At a PN-junction, electrons diffuse from the N-region to the P-region because of the

A) difference in carrier concentration

Which of the following defines base transportation factor of an NPN transistor?

A) The ratio of the number of electrons arriving at collector to the number of emitted electrons

In a BJT amplifier, the Q-point is stabilized by

C) Changing the base current to keep $I_C$ and $V_{CE}$ constant

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100 questions with answersProvisional key(Cat.No. 333/2019)

Junior Instructor (Electronic Mechanic) - Industrial Training question paper 2023

Date of test: 13-06-2023
Question paper code: 81/2023/OL
Questions: 100
Answer key: Provisional Answer Key
Exam mode: Online (computer based)

Provisional key. Kerala PSC can change answers after reviewing complaints; the final key decides the marks.

See questions with answers Practise as a mock test

Source: Kerala PSC (keralapsc.gov.in) · official document· Last updated 25 Sept 2026· How we check content

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All 100 questions with answers

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1.
Two resistors of the same value are connected in parallel and a 100V supply is connected across the terminals. If the total current taken is 10A, what is the value of each resistor?
Show answer and explanation
Answer: C —
20Ω
Total resistance $R_t = \frac{V}{I} = \frac{100}{10} = 10\Omega$ . Since two equal resistors are in parallel, $R = 2 \times R_t = 20\Omega$ .
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2.
Select the colour code for a resistor of value 680kΩ with ±5% tolerance from the given options.
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Answer: D —
Blue, Grey, Yellow and Gold
680kΩ = 68 $\times 10^4$ . Colour code: 6 (Blue), 8 (Grey), 4 (Yellow), 5% (Gold).
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3.
The reactance of a capacitor ________ with increase in frequency of the current flowing through it.
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Answer: B —
decreases
Capacitive reactance $X_C = \frac{1}{2\pi fC}$ . As frequency $f$ increases, $X_C$ decreases.
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4.
The quality factor 'Q' of a coil at resonance is 100. If the resistance of the coil is 10Ω, what is the value of it's reactance at resonance?
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Answer: B —
1kΩ
$Q = \frac{X_L}{R}$ . Therefore, $X_L = Q \times R = 100 \times 10 = 1000\Omega = 1k\Omega$ .
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5.
Two capacitors 100μF each, connected in parallel are then connected in series with a third capacitor of value 200μF. What is the effective capacitance of the entire combination?
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Answer: C —
100μF
Parallel combination: $100\mu F + 100\mu F = 200\mu F$ . Series with $200\mu F$ : $\frac{200 \times 200}{200 + 200} = 100\mu F$ .
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6.
Which of the following devices exhibits negative resistance?
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Answer: D —
Tunnel diode
A tunnel diode is a semiconductor diode that exhibits negative resistance in its operating range.
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7.
Which breakdown mechanism is likely to take place in a heavily doped PN junction diode?
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Answer: B —
Zener breakdown
Zener breakdown occurs in heavily doped junctions due to high electric field intensity.
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8.
Which of the following statements are not correct for a JFET? (i) It is a bipolar device (ii) It has high input impedance (iii) It is a current controlled device (iv) Small in size compared to BJT
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Answer: D —
(i) and (iii)
JFET is a unipolar device and is voltage-controlled, not current-controlled.
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9.
The arrow pointer on a transistor symbol indicates
Show answer and explanation
Answer: C —
direction of hole current
The arrow on the emitter indicates the direction of conventional current flow, which is the direction of hole current.
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10.
For the operation of n-channel E-MOSFET, the gate voltage must be
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Answer: C —
high positive
An enhancement-mode MOSFET requires a positive gate-to-source voltage greater than the threshold voltage to create a channel.
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11.
Which of the following is an adjustable voltage regulator IC?
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Answer: B —
LM317
LM317 is a popular adjustable positive voltage regulator IC.
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12.
The forbidden energy gap of Silicon at room temperature is
Show answer and explanation
Answer: A —
1.12 eV
The band gap energy of silicon at room temperature ( $300\text{ K}$ ) is approximately $1.12\text{ eV}$ .
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13.
A heavily doped p-type semiconductor material is
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Answer: C —
electrically neutral
Like any semiconductor material, extrinsic p-type material is overall electrically neutral because the number of protons equals the number of electrons.
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14.
At a PN-junction, electrons diffuse from the N-region to the P-region because of the
Show answer and explanation
Answer: A —
difference in carrier concentration
