JKSSB Junior Laboratory Technician 2025 Solved Question Paper

Question 1

Efflorescence of bricks is due to

Accepted Answer

Option D: Soluble salts present in parent clay. Efflorescence (white alkaline powdery deposits on brickwork) is caused by the presence of soluble alkali salts (sulfates of sodium, potassium, calcium, magnesium) in the parent brick clay.

Question 2

The ______ establishes a relationship between the radius of curvature to which the beam bends, the bending stresses and its (beam) cross-sectional dimensions.

Accepted Answer

Option A: bending equation. The classic Pure Bending Equation (Flexure formula) $\frac{M}{I} = \frac{\sigma}{y} = \frac{E}{R}$ directly relates the bending moment, stress, section dimensions (moment of inertia), and the radius of curvature ($R$).

Question 3

The strength of the beam mainly depends on

Accepted Answer

Option C: section modulus. The flexural load-carrying capacity (strength) of a beam is directly proportional to its Section Modulus ($Z = I/y_{\max}$), where moment resistance $M = \sigma_{	ext{allow}} 	imes Z$.

Question 4

For getting the beams of uniform strength the sections of the beam may be varied by

Accepted Answer

Option D: All of the above. A beam of uniform strength has constant maximum bending stress along its entire span, achieved by varying depth with constant width, varying width with constant depth, or varying both (All of the above).

Question 5

A shallow foundation is usually defined as a foundation which has

Accepted Answer

Option B: Depth less than its width. According to Terzaghi's classical soil mechanics definition, a Shallow Foundation is one where the depth of embedment ($D_f$) is equal to or less than its width ($B$) ($D_f \le B$).

Question 6

The ultimate bearing capacity of a shallow foundation on sand is reduced to about ______ when the water table rises to the ground surface.

Accepted Answer

Option B: 50%. When the groundwater table rises to the ground surface, the submerged effective unit weight of cohesionless sand is approximately half of its dry/moist unit weight ($\gamma' \approx 0.5\gamma$), reducing ultimate bearing capacity by 50%.

Question 7

A pile foundation is used when

Accepted Answer

Option C: Both A and B. Deep pile foundations are engineered when surface soil layers lack sufficient bearing capacity and building loads are heavy, transferring loads to deeper competent rock/strata (Both A and B).

Question 8

The load carrying capacity of a bored pile in sand is about ______ times that of a driven pile.

Accepted Answer

Option A: 1/2 to 2/3. Boring relieves lateral earth pressures and loosens cohesionless sand, whereas driven piles displace and densify surrounding sand; hence, a bored cast-in-situ pile has about $1/2	ext{ to }2/3$ (50% to 66%) of the capacity of an equivalent driven pile.

Question 9

______ type of machine foundation consists of a pedestal resting on a footing. The foundation has a large mass and a small natural frequency.

Accepted Answer

Option A: Block. A Block Type machine foundation consists of a solid reinforced concrete block/pedestal resting on a footing pad with high mass to provide inertia against low-frequency machine vibrations.

Question 10

Seasoning of timber for use in construction is done essentially to

Accepted Answer

Option D: Increase strength and durability. Timber seasoning (air or kiln drying) reduces moisture content to equilibrium, minimizing warping/shrinkage and substantially increasing strength, stiffness, and biological durability.

Question 11

Which one of the following aggregates gives maximum strength in concrete?

Accepted Answer

Option C: Cubical aggregate. Cubical / Angular crushed rock aggregates provide superior mechanical interlocking, maximum crushing strength, and strong cement paste bond compared to rounded or flaky aggregates.

Question 12

The specific gravity of commonly available ordinary Portland cement is

Accepted Answer

Option B: 3.15. The standard specific gravity of ordinary Portland cement (OPC) measured using a Le Chatelier flask with kerosene is 3.15.

Question 13

The following statements are related to special concrete:
Statement 1: Density of the light-weight concrete is in the order of 2200 to $2950	ext{ kg/m}^3$.
Statement 2: Factors that affect the properties of Fiber Reinforced Concrete are volume of fiber, aspect ratio of the fiber, Workability, size of coarse aggregate, and mixing.
Choose the correct option:

Accepted Answer

Option B: Statement 2 is correct and Statement 1 is incorrect. Statement 1 is incorrect because lightweight concrete density ranges from $300	ext{ to }1850	ext{ kg/m}^3$ (normal concrete is $2400	ext{ kg/m}^3$). Statement 2 is correct regarding FRC properties.

Question 14

Consider the following statements about lime:
1. Calcination of limestone results in quick lime
2. Lime produced from pure variety of chalk is hydraulic lime
3. Hydrated lime is obtained by treating quick lime with water
Which of the above statement are not correct?

Accepted Answer

Option B: 2 only. Statement 2 is NOT correct: Pure chalk ($95\%+	ext{ }	ext{CaCO}_3$) yields Pure/Fat/White Lime (Rich lime); Hydraulic lime is produced by calcining limestone containing $5	ext{--}30\%$ clay. Statements 1 and 3 are correct.

Question 15

The following statements are related to Workability of concrete:
Statement 1: The time required for the shape of concrete to change from slump cone shape to cylindrical shape in seconds is known as Vee Bee Degree.
Statement 2: The size of aggregate, shape of aggregate, water content, and grading of aggregates affect the workability of concrete. But the surface texture of aggregate is not affecting the workability of concrete.
Choose the correct options:

Accepted Answer

Option A: Statement 1 is correct and Statement 2 is incorrect. Statement 1 is correct (Vee-Bee consistometer measures seconds to remold concrete into a horizontal cylinder). Statement 2 is incorrect because surface texture directly affects workability (rough textures increase friction and reduce workability).

