← Labour Officer
Past Questions — 2026
Negative feedback in amplifiers primarily helps to:
A)
Increase distortion
B)
Reduce bandwidth
C)
Stabilize gain
D)
Increase noise
Negative feedback in amplifiers is used to make the amplifier gain more stable and less sensitive to changes in component values, temperature, and supply variations. It also usually reduces distortion and noise while increasing bandwidth. Hence, the correct answer is (c) Stabilize gain. The other options are incorrect because negative feedback does not increase distortion, does not reduce bandwidth, and does not increase noise.
Delay in a system affects:
A)
Voltage
B)
Resistance
C)
Signal transmission
D)
Power
A delay in a system means the output occurs later than the input, which directly affects the timing of signal transmission. It does not specifically change voltage, resistance, or power by definition. Therefore, the correct answer is signal transmission.
At absolute zero temperature, all the valence electrons in an intrinsic semiconductor are:
A)
in the conduction band
B)
in the forbidden gap
C)
in the valance band
D)
free electrons
In an intrinsic semiconductor at absolute zero (0 K), there is no thermal energy available to excite electrons across the band gap. So all valence electrons remain bound in the valence band, and the conduction band is empty. They are not in the forbidden gap and not free electrons.
An active device is:
A)
Resistor
B)
Capacitor
C)
Transistor
D)
Inductor
An active device is one that can control current and provide amplification or switching action, usually requiring an external power source. A transistor is an active semiconductor device used for amplification and switching. Resistor, capacitor, and inductor are passive devices because they do not provide power gain or amplification.
Mobility of an electron in a semiconductor:
A)
decreases as the temperature increases
B)
increases as the temperature increases
C)
has no effect on conductivity
D)
is independent of temperature
Electron mobility in a semiconductor generally decreases as temperature increases because lattice vibrations (phonons) become stronger at higher temperatures. These vibrations scatter electrons more frequently, reducing their drift mobility. Therefore, option (a) is correct. Option (b) is opposite to the usual behavior, option (c) is wrong because mobility directly affects conductivity, and option (d) is incorrect because mobility is temperature-dependent.
Discuss the properties and characteristics of piezoelectric materials.
A system which is linear is said to obey the rules of:
A)
Scaling
B)
Additivity
C)
Both scaling and additivity
D)
Homogeneity
A linear system must satisfy two basic properties: additivity and homogeneity (scaling). Additivity means the response to a sum of inputs equals the sum of the responses, and homogeneity means scaling the input scales the output by the same factor. Therefore, a linear system obeys both scaling and additivity. Option (d) is only one part of linearity, not the complete rule.
In a series RLC circuit, at resonant frequency:
A)
current is minimum
B)
voltage across C is maximum
C)
impedance is maximum
D)
current is maximum
In a series RLC circuit at resonance, the inductive reactance equals the capacitive reactance (XL = XC), so they cancel each other. The circuit impedance becomes minimum and equal to only the resistance (Z = R). Since current is I = V/Z, the current is therefore maximum at resonance. Hence, (d) is correct. Option (a) is wrong because current is not minimum; option (c) is wrong because impedance is minimum, not maximum. Option (b) can be true in the sense that capacitor voltage may be high at resonance, but the key standard answer for a series RLC circuit is that current is maximum.
After VDS reaches pinch-off value VP in a JFET, drain current ID becomes:
A)
zero
B)
low
C)
saturated
D)
reversed
In a JFET, when the drain-source voltage VDS reaches the pinch-off voltage VP, the channel narrows enough that the drain current ID stops increasing significantly with further increase in VDS. It enters the saturation region and remains nearly constant. Hence, the drain current becomes saturated. Option (a) is wrong because current does not become zero, and (d) is wrong because current does not reverse.
The number of branches incident at the node of a graph is called:
A)
degree of the node
B)
order of the node
C)
status of the node
D)
number of the node
In graph theory, the number of branches (edges) incident at a node (vertex) is called the degree of that node. The other options are not standard graph-theory terms: order usually refers to the number of vertices in a graph, and status/number of the node are not used for this definition.
Which of the following is a stable system?
A)
y(t) = t x(t)
B)
y(t) = t^2 x(t)
C)
y(t) = e^t x(t)
D)
y(t) = e^-t x(t)
A system is BIBO stable if every bounded input produces a bounded output. If x(t) is bounded, then multiplying it by a factor that remains bounded for all t gives a bounded output. Among the options, e^-t is the only factor that does not grow without bound in the stable direction typically intended in such MCQs. The terms t, t^2, and e^t grow without bound, so (a), (b), and (c) are unstable. Hence the intended answer is (d).
The circuit which satisfies Reciprocity Theorem is called?
A)
Short circuit
B)
Open circuit
C)
Linear circuit
D)
Non-linear circuit
The Reciprocity Theorem applies to **linear, bilateral networks**. Such a circuit is commonly called a **linear circuit**. In these circuits, interchanging the positions of source and response does not change the current/voltage relationship.
- **(a) Short circuit**: This is only a circuit condition, not the type required for reciprocity.
- **(b) Open circuit**: Also just a circuit condition, not the required category.
- **(c) Linear circuit**: Correct, because reciprocity holds for linear networks.
- **(d) Non-linear circuit**: Incorrect, since reciprocity generally does not apply to non-linear circuits.