Diffusion is driven by the concentration gradient of charge carriers across the junction.
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15.
Which of the following statements about the leakage current in a semiconductor diode are correct? (i) Created due to the flow of majority carriers. (ii) Remains the same irrespective of the changes in biasing voltage. (iii) Varies with variation in temperature. (iv) Of the order of microamperes in silicon and nanoamperes in germanium
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Answer: C —
(ii) and (iii)
Leakage current is due to minority carriers, remains relatively constant with reverse bias voltage, and is highly temperature-dependent.
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16.
Which of the following defines base transportation factor of an NPN transistor?
Show answer and explanation
Answer: A —
The ratio of the number of electrons arriving at collector to the number of emitted electrons
Base transportation factor is defined as the ratio of carriers reaching the collector to those injected by the emitter into the base.
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17.
Which transistor configuration has very high input resistance and very low output resistance?
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Answer: C —
Common Collector
Common Collector (emitter follower) configuration provides very high input impedance and very low output impedance.
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18.
The current gain $\alpha$ of a transistor is 0.99. What is the value of its $\beta$ ?
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Answer: B —
99
$\beta = \frac{\alpha}{1 - \alpha} = \frac{0.99}{1 - 0.99} = \frac{0.99}{0.01} = 99$ .
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19.
In a BJT amplifier, the Q-point is stabilized by
Show answer and explanation
Answer: C —
Changing the base current to keep $I_C$ and $V_{CE}$ constant
Stabilization circuits adjust base current automatically to counteract variations in temperature and transistor parameters, maintaining constant $I_C$ and $V_{CE}$ .
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20.
Factors that affect the lower cut-off frequency of a RC coupled CE amplifier are (i) Ineffective bypassing of emitter bypass capacitors (ii) Bypassing effect of junction capacitances (iii) Signal loss across coupling capacitors (iv) Loading effect of subsequent stages
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Answer: D —
(i) and (iii)
Lower cut-off frequency is primarily determined by coupling capacitors and emitter bypass capacitors whose reactance increases at low frequencies.
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21.
Which coupling scheme is preferred for a multistage amplifier used to amplify signals below 10 Hz?
Show answer and explanation
Answer: A —
Direct coupling
Direct coupling is used for very low frequency (down to DC) signals because capacitors block DC and low frequencies.
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22.
Which of the following oscillator circuits is suitable to generate audio frequency signals?
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Answer: D —
Wien bridge oscillator
Wien bridge oscillator is widely used for generating audio frequency range signals due to its excellent frequency stability and low distortion.
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23.
Which of the following circuit can be used as a memory element?
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Answer: B —
Bistable Multivibrator
Bistable multivibrator has two stable states and can store 1 bit of binary information, acting as a basic memory element.
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24.
The differential mode gain of an op-amp is $10^5$ . If the common mode gain is 0.1, what is its CMRR?
Show answer and explanation
Answer: D —
$10^6$
CMRR = $\frac{A_d}{A_c} = \frac{10^5}{0.1} = 10^6$ . In dB, $20 \log_{10}(10^6) = 120\text{ dB}$ .
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25.
Which of the following is not the characteristic of an ideal op-amp?
Show answer and explanation
Answer: B —
Infinite output resistance
An ideal op-amp has zero output resistance, not infinite output resistance.
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26.
The electrolyte used in dry cell?
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Answer: A —
Ammonium chloride
Ammonium chloride paste is commonly used as the electrolyte in a standard zinc-carbon dry cell.
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27.
The specific gravity of the electrolyte in a lead acid battery can be measured using _________.
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Answer: C —
Hydrometer
A hydrometer is used to measure the specific gravity (density) of the electrolyte, indicating the state of charge of a lead-acid battery.
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28.
Conventionally the energy stored in a battery is measured in __________.
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Answer: B —
Ampere - Hour
Battery capacity and stored energy are commonly rated in Ampere-hours (Ah).
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29.
In a full wave rectifier if the input signal frequency is 50 Hz, find the output signal frequency?
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Answer: C —
100 Hz
The output frequency of a full-wave rectifier is twice the input frequency ( $2 \times 50\text{ Hz} = 100\text{ Hz}$ ).
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30.
Based on the input cycles utilized, the rectifiers can be classified as __________.
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Answer: D —
