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Past Questions
A 50 Hz RLC circuit has, L = 0.2 H, C = 100 μF. The resonance frequency is approximately:
A)
35 Hz
B)
50 Hz
C)
70 Hz
D)
100 Hz
For a resonant RLC circuit, the resonance frequency is
f0 = 1 / (2π√(LC))
Given:
L = 0.2 H
C = 100 μF = 100 × 10^-6 F = 10^-4 F
So,
LC = 0.2 × 10^-4 = 2 × 10^-5
√(LC) ≈ √(2 × 10^-5) ≈ 4.47 × 10^-3
Therefore,
f0 ≈ 1 / (2π × 4.47 × 10^-3) ≈ 35.6 Hz
So the nearest option is 35 Hz.
The other options are not close to the calculated resonance frequency.
A network with no energy storage elements exhibits:
A)
Transient response
B)
Steady-state response only
C)
Oscillatory response
D)
Resonant response
A network with no energy storage elements means it has only resistive elements, with no inductors or capacitors. Since transient behavior arises due to energy storage in L and C, such a network cannot exhibit transient response. Therefore, it shows only steady-state response. Options (a), (c), and (d) require reactive elements, so they are incorrect.
Induction type single phase energy meters measure electric energy in:
A)
kW
B)
Wh
C)
kWh
D)
None of the above
An induction type single-phase energy meter measures electrical energy consumed over time, which is expressed in kilowatt-hour (kWh). It does not measure instantaneous power in kW, and Wh is a smaller unit but the standard billing unit is kWh. Hence, the correct answer is kWh.
The intrinsic impedance of free space is approximately:
A)
50 Ω
B)
100 Ω
C)
377 Ω
D)
500 Ω
The intrinsic impedance of free space is given by η₀ = √(μ₀/ε₀), where μ₀ is the permeability of free space and ε₀ is the permittivity of free space. Substituting the standard values gives η₀ ≈ 376.7 Ω, which is approximately 377 Ω. Hence, option (c) is correct. The other values are far from the standard intrinsic impedance of free space.
The equivalent resistance between two nodes of a circuit can be most easily determined using:
A)
Mesh analysis
B)
Nodal analysis
C)
Superposition theorem
D)
Maximum power transfer theorem
The equivalent resistance between two nodes is most easily found by applying a test source and using nodal analysis. In nodal analysis, the current-voltage relations at nodes make it straightforward to compute the voltage-to-current ratio, i.e., the equivalent resistance. Mesh analysis can also be used in some cases, but it is generally less direct for finding resistance between two nodes. Superposition theorem is for analyzing circuits with multiple sources, and maximum power transfer theorem is unrelated to equivalent resistance determination.
Explain magnetization and classify magnetic materials.
Define natural response of a circuit and explain with RL example.
The temperature below which a material becomes superconducting is called:
A)
Curie temperature
B)
Critical temperature
C)
Transition temperature
D)
Melting temperature
A material enters the superconducting state only below a specific temperature called the critical temperature (Tc). This is the standard term used in superconductivity. Curie temperature relates to ferromagnetism, melting temperature is the solid-to-liquid phase change point, and transition temperature is a more general term but in this context the correct and precise answer is critical temperature.
Attenuation constant represents:
A)
Phase change
B)
Signal loss
C)
Wave velocity
D)
Frequency
The attenuation constant of a transmission line indicates how much the signal amplitude decreases as it propagates along the line. In other words, it represents signal loss. Phase change is represented by the phase constant, wave velocity is related to propagation constant/phase constant, and frequency is a separate signal parameter.
Piezoelectric transducers are commonly used to measure:
A)
Displacement
B)
Acceleration
C)
Temperature
D)
Voltage
Piezoelectric transducers generate an electric charge when mechanical stress is applied. They are commonly used in accelerometers to measure acceleration, vibration, and dynamic force. Displacement is usually measured by devices like LVDT or potentiometric transducers, temperature by thermocouples/RTDs, and voltage by voltmeters or electronic measuring circuits.
Precision refers to:
A)
Closeness to true value
B)
Repeatability of measurement
C)
Power measurement
D)
Voltage measurement
Precision means how close repeated measurements are to each other, i.e., repeatability or consistency. It is different from accuracy, which means closeness to the true value. So (a) describes accuracy, not precision. Options (c) and (d) are unrelated to the definition of precision.
Differentiate between accuracy, precision, resolution, and sensitivity in measurement systems.
An RC circuit has, R = 10 kΩ, C = 10 μF. Time constant is:
A)
0.01 s
B)
10 s
C)
1 s
D)
0.1 s
For an RC circuit, the time constant is \(\tau = RC\). Here, \(R = 10\,k\Omega = 10{,}000\,\Omega\) and \(C = 10\,\mu F = 10 \times 10^{-6}\,F\). So, \(\tau = 10{,}000 \times 10 \times 10^{-6} = 0.1\,s\). Hence, the correct answer is (d) 0.1 s.
