal conditioning
C)
ADC and processor
D)
All of the above
A data acquisition (DAQ) system generally includes sensors to measure physical quantities, signal conditioning circuits to prepare the signal for processing, and an ADC (analog-to-digital converter) with a processor/computer to convert, process, and store the data. Since all three are essential parts of a typical DAQ system, the correct answer is All of the above.
The SI unit of electric flux density D is:
A)
V/m
B)
C/m²
C)
Wb/m²
D)
A/m
Electric flux density D is also called electric displacement. From Gauss’s law, D = Q/A, so its SI unit is coulomb per square metre (C/m²). Option (a) V/m is the unit of electric field, (c) Wb/m² is magnetic flux density, and (d) A/m is the unit of magnetic field intensity.
Hysteresis loss is undesirable in:
A)
Permanent magnets
B)
Transformer cores
C)
Recording tapes
D)
Magnetic switches
Hysteresis loss occurs when a magnetic material is repeatedly magnetized and demagnetized. This loss is undesirable in transformer cores because transformers work with alternating magnetic flux, so repeated cycling causes energy loss as heat and reduces efficiency. In contrast, permanent magnets need materials with high hysteresis, recording tapes rely on magnetic properties for storing data, and magnetic switches are not primarily affected in the same way as transformer cores.
Network synthesis is the process of:
A)
Simplifying circuits
B)
Designing networks from transfer function
C)
Measuring voltage
D)
Measuring current
Network synthesis means constructing or designing an electrical network that realizes a given desired function, usually a transfer function, impedance, admittance, or system response. It is not about simply simplifying circuits, and it is unrelated to measuring voltage or current. Therefore, the correct option is (b).
Strain gauge transducers are used to measure:
A)
Pressure and force
B)
Temperature
C)
Light intensity
D)
Magnetic field
A strain gauge measures strain, i.e., the deformation of a body under load. Since strain is produced by applied force, strain gauge transducers are commonly used in devices like load cells and pressure sensors to measure force and pressure. Temperature, light intensity, and magnetic field are measured by different types of transducers, not strain gauges.
Magnetic permeability indicates:
A)
Electrical resistance
B)
Ability to conduct electricity
C)
Ability to support magnetic field
D)
Thermal conductivity
Magnetic permeability is a measure of how easily a material can support or allow the formation of a magnetic field within it. A higher permeability means the material is more easily magnetized. The other options are unrelated: electrical resistance is opposition to electric current, ability to conduct electricity refers to electrical conductivity, and thermal conductivity is about heat transfer.
Hall effect is used to determine:
A)
Carrier concentration
B)
Carrier mobility
C)
Type of semiconductor
D)
All of these
The Hall effect is used to find several key semiconductor parameters: (1) the sign of Hall coefficient tells the type of semiconductor (n-type or p-type), (2) the Hall coefficient helps determine carrier concentration, and (3) combining Hall coefficient with conductivity gives carrier mobility. Therefore, all the listed options are correct.
Kelvin double bridge is used for measuring:
A)
High resistance
B)
Low resistance
C)
Medium resistance
D)
Insulation resistance
A Kelvin double bridge is designed to measure very low resistances accurately. It eliminates the effect of lead and contact resistances, which become significant when the resistance under test is small. Therefore, it is used for measuring low resistance. High resistance is measured by other methods such as a megohmmeter or loss of insulation methods, and medium resistance is generally measured by Wheatstone bridge-type arrangements.
At resonance in a series RLC circuit, impedance is:
A)
Minimum
B)
Maximum
C)
Zero
D)
Infinite
In a series RLC circuit at resonance, the inductive reactance equals the capacitive reactance (XL = XC). These cancel each other, so the circuit impedance becomes only the resistance R, which is the smallest possible value for that circuit. Hence, impedance is minimum. It is not zero because resistance remains present, and it is not maximum or infinite in a series circuit at resonance.
The household energy meter is:
A)
an indicating instrument
B)
a recording instrument
C)
an integrating instrument
D)
none of the above
A household energy meter measures the total electrical energy consumed over time in kWh. Instruments that measure the total quantity over a period are called integrating instruments. An indicating instrument shows the instantaneous value, and a recording instrument continuously records the variation with time. Therefore, the correct answer is an integrating instrument.