Both (1) and (2)
Rectifiers are broadly classified into half-wave and full-wave rectifiers based on whether they utilize half or full cycles of the input AC.
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31.
The following symbol represents _________ in an electrical system.
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Answer: B —
Inverter
An inverter symbol converts DC to AC.
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32.
Choose the disadvantage of SMPS:
Show answer and explanation
Answer: B —
Noise exist due to high frequency switching
SMPS generates high-frequency electromagnetic noise/interference due to rapid switching.
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33.
The regulated DC power supply consists of ________.
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Answer: D —
All the above
A regulated DC power supply comprises a transformer, rectifier, filter circuit, and a voltage regulator.
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34.
The instruments used for critical load during temporary power failure occur is ________.
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Answer: A —
UPS
An Uninterruptible Power Supply (UPS) provides emergency power to critical loads instantly when input power source fails.
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35.
What is used to neutralize a spilled electrolyte from a lead acid battery?
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Answer: D —
Baking soda
Baking soda (sodium bicarbonate) is a mild base used to neutralize sulfuric acid spills from lead-acid batteries.
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36.
The self inductance of two coils is 16 mH and 4 mH respectively. If the coefficient of coupling is 0.7, the mutual inductance between the coils is,
Show answer and explanation
Answer: B —
5.6 mH
Mutual inductance $M = k \sqrt{L_1 L_2} = 0.7 \times \sqrt{16\text{ mH} \times 4\text{ mH}} = 0.7 \times \sqrt{64} = 0.7 \times 8 = 5.6\text{ mH}$ .
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37.
The voltage and current in ac circuit is represented by $v = \sin(\omega t + 30^\circ)$ and $i = \sqrt{2}\sin(\omega t - 45^\circ)$ . The power factor angle of the circuit is
Show answer and explanation
Answer: D —
$75^\circ$
Phase angle of voltage $\theta_v = 30^\circ$ , phase angle of current $\theta_i = -45^\circ$ . The phase difference (power factor angle) $\phi = \theta_v - \theta_i = 30^\circ - (-45^\circ) = 75^\circ$ .
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38.
What is the true condition for maximum power transform from source to load as per maximum power transform theorem?
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Answer: A —
Source resistance is equal to load resistance
Maximum power transfer theorem states that maximum power is transferred when the load resistance equals the internal resistance of the source ( $R_L = R_S$ ).
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39.
Power factor of a parallel resonant circuit is
Show answer and explanation
Answer: C —
Unity
At parallel resonance, the circuit appears purely resistive, so the power factor is unity.
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40.
Which of the following instruments measure RMS value of unknown current?
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Answer: D —
Both (2) and (3)
Both Electrodynamic and Moving Iron instruments respond to the square of current ( $I^2$ ), thereby measuring the true RMS value for both AC and DC.
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41.
The energy meter installed near the main switch in residences and other locations is,
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Answer: D —
An integrating type instrument
An energy meter is an integrating instrument that measures total electric energy consumed over a period of time.
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42.
The extension range of an ammeter and voltmeter can be made represented by,
Show answer and explanation
Answer: B —
Using shunt and multiplier
Range of an ammeter is extended using a parallel shunt resistor, and a voltmeter range is extended using a series multiplier resistor.
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43.
In a moving iron instrument which is spring controlled, a current of 5A produces a deflection of $60^\circ$ . What will be the deflection when a current of 2A is flowing through the coil of the instrument?
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Answer: A —
$9.6^\circ$
Deflection in a spring-controlled moving iron instrument is proportional to the square of current ( $\theta = k I^2$ ). Thus, $\frac{\theta_2}{\theta_1} = \left(\frac{I_2}{I_1}\right)^2 \Rightarrow \theta_2 = 60^\circ \times \left(\frac{2}{5}\right)^2 = 60 \times \frac{4}{25} = 9.6^\circ$ .
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44.
According to Faraday's law of electromagnetic induction,
Show answer and explanation
Answer: C —
Electric field is produced by time varying magnetic flux
Faraday's law states that an electromotive force (electric field) is induced by a time-varying magnetic flux.
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45.
Which of the following is not the unit of energy?
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Answer: B —
Joules/second
Joules/second is equivalent to Watts, which is the unit of power, not energy.
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46.
The rise time 't' of a signal applied to CRO and bandwidth 'B' of the CRO are related as
Show answer and explanation
Answer: A —
$t \times B = 0.35$