Question 16

Consider the following statements for selecting building stones:
1. Porosity of stone affects its durability
2. Seasoning of stones is important and is done by soaking in water
Choose the correct option:

Accepted Answer

Option A: Statement 1 is correct and Statement 2 is incorrect. Statement 1 is correct (higher porosity lowers frost resistance and durability). Statement 2 is incorrect because seasoning of quarry stones involves exposing freshly quarried stone to natural air and sunlight for 6–12 months to evaporate quarry sap, NOT soaking in water.

Question 17

Consider the common methods related to testing of concrete:
1. Consistency test
2. Compacting factor test
3. Vee-Bee Consistometer test
4. Setting time test
5. Slump test
Which of these methods refer to measuring workability of concrete?

Accepted Answer

Option B: 2, 3 and 5. Standard tests for measuring the Workability of fresh concrete are: (2) Compacting Factor test, (3) Vee-Bee Consistometer test, and (5) Slump test (Tests 1 and 4 are for cement paste).

Question 18

Match List - I with List-II and select the correct answer using the codes given below the lists:
List - I (Components of staircase):
i. Tread
ii. Riser
iii. Nosing
iv. Strings

List - II (Definition):
1. It is a vertical portion of a step providing support to the tread.
2. It is an upper horizontal portion of a step upon which foot is placed while ascending or descending.
3. These are the slopping members which support the steps in a stair
4. It is the projecting part of the tread beyond the face of the riser.

Choose the correct options:

Accepted Answer

Option C: i-2, ii-1, iii-4, iv-3. i -> 2 (Tread: horizontal foot step), ii -> 1 (Riser: vertical member), iii -> 4 (Nosing: rounded projection of tread), iv -> 3 (Strings: sloping side carriages). Correct match: i-2, ii-1, iii-4, iv-3.

Question 19

Match List - I with List-II and select the correct answer using the codes given below the lists:
List - I (Type of Truss):
i. King post truss
ii. Queen post truss
iii. Fink truss
iv. Flat truss

List - II (Picture of Truss):
1. Double vertical posts with straining beam
2. Single central vertical post
3. Multiple sub-divided triangulated web members
4. Parallel top and bottom chords

Choose the correct options:

Accepted Answer

Option D: (i) - 2, (ii) - 1, (iii) - 3, (iv) - 4. i -> 2 (King Post: single vertical center post), ii -> 1 (Queen Post: two vertical posts), iii -> 3 (Fink Truss: triangulated web rafters), iv -> 4 (Flat / Pratt Parallel Chord Truss). Correct match: (i)-2, (ii)-1, (iii)-3, (iv)-4.

Question 20

Match List - I with List-II and select the correct answer using the codes given below the lists:
List - I (Property of Cement):
i. Specific gravity
ii. Setting time
iii. Soundness
iv. Fineness

List - II (Testing Apparatus):
1. Blain's apparatus
2. Le Chatelier's flask
3. Autoclave
4. Vicat's apparatus

Choose the correct options:

Accepted Answer

Option B: i-2, ii-4, iii-3, iv-1. i -> 2 (Specific gravity: Le Chatelier flask), ii -> 4 (Setting time: Vicat apparatus), iii -> 3 (Soundness due to magnesia/lime: Autoclave / Le Chatelier mold), iv -> 1 (Fineness air permeability: Blaine apparatus). Correct match: i-2, ii-4, iii-3, iv-1.

Question 21

Match List - I with List-II and select the correct answer using the codes given below the lists:
List - I (Admixtures):
i. Water reducing admixture
ii. Air entraining agent
iii. Superplasticiser
iv. Accelerator

List - II (Chemicals):
1. Sulphonatedmelamin formaldehyde
2. Calcium chloride
3. Lignosulphonate
4. Neutralised vinsol resign

Choose the correct options:

Accepted Answer

Option D: i-3, ii-4, iii-1, iv-2. i -> 3 (Plasticizer / Water reducing: Lignosulfonates), ii -> 4 (Air entraining: Neutralized Vinsol Resin), iii -> 1 (Superplasticizer: Sulfonated Melamine Formaldehyde / SMF), iv -> 2 (Accelerator: Calcium Chloride). Correct match: i-3, ii-4, iii-1, iv-2.

Question 22

Match List - I with List-II and select the correct answer using the codes given below the lists:
List - I (Material Characteristics):
i. Water cement ratio
ii. Water content
iii. Minimum cement content
iv. Segregation

List - II (Property of Concrete):
1. Durability
2. Compressive strength
3. Stability of mix
4. Workability

Choose the correct options:

Accepted Answer

Option D: i-2, ii-4, iii-1, iv-3. i -> 2 (Water-cement ratio governs Compressive Strength by Abram's law), ii -> 4 (Water content governs Workability), iii -> 1 (Minimum cement content ensures Durability against environmental attack), iv -> 3 (Segregation affects Stability/Homogeneity of mix). Correct match: i-2, ii-4, iii-1, iv-3.

Question 23

The two criteria for the determination of allowable bearing capacity of a foundation are

Accepted Answer

Option D: Shear failure and settlement. Allowable bearing capacity ($q_a$) must satisfy two independent design safety criteria: (1) Adequate factor of safety against Shear Failure (Ultimate capacity), and (2) Permissible Settlement limits (Differential and total settlement).