Maxwell added displacement current to modify:
A)
Coulomb’s law
B)
Gauss’s law
C)
Ampere’s law
D)
Faraday’s law
Maxwell introduced the concept of displacement current to modify Ampere’s law, because the original form could not account for changing electric fields in regions like a charging capacitor. With this correction, the law becomes consistent with charge conservation and completes Maxwell’s equations. Coulomb’s law, Gauss’s law, and Faraday’s law were not the ones modified by displacement current.
Energy stored in electric field is proportional to:
A)
E²
B)
H²
C)
EH
D)
1/E
The energy density stored in an electric field is given by u = 1/2 \u03b5E², where \u03b5 is the permittivity of the medium. Hence, the stored energy is proportional to E². Option (b) H² refers to magnetic field energy, option (c) EH is not the standard dependence for electric field energy, and option (d) 1/E is incorrect.
The boundary condition for the tangential component of electric field is:
A)
Discontinuous
B)
Infinite
C)
Continuous
D)
Zero
The tangential component of the electric field must be continuous across a boundary in electrostatics, provided there is no time-varying magnetic field inducing a discontinuity. From Maxwell’s equations, the line integral of **E** around a tiny loop straddling the boundary gives the condition that the difference in tangential components on the two sides is zero. Hence, the tangential component is **continuous**.
Why the other options are wrong:
- **Discontinuous**: Not generally true for the tangential component of **E**.
- **Infinite**: Electric field components do not become infinite just because of a boundary.
- **Zero**: Only the tangential component on a perfect conductor surface is zero, not at all boundaries.
Explain the Hall effect. A semiconductor plate carries a current of 5 A in a magnetic field of 0.2 T. If the Hall voltage is 2 mV and thickness is 1 mm, calculate the Hall coefficient.
A single-phase kilowatt hour meter makes 500 revolutions per kilowatt hour. It is found on testing as making 40 revolutions in 58.1 seconds at 5KW full load. Find the percentage error.
State Ohm’s law and its limitations. An electric heater draws 8A from 250V supply. What is the power rating? Find the resistance of the heater element.
Which impurity produces n-type semiconductor?
A)
Trivalent impurity
B)
Pentavalent impurity
C)
Divalent impurity
D)
Monovalent impurity
An n-type semiconductor is formed when a pure semiconductor like silicon or germanium is doped with a pentavalent impurity such as phosphorus, arsenic, or antimony. These atoms have 5 valence electrons, so after forming four covalent bonds with the host atoms, one extra electron becomes available for conduction. Hence the majority charge carriers are electrons. Trivalent impurities produce p-type semiconductors, while divalent and monovalent impurities do not produce n-type semiconductors.
Which of the following is a good insulating material?
A)
Copper
B)
Aluminum
C)
Mica
D)
Silver
Mica is a good insulating material because it has very high electrical resistance and can withstand high temperatures. Copper, aluminum, and silver are all good conductors of electricity, so they are not suitable as insulators.
Ceramic materials are generally:
A)
Good conductors
B)
Good insulators
C)
Magnetic materials
D)
Superconductors
Ceramic materials typically have strong ionic/covalent bonds and very few free charge carriers, so they do not conduct electricity well. Hence, they are generally used as electrical insulators. The other options are incorrect because ceramics are not generally good conductors, magnetic materials, or superconductors.
Polarization in a dielectric occurs due to:
A)
Free electrons
B)
Alignment of dipoles
C)
Magnetic flux
D)
Electric current
Polarization in a dielectric means the slight shift or orientation of positive and negative charges within the material when an electric field is applied. In many dielectrics, this happens mainly by alignment of existing dipoles. Free electrons are not responsible because dielectrics do not have freely moving charge carriers like conductors. Magnetic flux and electric current are unrelated to dielectric polarization.
The forbidden energy gap of silicon at room temperature is approximately:
A)
0.67 eV
B)
1.1 eV
C)
3 eV
D)
5 eV
The forbidden energy gap (band gap) of silicon at room temperature is approximately 1.1 eV. Silicon is a semiconductor, and its band gap is much smaller than that of insulators, but larger than that of conductors. Among the options, 0.67 eV is too low for silicon, while 3 eV and 5 eV are far too high.
If the critical field for a superconductor at 0 K is 1000 G, what is the critical field at a temperature T=Tc/2?
A)
500 G
B)
250 G
C)
750 G
D)
1000 G
For a superconductor, the critical field varies with temperature as Hc(T) = Hc(0) [1 - (T/Tc)^2].
Given Hc(0) = 1000 G and T = Tc/2:
Hc = 1000 [1 - (1/2)^2] = 1000 [1 - 1/4] = 1000 × 3/4 = 750 G.
But the options show 750 G as option (c), so the correct answer is (c), not (b).