The standard empirical relationship between rise time and bandwidth in an oscilloscope is $t_r \times \text{BW} \approx 0.35$ .
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47.
An oscilloscope is used to measure the phase difference or the frequency relationship between two unknown signals, it is used in the
Show answer and explanation
Answer: D —
X-Y mode
X-Y mode (Lissajous figures) is used to measure phase and frequency relationships between two signals.
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48.
A triangular wave shape is obtained in a function generator
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Answer: B —
by integrating a square wave
Integrating a square wave produces a linear ramp/triangular wave.
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49.
In a digital multimeter resistance is measured by using
Show answer and explanation
Answer: C —
Constant current source
A digital multimeter passes a constant current through the unknown resistance and measures the resulting voltage drop.
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50.
The delay line in CRO is placed after
Show answer and explanation
Answer: B —
Vertical amplifier
A delay line is introduced in the vertical deflection channel to delay the input signal so that the sweep can be triggered properly before the signal reaches the plates.
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51.
The recommended configuration for soldering is
Show answer and explanation
Answer: C —
Lap joint
Lap joints provide greater mechanical strength and larger surface area for electrical and electronic soldering connections.
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52.
Addition of ________ increases the mechanical property of a tin-lead solder.
Show answer and explanation
Answer: A —
Antimony
Antimony is added to tin-lead solder to increase its tensile strength and mechanical properties.
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53.
The purpose of using flux in soldering is
Show answer and explanation
Answer: C —
Prevents oxides forming
Flux cleans metal surfaces by removing and preventing the formation of metal oxides during soldering.
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54.
Heat for soldering process is supplied by
Show answer and explanation
Answer: D —
Any of the above
Depending on the application, soldering heat can be provided by soldering irons, induction, resistance heating, etc.
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55.
Temperature range in soldering process is
Show answer and explanation
Answer: B —
180°C - 250°C
Soft soldering typically uses temperatures ranging between $180^\circ\text{C}$ and $250^\circ\text{C}$ .
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56.
Tropospheric scatter is used with frequency in the following range
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Answer: A —
UHF
Tropospheric scatter propagation predominantly utilizes UHF and SHF frequency bands.
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57.
The maximum power of single side band waves under distortionless condition is
Show answer and explanation
Answer: C —
$P_c / 4$
In a standard AM signal, each sideband contains $\frac{P_c}{4}$ power at maximum modulation index.
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58.
Wide band FM is the case where the modulation index is
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Answer: B —
much greater than unity
In wideband FM, the modulation index is significantly greater than 1 ( $\beta \gg 1$ ).
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59.
In a super heterodyne receiver the frequency of local oscillator is
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Answer: C —
higher than that of incoming signal
In superheterodyne receivers, the local oscillator frequency is typically maintained higher than the incoming RF signal frequency ( $f_{LO} = f_s + f_{IF}$ ).
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60.
In a line of sight system the receiving and transmitting antenna heights are 10m and 100m respectively above the surface of the earth. The range of the system will be approximately
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Answer: D —
52 km
Line of sight range $d \approx 4.12 \times (\sqrt{h_t} + \sqrt{h_r}) = 4.12 \times (\sqrt{100} + \sqrt{10}) = 4.12 \times (10 + 3.16) = 4.12 \times 13.16 \approx 54.2\text{ km}$ (closest option is 52 km).
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61.
QPSK system uses a phase shift of
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Answer: A —
$\pi / 2$
Quadrature Phase Shift Keying (QPSK) uses four phase states separated by $90^\circ$ ( $\pi/2$ radians).
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62.
FDM uses ________ to prevent modulated signal from overlapping.
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Answer: A —
Guard band
Guard bands are narrow frequency bands used in FDM to prevent adjacent channels/signals from overlapping and causing crosstalk.
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63.
A 500W carrier is amplitude modulated to a depth of 60%. What is the total power of the transmitted wave.
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Answer: D —
590W
Total power $P_t = P_c \left(1 + \frac{m^2}{2}\right) = 500 \times \left(1 + \frac{0.6^2}{2}\right) = 500 \times (1 + 0.18) = 500 \times 1.18 = 590\text{W}$ .
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64.
Which fiber is preferred for long distance communication
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Answer: B —
Step index single mode
Step index single-mode fiber has virtually no intermodal dispersion and is ideal for long-distance, high-bandwidth communications.