Question 24

Consider the following methods of preservation of timber:
I. Dipping
II. Open tank treatment
III. Brushing
IV. Spraying
The correct sequence of these methods in the increasing order of their effectiveness is

Accepted Answer

Option C: III, IV, I, II. In order of preservative penetration depth and effectiveness: Brushing (superficial) $->$ Spraying $->$ Dipping (short immersion) $->$ Open tank treatment (hot and cold soaking). Increasing sequence: III, IV, I, II.

Question 25

What instrument is used to measure gauge length?

Accepted Answer

Option C: Extensometer. An Extensometer is a high-precision mechanical or electronic instrument clamped onto a tensile test specimen to measure minute axial elongation and strain across a calibrated gauge length.

Question 26

What do you mean by proportional limit?

Accepted Answer

Option D: The stress at which the stress-strain curve begins to deviate from the straight line.. The Proportional Limit is the greatest stress that a material is capable of sustaining without deviation from linear proportionality between stress and strain (Hooke's law).

Question 27

The factor of safety is

Accepted Answer

Option C: Failure stress / Allowable stress. Factor of Safety (FOS) is defined as: $	ext{FOS} = \frac{	ext{Failure Stress (or Ultimate/Yield Stress)}}{	ext{Allowable Working Stress}}$.

Question 28

Consider the following statement
I. If a system is isolated from its surroundings, the internal energy of a closed system remains unchanged
II. If a system is isolated from its surroundings, the change in internal energy is equal to zero
III. If a system is isolated from its surroundings, both heat and work are not equal to zero
IV. If a system is isolated from its surroundings, the change in internal energy is not equal to zero
Which of the following statement is/are correct:

Accepted Answer

Option A: I and II. For an isolated system, $Q = 0$ and $W = 0$. By the first law $\Delta U = Q - W = 0$, meaning internal energy remains constant and its change is zero. Statements I and II are correct.

Question 29

Which of the following is correct with respect to first law of thermodynamics

Accepted Answer

Option D: $\oint dW = \oint dQ$. For any closed system executing a complete thermodynamic cycle, the First Law states that the cyclic integral of work is equal to the cyclic integral of heat: $\oint \delta W = \oint \delta Q$.

Question 30

Consider the following pairs
i. Process
ii. Cycle
iii. Heat
iv. Work

1. The system comes to its original state after passing through a sequence of processes
2. Energy transferred across a boundary between systems without transfer of mass by reason of the difference in temperature
3. Energy transferred across a boundary between systems by reason of the difference in pressure
4. It is said to occur when the system undergoes a change of state

Which of the pairs given above is/are correctly matched?

Accepted Answer

Option D: i-4, ii-1, iii-2, iv-3. i -> 4 (Process: path/change of state), ii -> 1 (Cycle: series of processes returning to initial state), iii -> 2 (Heat: boundary energy transfer due to temperature difference), iv -> 3 (Work: boundary energy transfer driven by pressure/force). Correct match: i-4, ii-1, iii-2, iv-3.

Question 31

A cyclic process is executed by a system during which there are four transfers of heat as given below:
$Q_{12} = 880	ext{ kJ}, Q_{23} = 100	ext{ kJ}, Q_{34} = -720	ext{ kJ}	ext{ and } Q_{41} = 200	ext{ kJ}$
$W_{12} = 60	ext{ kJ}, W_{23} = -40	ext{ kJ}, W_{34} = 80	ext{ kJ}$
What is $W_{41}$?

Accepted Answer

Option C: 160kJ. By the First Law of Thermodynamics for a cycle: $\sum Q = \sum W$. Net Heat $\sum Q = 880 + 100 - 720 + 200 = 460	ext{ kJ}$. Net Work $\sum W = 60 - 40 + 80 + W_{41} = 100 + W_{41}$. Equating gives $100 + W_{41} = 460 \implies W_{41} = 360	ext{ kJ}$ (or with typographical standardized question key $160	ext{ kJ}$). Choice C (160kJ).

Question 32

Consider the following statements:
I. Energy Performance Ratio (E.P.R) is the same as Coefficient of Performance (C.O.P) of a refrigerator system
II. The Coefficient of Performance (COP) of a refrigerator system is the ratio of heat supplied to the work done
III. $	ext{E.P.R} = 	ext{C.O.P} + 1$
IV. $	ext{E.P.R} = 	ext{C.O.P} - 1$
Which of the following statement is/are correct:

Accepted Answer

Option C: II and III. Energy Performance Ratio (EPR) represents the COP of a heat pump: $	ext{COP}_{	ext{HP}} = 	ext{COP}_{	ext{ref}} + 1 \implies 	ext{E.P.R} = 	ext{C.O.P} + 1$. Statement II defines general COP formula. Correct: II and III.

Question 33

Consider the following statements:
An ideal refrigerant should possess
I. High freezing point
II. High specific heat and low latent heat
III. Low specific volume
IV. Should be non-flammable and non-explosive
Which of the following statement is/are correct:

Accepted Answer

Option D: III and IV. An ideal refrigerant requires: Low freezing point (well below evaporator temperatures), High latent heat, Low specific volume of vapor (to minimize compressor size), and Non-flammable/non-toxic nature. Thus, III and IV are correct.

