Labour Officer • 2026 • Paper-II
The slip of 400 V, three phase, 4-pole induction motor when rotating at 1440 rpm is:
A)
2 per cent
B)
3 per cent
C)
4 per cent
D)
5 per cent
Option B is correct: 3 per cent.
Labour Officer • 2026 • Paper-II
Voltage sag in transmission systems is corrected by:
A)
Shunt capacitors
B)
Series reactors
C)
Load shedding
D)
Frequency adjustment
Option A is correct: Shunt capacitors.
Labour Officer • 2026 • Paper-II
Distribution factor for a winding having 3 slots/pole phase and a slot angle of 20° is:
A)
0.96
B)
1.0
C)
0.5
D)
0.707
Option A is correct: 0.96.
Labour Officer • 2026 • Paper-II
Steady-state error depends on:
A)
System type
B)
Input signal
C)
System gain
D)
All of these
Option D is correct: All of these.
Labour Officer • 2026 • Paper-II
The commutator in a DC machine acts as:
A)
Transformer
B)
Mechanical rectifier
C)
Amplifier
D)
Capacitor
Option B is correct: Mechanical rectifier.
Labour Officer • 2026 • Paper-II
The phenomenon of squirrel-cage motors sometime showing a tendency to run at a very low speed is known as:
A)
cogging
B)
crawling
C)
damping
D)
skewing
Option B is correct: crawling.
Labour Officer • 2026 • Paper-II
The skin effect in transmission lines causes:
A)
Increase in inductance
B)
Increase in resistance
C)
Decrease in capacitance
D)
Decrease in voltage
Option B is correct: Increase in resistance.
Labour Officer • 2026 • Paper-I
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).
Labour Officer • 2026 • Paper-I
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.
Labour Officer • 2026 • Paper-I
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.
Labour Officer • 2026 • Paper-I
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.
Labour Officer • 2026 • Paper-I
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.
Labour Officer • 2026 • Paper-I
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.
Labour Officer • 2026 • Paper-I
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.
Labour Officer • 2026 • Paper-I
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.
Labour Officer • 2026 • Paper-I
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.
Labour Officer • 2026 • Paper-I
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.
Labour Officer • 2026 • Paper-I
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.
Labour Officer • 2026 • Paper-I
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.
Labour Officer • 2026 • Paper-I
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.
Labour Officer • 2026 • Paper-I
Differentiate between accuracy, precision, resolution, and sensitivity in measurement systems.
Labour Officer • 2026 • Paper-I
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.
Labour Officer • 2026 • Paper-I
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.
Labour Officer • 2026 • Paper-I
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.
Labour Officer • 2026 • Paper-I
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.