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65.
Optical Time Domain Reflectometer is used to measure
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Answer: C —
Losses in optical fibre communication
OTDR is used to characterize fiber optic cables, measure attenuation/losses, and locate faults.
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66.
Which of the following is the feature of mobile communication?
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Answer: D —
All of the above
Modern mobile communication systems exhibit high scalability, load balancing, and robust network management.
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67.
The process of converting the analog sample into discrete form is called
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Answer: B —
Quantization
Quantization maps continuous/analog sample values to a discrete set of predetermined amplitude levels.
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68.
If physical quantities like force, tension, or pressure are to be measured, then LVDT acts as a
Show answer and explanation
Answer: B —
Secondary transducer
LVDT converts mechanical displacement into electrical output. When measuring force or pressure, a primary transducer (like a diaphragm) converts force to displacement, making LVDT a secondary transducer.
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69.
Identify the incorrect statement 1. LVDT gives high output value so that there is no need for any amplifier circuit for the amplification process 2. LVDT is not sensitive to stray magnetic field
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Answer: B —
Only statement 2
Statement 2 is incorrect because LVDT is sensitive to stray magnetic fields (requiring magnetic shielding), and statement 1 is also somewhat flawed in practice since amplification is often required.
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70.
Which metal will have a large range of detection by inductive proximity sensor?
Show answer and explanation
Answer: C —
Iron
Ferrous metals like iron have the highest sensing range with standard inductive proximity sensors.
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71.
In semiconductor strain guage, when a tensile strain is applied,
Show answer and explanation
Answer: B —
Resistance increases in p-type material
P-type semiconductor strain gauges exhibit an increase in resistance under tensile strain (positive piezoresistive effect).
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72.
Thermocouple works on
Show answer and explanation
Answer: A —
Seebeck effect
Thermocouples operate on the Seebeck effect, where a temperature difference between two dissimilar metals produces a voltage.
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73.
The temperature of steam at around 540°C can be measured by
Show answer and explanation
Answer: C —
Thermocouple
Thermocouples (such as Type K) are commonly used for industrial temperature measurements up to and around $540^\circ\text{C}$ .
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74.
In a thermistor, change in resistance is measured using a
Show answer and explanation
Answer: A —
Wheatstone bridge
A Wheatstone bridge circuit is commonly employed to measure small resistance changes in thermistors accurately.
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75.
Capacitive transducers can be used for the measurement of liquid level. The principle of operation used to this case is
Show answer and explanation
Answer: B —
Change of dielectric strength
Liquid level measurement using a capacitive probe relies on the change in net dielectric constant/permittivity as the liquid fills the space between plates.
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76.
Inductive transducers are mainly used for the measurement of
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Answer: D —
Displacement
Inductive transducers are primarily designed for measuring linear or angular displacement.
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77.
Which device provides electrical isolation between input circuit and output circuit?
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Answer: D —
Opto coupler
An optocoupler (opto-isolator) uses a light-emitting diode and a phototransistor to provide complete electrical isolation between input and output circuits.
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78.
An OR gate is equivalent to two switches connected in __________.
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Answer: B —
Parallel
Two switches connected in parallel realize a logical OR function (if either switch A OR switch B is closed, current flows).
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79.
The carry output of a two-input half-adder can be realised by using a _______ logic gate.
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Answer: C —
AND
The carry output of a half adder is the logical AND of the two inputs ( $C = A \cdot B$ ).
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80.
The Gray code equivalent of a 4-bit binary number 1010 is ________.
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Answer: B —
1111
Binary 1010 converted to Gray code: MSB remains 1 $\rightarrow$ 1, next is $1 \oplus 0 = 1$ , next is $0 \oplus 1 = 1$ , last is $1 \oplus 0 = 1$ . Result is 1111.
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81.
The XNOR gate gives a high output when inputs are ________.
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Answer: C —
equal
An XNOR gate outputs high (1) when all inputs are equal (either both 0 or both 1).
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82.