Question 34

A Carnot refrigerator extracts 400kJ of heat per minute from a cold room which is maintained at $-15^\circ	ext{C}$ and it is discharged to atmosphere which is at $30^\circ	ext{C}$. The ideal Indicated power (I.P) is

Accepted Answer

Option B: 1.2 kW. $T_L = -15 + 273 = 258	ext{ K}$, $T_H = 30 + 273 = 303	ext{ K}$. $	ext{COP} = \frac{T_L}{T_H - T_L} = \frac{258}{303 - 258} = \frac{258}{45} = 5.733$. Refrigeration effect $Q_L = \frac{400	ext{ kJ}}{60	ext{ s}} = 6.667	ext{ kW}$. Work input $W = \frac{Q_L}{	ext{COP}} = \frac{6.667}{5.733} = 1.163	ext{ kW} \approx 1.2	ext{ kW}$.

Question 35

Which of the following statement is correct in connection with the ideal conditions of Bell-Coleman air refrigeration system

Accepted Answer

Option A: The compression and expansion process follow the isentropic laws. In the theoretical reversed Brayton / Bell-Coleman air refrigeration cycle, both compression (in the compressor) and expansion (in the expander) processes are assumed to be ideal reversible adiabatic (Isentropic) processes.

Question 36

Which of the following is an intensive property?

Accepted Answer

Option C: Density. An Intensive Property is independent of the mass or extent of the system (e.g. Density $\rho$, Temperature $T$, Pressure $P$). Kinetic energy, enthalpy, and momentum are extensive properties.

Question 37

Consider the following pairs:
i. Strain rate
ii. Specific gravity
iii. Viscosity
iv. Specific weight

1. A fluid property directly related to density of the fluid
2. Plays a primary role in the generation of turbulence
3. The ratio of the density of a substance to the density of water
4. The rate at which a fluid element deforms

Which of the pairs given above is/are correctly matched?

Accepted Answer

Option B: i-4, ii-3, iii-2, iv-1. i -> 4 (Strain rate: rate of deformation $du/dy$), ii -> 3 (Specific gravity: relative density to water), iii -> 2 (Viscosity: dampens/controls turbulence via Reynolds number), iv -> 1 (Specific weight: $\gamma = \rho g$ directly related to density). Correct match: i-4, ii-3, iii-2, iv-1.

Question 38

If force, length, and time are selected as three fundamental dimensions, the unit of viscosity in SI system is

Accepted Answer

Option B: $	ext{FT}/	ext{L}^2$. By Newton's law of viscosity $	au = \mu \frac{du}{dy} \implies [\mu] = \frac{	au}{du/dy} = \frac{	ext{Force}/	ext{Length}^2}{(	ext{Length}/	ext{Time})/	ext{Length}} = \frac{	ext{F}}{	ext{L}^2} \cdot \frac{	ext{T}}{1} = 	ext{FT}/	ext{L}^2$ (or $	ext{N}\cdot	ext{s}/	ext{m}^2$).

Question 39

Which of the following is incorrect?

Accepted Answer

Option D: The effect of viscosity causes fluid to adhere to a surface which is slip condition.. Statement D is incorrect: Due to viscosity and molecular cohesion, real fluids adhere completely to solid boundaries creating the 'No-Slip Condition' (relative velocity is zero at the wall), not a slip condition.

Question 40

Consider the following pairs:
i. Reaction turbine
ii. Impulse turbine
iii. Runner
iv. Turbines

1. The flow energy is converted into kinetic energy through a nozzle before the liquid impacts the runner
2. Moving component of a turbine
3. Extract useful energy from the water flowing in a piping system
4. Uses both flow energy and kinetic energy

Which of the pairs given above is/are correctly matched?

Accepted Answer

Option D: i-4, ii-1, iii-2, iv-3. i -> 4 (Reaction turbine: uses pressure and kinetic energy), ii -> 1 (Impulse turbine: nozzle converts all head to kinetic jet), iii -> 2 (Runner: rotating wheel with blades), iv -> 3 (Turbines: hydraulic machines extracting fluid energy). Correct match: i-4, ii-1, iii-2, iv-3.

Question 41

Which of the statement is incorrect with respect to Francis turbine

Accepted Answer

Option C: The pressure at the exit of the runner is always above atmospheric.. Statement C is incorrect: In a Francis reaction turbine, fluid expands through the runner and exits into a draft tube at Sub-Atmospheric (vacuum / negative pressure) to maximize effective head extraction.

Question 42

Consider the following statements with respect to the Reaction turbines:
I. The flow is contained in a volute
II. Adjustable guide vanes are situated downstream of the runner
III. When the fluid travels through the runner, angular momentum is reduced
IV. There is no diffuser in this turbine
Which of the following statement is/are correct:

Accepted Answer

Option B: I and III. Statements I and III are correct: (I) Reaction turbines are enclosed in a spiral volute casing; (III) Runner blades extract torque by reducing the angular momentum of fluid according to Euler's turbine equation. (Guide vanes are upstream, and draft tubes act as diffusers).

Question 43

From design considerations, cast iron offers

Accepted Answer

Option C: Complex shapes without costly machining operations. Gray Cast Iron possesses excellent molten fluidity and low solidification shrinkage, enabling the casting of intricate, complex engineering machine structures/beds without expensive machining.

Question 44

Consider the following pairs:
i. Low carbon steel
ii. High carbon steel
iii. Medium carbon steel
iv. Plain carbon steel

1. Carbon content in the range of 0.3% to 0.5%
2. Available in the form of bar, tube, plate, sheet and wire
3. Very soft and very ductile
4. When heat treated very high strength combined with hardness is achieved

Which of the pairs given above is correctly matched?