The system y(n) = sin[x(n)] is:
A)
stable
B)
BIBO stable
C)
unstable
D)
none of the above
A system is BIBO stable if every bounded input produces a bounded output. Here, the output is y(n) = sin[x(n)]. Since the sine function always stays within the range [-1, 1] for any real input, the output remains bounded whenever the input is bounded. Therefore, the system is BIBO stable. Option (a) is too vague, (c) is incorrect because the output cannot blow up, and (d) is incorrect.
Relative permeability of a paramagnetic material is:
A)
infinite
B)
one
C)
little more than one
D)
less than one
For a paramagnetic material, the magnetic susceptibility is small and positive. Since relative permeability \(\mu_r = 1 + \chi_m\), its value is slightly greater than 1. Hence the correct choice is (c) little more than one.
Why others are incorrect: (a) infinite is for an ideal superconductor, not paramagnetic material; (b) one is approximately true for non-magnetic materials like vacuum/air, but paramagnetic materials are slightly above 1; (d) less than one is characteristic of diamagnetic materials.
The hybrid parameter h11 is called:
A)
short circuit input impedance
B)
short circuit forward current gain
C)
open circuit reverse voltage gain
D)
open circuit output admittance
In the h-parameter (hybrid) model of a two-port network, h11 = V1/I1 with the output port short-circuited, so h11 represents the short-circuit input impedance. By definition, h12 is open-circuit reverse voltage gain, h21 is short-circuit forward current gain, and h22 is open-circuit output admittance. Therefore, the correct answer is (a).
A transistor is in active region when:
A)
IC = βIB
B)
IC = βIE
C)
IC = IC
D)
IC = IB
In the active region of a BJT, the collector current is controlled by the base current and is approximately equal to β times the base current: IC = βIB. This is the standard current relation used for transistor amplification. Option (b) is incorrect because IC is not βIE; emitter current is related by IE = IC + IB. Option (c) is a meaningless identity, and option (d) is not the active-region relation.
Norton equivalent current is:
A)
Open circuit current
B)
Short circuit current
C)
Peak current
D)
RMS current
Norton’s theorem states that any linear two-terminal network can be replaced by an equivalent current source in parallel with a resistance. The Norton equivalent current is the current that flows when the output terminals are short-circuited, so it is the short-circuit current. Open-circuit current is not the Norton current, and peak/RMS current are unrelated general AC quantities.
Inductive reactance increases with:
A)
Decreasing frequency
B)
Constant frequency
C)
Increasing frequency
D)
Voltage
Inductive reactance is given by X_L = 2\pi f L, where f is frequency and L is inductance. Since X_L is directly proportional to frequency, it increases when frequency increases. Therefore, the correct option is (c). Option (a) is wrong because decreasing frequency reduces inductive reactance. Option (b) would keep reactance unchanged. Option (d) voltage does not determine inductive reactance.
Ceramic resonators are used for:
A)
Amplification
B)
Power supply
C)
Frequency control
D)
Rectification
Ceramic resonators are electronic components used to provide a stable resonant frequency in circuits, so they are mainly used for frequency control and timing applications. They are not used for amplification, power supply, or rectification, which are performed by different circuit components.
Hard superconductors observe:
A)
breakdown by Silsbee’s rule
B)
incomplete Meissner effect
C)
high critical field and transition temperature
D)
all of these
Hard superconductors are type-II superconductors. They are characterized by: (1) very high critical magnetic fields, (2) relatively high transition temperature in many practical materials, and (3) incomplete Meissner effect because magnetic flux can partially penetrate in the mixed state. Silsbee’s rule is associated with the limiting current/field behavior in superconductors and is relevant in describing breakdown conditions. Hence, all given statements are taken as features observed in hard superconductors.
Quartz crystal oscillator works on:
A)
Magnetic effect
B)
Thermal effect
C)
Piezoelectric effect
D)
Optical effect
A quartz crystal oscillator uses the piezoelectric effect of quartz. When an electric field is applied, the crystal mechanically vibrates, and these vibrations are used to generate a stable oscillation frequency. The other options are incorrect because quartz oscillators do not operate based on magnetic, thermal, or optical effects.
A network which contains one or more than one source of e.m.f. is known as:
A)
linear network
B)
non-linear network
C)
passive network
D)
active network
A network containing one or more sources of e.m.f. (like a voltage source or current source) can supply energy to the circuit, so it is called an active network. A passive network contains no source of e.m.f. and only absorbs or stores energy. Linear and non-linear describe the relationship between voltage and current, not whether the network has sources.
A general purpose diode is more likely to suffer Avalanche breakdown rather than Zener breakdown because:
A)
its leakage current is small
B)
it has strong covalent bonds
C)
it is lightly doped
D)
it has low reverse resistance
A general-purpose diode is usually lightly doped, so its depletion region is wider. In a wide depletion region, the electric field needed for breakdown is reached at a higher reverse voltage, and the dominant breakdown mechanism is avalanche breakdown rather than Zener breakdown. Zener breakdown typically occurs in heavily doped diodes with a thin depletion layer. The other options do not determine the breakdown mechanism.
Determine the inverse Z-transform of X(z) = z^2 / (z^2 - z + 0.5).
Compute the ABCD-parameters of a two-port network if the y-parameters are: y11 = 0.6 mho, y12 = 0.3 mho, y21 = y22 = -0.2 mho.