Ripple counters are _________ counters
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Answer: B —
Asynchronous
Ripple counters are asynchronous counters where the clock pulse ripples through the flip-flops sequentially.
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83.
Decade counter counts up to _______ states.
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Answer: C —
10
A decade counter counts 10 distinct states (0 through 9).
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84.
According to De Morgan's theorem NAND gate is equivalent to ________ gate.
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Answer: C —
Bubbled OR
De Morgan's law states $\overline{A \cdot B} = \overline{A} + \overline{B}$ , which represents an OR gate with inverted inputs (bubbled OR).
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85.
The number of select lines required to design an 8×1 multiplexer.
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Answer: B —
3
The number of select lines $n$ for a multiplexer with $2^n$ inputs is given by $2^n = 8 \Rightarrow n = 3$ .
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86.
A flip flop can ________ one bit of information.
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Answer: A —
Store
A flip-flop is a sequential logic circuit capable of storing a single binary digit (1 bit).
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87.
A _______ shift register can convert serial to parallel data.
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Answer: B —
SIPO
Serial-In Parallel-Out (SIPO) shift register accepts serial data input and makes it available simultaneously at parallel outputs.
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88.
Which one is an Analog to Digital converter?
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Answer: C —
R-2R ladder type
R-2R ladder type is a Digital to Analog Converter (DAC). (Note: Option C was marked correct in official key, referring to resistor ladder networks often categorized in the same chapter, though R-2R itself is a DAC).
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89.
A decade counter requires ________.
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Answer: A —
4 flip flops
A decade counter requires at least 4 flip-flops to represent up to decimal 9 (binary 1001).
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90.
Three T flip flops are connected to form a counter, how many counting sequences it can count.
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Answer: D —
8
Three flip-flops can represent $2^3 = 8$ distinct states ( $000$ to $111$ ).
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91.
8086 Microprocessor is a _________ bit processor.
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Answer: B —
16
8086 is a 16-bit microprocessor with 16-bit registers and internal/external data buses.
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92.
8086 Microprocessor flag register has ________ flags.
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Answer: B —
9
The 8086 flag register contains 9 active flags (6 status flags and 3 control flags).
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93.
_______ flag is used for debugging in 8086.
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Answer: D —
TF
The Trap Flag (TF) is used for single-step debugging in the 8086 processor.
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94.
8086 can access upto _________ memory locations.
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Answer: A —
1 MB
With 20 address lines ( $2^{20}$ ), the 8086 can address $1\text{ MB}$ of memory.
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95.
MOV AX, [BX] is an example of a ________ mode of addressing.
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Answer: C —
Register Indirect Addressing
Using a register like BX enclosed in brackets to hold the memory address is Register Indirect Addressing.
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96.
8051 is a ________ bit Microcontroller.
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Answer: A —
8 bit
Intel 8051 is an 8-bit microcontroller family.
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97.
Pin number 40 of the 8051 microcontrollers is _________.
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Answer: B —
VCC
Pin 40 of the 40-pin DIP 8051 microcontroller is the supply voltage pin ( $V_{CC}$ ).
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98.
Microcontrollers have no ________ flag.
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Answer: D —
Zero
The 8051 PSW register contains Carry, Auxiliary Carry, Overflow, and Parity flags, but does not have a dedicated Zero flag in the same manner as standard microprocessors (though zero status is handled via accumulator checks).
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99.
The Serial data communication in 8051 is controlled by _________ registers.
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Answer: A —
SCON
SCON (Serial Control) register configures and controls serial data communication in the 8051.
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100.
8051 Microcontroller have _________ interrupt signals.
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Answer: D —
5
The standard 8051 microcontroller has 5 interrupt sources (two external, two timer, and one serial).
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Questions with answersProvisional keyINDUSTRIAL TRAININGSame post
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Industrial Training
Date of test
04/10/2018
QP code
49/2018/OL

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