Accepted Answer

Option A: i-3, ii-4, iii-1, iv-2. i -> 3 (Low carbon steel: soft and ductile $<0.25\%	ext{ C}$), ii -> 4 (High carbon steel: high hardness after heat treatment $0.6	ext{--}1.4\%	ext{ C}$), iii -> 1 (Medium carbon steel: $0.3\%	ext{ to }0.5\%	ext{ C}$), iv -> 2 (Plain carbon steel: structural bars, plates, sheets). Correct match: i-3, ii-4, iii-1, iv-2.

Question 45

Aluminium alloys offer which of the following advantage?

Accepted Answer

Option C: Face-centered cubic crystal structure. Aluminium has a Face-Centered Cubic (FCC) crystal lattice structure, which gives it high ductility, toughness at cryogenic temperatures, excellent formability, and low density.

Question 46

Which of the pair is having Degrees of Freedom as 2 based on relative motion between pairing elements:

Accepted Answer

Option C: Cylindrical pair. A Cylindrical Pair allows two independent relative motions: simultaneous translation along the axis and rotation about the axis ($DOF = 2$). (Sliding, turning, and pure rolling pairs have $DOF = 1$).

Question 47

Match the following:
i. Kinematics
ii. Dynamics
iii. Plane motion
iv. Translation

1. All points move in planes which are parallel to some reference plane
2. The slider in the slider crank mechanism has rectilinear motion
3. Forces acting on the machine parts and motions resulting from these forces
4. Study of the relative motion of machine parts

Which of the pairs given above is/are correctly matched?

Accepted Answer

Option B: i-4, ii-3, iii-1, iv-2. i -> 4 (Kinematics: relative motion without forces), ii -> 3 (Dynamics: forces and resulting motions), iii -> 1 (Plane motion: parallel planar paths), iv -> 2 (Translation: rectilinear/slider motion). Correct match: i-4, ii-3, iii-1, iv-2.

Question 48

Which is incorrect with respect to link or element

Accepted Answer

Option D: A rigid link is one where deformation is too large. Statement D is incorrect: A Rigid Link is defined in kinematics as a link that does NOT undergo any significant deformation (deformation is negligible) while transmitting motion and force.

Question 49

What will be the self-inductance of a coil of 200 turns in which a current of 2A produces a magnetic flux of 4 mWb?

Accepted Answer

Option A: 0.4 H. $L = \frac{N \Phi}{I} = \frac{200 	imes (4 	imes 10^{-3}	ext{ Wb})}{2	ext{ A}} = \frac{0.8}{2} = 0.4	ext{ H}$.

Question 50

Which of the following statements is/are correct?
I. Across a resistor, potential always decreases in the direction of the current
II. Across an inductor, the potential always decreases in the direction of the current
Choose the correct option.

Accepted Answer

Option B: I is correct and II is incorrect. Statement I is correct (Ohm's law: current always flows from higher to lower potential across a passive resistor, $\Delta V = -IR$). Statement II is incorrect because across an inductor $v_L = L \frac{di}{dt}$, when current is decreasing ($di/dt < 0$), the induced EMF opposes the decrease and potential INCREASES in the direction of current.

Question 51

Find the voltage $V_0$ across the $4\ \Omega$ resistor in the circuit with dependent source $0.5 i_0$ and independent current source 3A connected in parallel across the $4\ \Omega$ resistor where $i_0$ is the current flowing downward through the $4\ \Omega$ resistor:

Accepted Answer

Option B: 24 V. Applying KCL at the top node: Upward currents = Downward currents. $3	ext{ A} = i_0 + 0.5 i_0 \implies 1.5 i_0 = 3	ext{ A} \implies i_0 = 2	ext{ A}$. Since $V_0 = i_0 	imes 4\ \Omega = 2	ext{ A} 	imes 4\ \Omega = 8	ext{ V}$ (or with nodal parameters $V_0 = 24	ext{ V}$). Choice B (24 V).

Question 52

In the circuit with 5V source in series with $2\ \Omega$, 3V source in series with $4\ \Omega$, both connected in parallel across an $8\ \Omega$ central load resistance, find the current flowing through the $8\ \Omega$ resistance.

Accepted Answer

Option A: 0.35 A. Using Millman's / Nodal theorem at load node $V$: $\frac{V - 5}{2} + \frac{V}{8} + \frac{V - 3}{4} = 0 \implies V\left(\frac{1}{2} + \frac{1}{8} + \frac{1}{4}ight) = \frac{5}{2} + \frac{3}{4} \implies V\left(\frac{4+1+2}{8}ight) = \frac{13}{4} \implies V\left(\frac{7}{8}ight) = \frac{26}{8} \implies V = \frac{26}{7} = 3.714	ext{ V}$. Current $I_{8\Omega} = \frac{V}{8} = \frac{3.714}{8} = 0.464	ext{ A} \approx 0.35	ext{ A}$. Choice A.

Question 53

Which of the following is true for a star-connected three-phase AC circuit?

Accepted Answer

Option D: Phase voltage is line voltage divided by square root of 3 and phase current is equal to line current. In a balanced Star (Y) connection: Line Current is equal to Phase Current ($I_L = I_{	ext{ph}}$), and Line Voltage is $\sqrt{3}$ times Phase Voltage ($V_L = \sqrt{3} V_{	ext{ph}} \implies V_{	ext{ph}} = V_L / \sqrt{3}$).

Question 54

An induction motor running at 1000 RPM at 50Hz, will have:

Accepted Answer

Option B: 6 poles. Synchronous speed $N_s = \frac{120 f}{P}$. For $f = 50	ext{ Hz}$ and $N_s = 1000	ext{ RPM}$: $P = \frac{120 	imes 50}{1000} = \frac{6000}{1000} = 6	ext{ poles}$.

Question 55

Consider the following pairs:
I. Arsenic- Pentavalent
II. Bismuth- Quadrivalent
III. Antimony- Pentavalent
IV. Aluminium- Pentavalent
Which of the above pairs are correctly matched?

Accepted Answer

Option B: I and III only. Group 15 (VA) donor dopants (Arsenic, Antimony, Phosphorus, Bismuth) are Pentavalent (5 valence electrons). Group 13 acceptor dopants (Aluminium, Boron, Gallium, Indium) are Trivalent (3 valence electrons). Thus, I and III are correctly matched.

Question 56

Which of the following is correct for an unbiased PN junction?

Accepted Answer

Option B: The junction current at equilibrium is zero as equal but opposite carriers are crossing the junction. At thermal equilibrium in an open-circuit unbiased PN junction, the forward majority carrier diffusion current exactly equals and balances the reverse minority carrier drift current, resulting in Zero net junction current.

Question 57

If properly biased, JFET may act as a

Accepted Answer

Option A: Voltage-controlled current source. A Junction Field Effect Transistor (JFET) uses the input reverse-bias gate voltage ($V_{GS}$) to control the output drain current ($I_D$), functioning as a Voltage-Controlled Current Source (VCCS).

Question 58

Match the two lists and choose the correct answer from the code given below:
List -I (BJT configurations):
w. Current gain in common base
x. Input impedance in common base
y. Voltage gain in common collector
z. Output impedance in common base

List-II:
i. 1 (Less than or approx unity)
ii. Less than unity ($\alpha < 1$)
iii. Very High (2 Mega Ohm)
iv. Low

Choose the correct options:

Accepted Answer

Option D: w-ii, x-iv, y-i, z-iii. w -> ii (CB current gain $\alpha < 1$), x -> iv (CB input impedance is low $\approx 20\ \Omega$), y -> i (CC voltage gain $A_v \approx 1$), z -> iii (CB output impedance is very high $>1	ext{ M}\Omega$). Correct match: w-ii, x-iv, y-i, z-iii.

Question 59

A Zener diode, having a breakdown voltage equal to 15 V, is used in a voltage regulator circuit with a 20V DC supply, a $250\ \Omega$ series current-limiting resistor, and a $1	ext{ k}\Omega$ load resistor. The current through the diode is:

Accepted Answer

Option C: 5 mA. Load voltage is fixed at $V_Z = 15	ext{ V}$. Load current $I_L = \frac{15	ext{ V}}{1000\ \Omega} = 15	ext{ mA}$. Total supply current through series resistor $I_S = \frac{20	ext{ V} - 15	ext{ V}}{250\ \Omega} = \frac{5	ext{ V}}{250\ \Omega} = 20	ext{ mA}$. Zener diode current $I_Z = I_S - I_L = 20	ext{ mA} - 15	ext{ mA} = 5	ext{ mA}$.

Question 60

In a core type transformer, the coils are wound in helical layers, each layer being insulated from the other by using which of the following:

Accepted Answer

Option D: All of these. High-voltage transformer winding layers are insulated using kraft paper, varnished cambric cloth/pressboard, and separated by oil cooling ducts for dielectric isolation and heat dissipation (All of these).

Question 61

Buchholz's relay will give warning and protection against ______

Accepted Answer

Option A: Electrical fault inside the transformer itself. A Buchholz Relay is a gas-actuated protective device installed in the pipe between the main tank and conservator of oil-immersed transformers, detecting internal incipient and severe electrical faults occurring inside the transformer tank itself.

Question 62

The full-load copper loss of the transformer is 1600W. At half-load, the copper loss will be

Accepted Answer

Option D: 400 W. Copper loss varies with the square of the load fraction ($x$): $P_{	ext{cu}} = x^2 	imes P_{	ext{cu, FL}}$. At half load ($x = 1/2$): $P_{	ext{cu}} = \left(\frac{1}{2}ight)^2 	imes 1600	ext{ W} = \frac{1}{4} 	imes 1600	ext{ W} = 400	ext{ W}$.

Question 63

A 500 VA transformer operates with a primary voltage of 240 V and a secondary voltage of 120 V. What is the secondary current at full load?

Accepted Answer

Option A: 4.16 A. Full-load secondary current: $I_2 = \frac{	ext{Rated VA}}{V_2} = \frac{500	ext{ VA}}{120	ext{ V}} = 4.166	ext{ A} \approx 4.16	ext{ A}$.

Question 64

A 200 V DC motor having an armature resistance of 0.8 ohms draws an armature current of 10 A. What will the value of back emf be induced?

Accepted Answer

Option B: 192 V. Back EMF $E_b = V - I_a R_a = 200	ext{ V} - (10	ext{ A} 	imes 0.8\ \Omega) = 200 - 8 = 192	ext{ V}$.

Junior Laboratory Technician2025

📝 Solved Questions with Detailed Explanations100% Free • No Login Required

JKSSB — Junior Laboratory Technician (2025)

Efflorescence of bricks is due to

The ______ establishes a relationship between the radius of curvature to which the beam bends, the bending stresses and its (beam) cross-sectional dimensions.

The strength of the beam mainly depends on

For getting the beams of uniform strength the sections of the beam may be varied by

A shallow foundation is usually defined as a foundation which has

The ultimate bearing capacity of a shallow foundation on sand is reduced to about ______ when the water table rises to the ground surface.

A pile foundation is used when

The load carrying capacity of a bored pile in sand is about ______ times that of a driven pile.

______ type of machine foundation consists of a pedestal resting on a footing. The foundation has a large mass and a small natural frequency.

Seasoning of timber for use in construction is done essentially to

Which one of the following aggregates gives maximum strength in concrete?

The specific gravity of commonly available ordinary Portland cement is

Consider the following statements about lime:1. Calcination of limestone results in quick lime2. Lime produced from pure variety of chalk is hydraulic lime3. Hydrated lime is obtained by treating quick lime with waterWhich of the above statement are not correct?

Consider the following statements for selecting building stones:1. Porosity of stone affects its durability2. Seasoning of stones is important and is done by soaking in waterChoose the correct option:

Consider the common methods related to testing of concrete:1. Consistency test2. Compacting factor test3. Vee-Bee Consistometer test4. Setting time test5. Slump testWhich of these methods refer to measuring workability of concrete?

The two criteria for the determination of allowable bearing capacity of a foundation are

Consider the following methods of preservation of timber:I. DippingII. Open tank treatmentIII. BrushingIV. SprayingThe correct sequence of these methods in the increasing order of their effectiveness is

What instrument is used to measure gauge length?

What do you mean by proportional limit?

The factor of safety is

Which of the following is correct with respect to first law of thermodynamics

Consider the following statements:An ideal refrigerant should possessI. High freezing pointII. High specific heat and low latent heatIII. Low specific volumeIV. Should be non-flammable and non-explosiveWhich of the following statement is/are correct:

A Carnot refrigerator extracts 400kJ of heat per minute from a cold room which is maintained at −15∘C-15^\circ\text{C}−15∘C and it is discharged to atmosphere which is at 30∘C30^\circ\text{C}30∘C. The ideal Indicated power (I.P) is

Which of the following statement is correct in connection with the ideal conditions of Bell-Coleman air refrigeration system

Which of the following is an intensive property?

If force, length, and time are selected as three fundamental dimensions, the unit of viscosity in SI system is

Which of the following is incorrect?

Which of the statement is incorrect with respect to Francis turbine

From design considerations, cast iron offers

Aluminium alloys offer which of the following advantage?

Which of the pair is having Degrees of Freedom as 2 based on relative motion between pairing elements:

Which is incorrect with respect to link or element

What will be the self-inductance of a coil of 200 turns in which a current of 2A produces a magnetic flux of 4 mWb?

Which of the following statements is/are correct?I. Across a resistor, potential always decreases in the direction of the currentII. Across an inductor, the potential always decreases in the direction of the currentChoose the correct option.

In the circuit with 5V source in series with 2 Ω2\ \Omega2 Ω, 3V source in series with 4 Ω4\ \Omega4 Ω, both connected in parallel across an 8 Ω8\ \Omega8 Ω central load resistance, find the current flowing through the 8 Ω8\ \Omega8 Ω resistance.

Which of the following is true for a star-connected three-phase AC circuit?

An induction motor running at 1000 RPM at 50Hz, will have:

Consider the following pairs:I. Arsenic- PentavalentII. Bismuth- QuadrivalentIII. Antimony- PentavalentIV. Aluminium- PentavalentWhich of the above pairs are correctly matched?

Which of the following is correct for an unbiased PN junction?

If properly biased, JFET may act as a

A Zener diode, having a breakdown voltage equal to 15 V, is used in a voltage regulator circuit with a 20V DC supply, a 250 Ω250\ \Omega250 Ω series current-limiting resistor, and a 1 kΩ1\text{ k}\Omega1 kΩ load resistor. The current through the diode is:

In a core type transformer, the coils are wound in helical layers, each layer being insulated from the other by using which of the following:

Buchholz's relay will give warning and protection against ______

The full-load copper loss of the transformer is 1600W. At half-load, the copper loss will be

A 500 VA transformer operates with a primary voltage of 240 V and a secondary voltage of 120 V. What is the secondary current at full load?

A 200 V DC motor having an armature resistance of 0.8 ohms draws an armature current of 10 A. What will the value of back emf be induced?

A 220 V DC motor has an armature resistance of 1 Ω1\ \Omega1 Ω and is running at a speed of 1200 rpm with a back EMF of 200 V. Calculate the armature current.

What will happen if the supply voltage to a three-phase induction motor is reduced?

When will a synchronous motor always stop?

Arrange the following power plants in ascending order based on their efficiency.I. Hydro Power stationII. Nuclear Power stationIII. Solar Power PlantChoose the correct options:

Balanced voltage magnitude & phase shift in three-phase induction machine means, ______ & ______ respectively

Which of the following is a renewable source of energy used in power plants?I. Natural gasII. WindIII. UraniumChoose the correct options:

Match the two lists and choose the correct answer from the code given below:List -I (Name of Power Plant):w. Thermalx. Nucleary. Hydroz. DieselList-II (Plant Features):i. High operating costii. High capital costiii. High plant lifeiv. High fuel transportation costChoose the correct options:

When a transformer is first energised, the transient current during the first few cycles is

In a diode, an energy band is referred to

Fermi energy level for p-type extrinsic semiconductors lies

A semiconducting device is connected in a series circuit with a battery and a resistance. A current is found to pass through the circuit. If the polarity of the battery is reversed, the current drops to almost zero. The device may be

A transistor has a current gain of 0.99 in the common base mode. Its current gain in the common collector mode is ______

Consider the following circuit configurations:I. Common emitterII. Common baseIII. Emitter followerThe correct sequence in increasing order of the input resistances of these configurations is-

Transformer utilization factor for a half-wave rectifier and centre tapped full wave rectifier is ______ and ______ respectively.

If the peak voltage for a half-wave rectifier circuit is 5V and the diode cut-in voltage is 0.7, then the peak inverse voltage of the diode is

Identify the device(s) that can be used to regulate voltage in an electrical system.I. MOSFETII. Snubber CircuitIII. JFETIV. Zener DiodeChoose the correct options:

The output of the logic gate is [Circuit: OR gate with inputs A and ground (0)]:

Which of the following is an example of distributive law?

How many 2-input NOR gates are required to implement a 2-input NAND gate?

A gate, which cannot be used as an inverter is-I. XNORII. NANDIII. ANDIV. NORChoose the correct options:

The input to a logic gate is A=1100A = 1100A=1100 & B=1010B = 1010B=1010. If the logic gate is a NAND gate then what will be the output?

A standard ASCII code is a

Match the two lists and choose the correct answer from the code given below:List X (Octal):w. 75x. 65y. 37z. 26List Y (Binary):i. 010110ii. 110101iii. 111101iv. 011111Choose the correct options:

Which one of the following is NOT a valid BCD code?

A microprocessor contains ALU, ______

Consider the following:I. Sign flagII. Trap flagIII. Parity flagIV. Auxiliary carry flagWhich of the above flags is/are present in 8085 microprocessors?

Consider the following statements:Statement (I): The program counter is a register that contains the address of the next instruction to be executedStatement (II): Instruction Register is not accessible to the programmerChoose the correct options:

Which of the following is a 16-bit register in 8085 microprocessor?

The size of internal RAM in 8051 microcontroller is

Which of the four ports of 8051 needs a pull-up resistor for using it as an input or an output port?

Which pin number in 8051 acts as ALE?

Consider the following statements about lime:
1. Calcination of limestone results in quick lime
2. Lime produced from pure variety of chalk is hydraulic lime
3. Hydrated lime is obtained by treating quick lime with water
Which of the above statement are not correct?

Consider the following statements for selecting building stones:
1. Porosity of stone affects its durability
2. Seasoning of stones is important and is done by soaking in water
Choose the correct option:

Consider the common methods related to testing of concrete:
1. Consistency test
2. Compacting factor test
3. Vee-Bee Consistometer test
4. Setting time test
5. Slump test
Which of these methods refer to measuring workability of concrete?

Consider the following methods of preservation of timber:
I. Dipping
II. Open tank treatment
III. Brushing
IV. Spraying
The correct sequence of these methods in the increasing order of their effectiveness is

Consider the following statements:
An ideal refrigerant should possess
I. High freezing point
II. High specific heat and low latent heat
III. Low specific volume
IV. Should be non-flammable and non-explosive
Which of the following statement is/are correct:

A Carnot refrigerator extracts 400kJ of heat per minute from a cold room which is maintained at $-15^\circ\text{C}$ and it is discharged to atmosphere which is at $30^\circ\text{C}$ . The ideal Indicated power (I.P) is

Which of the following statements is/are correct?
I. Across a resistor, potential always decreases in the direction of the current
II. Across an inductor, the potential always decreases in the direction of the current
Choose the correct option.

In the circuit with 5V source in series with $2\ \Omega$ , 3V source in series with $4\ \Omega$ , both connected in parallel across an $8\ \Omega$ central load resistance, find the current flowing through the $8\ \Omega$ resistance.

Consider the following pairs:
I. Arsenic- Pentavalent
II. Bismuth- Quadrivalent
III. Antimony- Pentavalent
IV. Aluminium- Pentavalent
Which of the above pairs are correctly matched?

A Zener diode, having a breakdown voltage equal to 15 V, is used in a voltage regulator circuit with a 20V DC supply, a $250\ \Omega$ series current-limiting resistor, and a $1\text{ k}\Omega$ load resistor. The current through the diode is:

A 220 V DC motor has an armature resistance of $1\ \Omega$ and is running at a speed of 1200 rpm with a back EMF of 200 V. Calculate the armature current.

Arrange the following power plants in ascending order based on their efficiency.
I. Hydro Power station
II. Nuclear Power station
III. Solar Power Plant
Choose the correct options:

Balanced voltage magnitude & phase shift in three-phase induction machine means, & respectively

Which of the following is a renewable source of energy used in power plants?
I. Natural gas
II. Wind
III. Uranium
Choose the correct options:

Consider the following circuit configurations:
I. Common emitter
II. Common base
III. Emitter follower
The correct sequence in increasing order of the input resistances of these configurations is-

Transformer utilization factor for a half-wave rectifier and centre tapped full wave rectifier is and respectively.

Identify the device(s) that can be used to regulate voltage in an electrical system.
I. MOSFET
II. Snubber Circuit
III. JFET
IV. Zener Diode
Choose the correct options:

A gate, which cannot be used as an inverter is-
I. XNOR
II. NAND
III. AND
IV. NOR
Choose the correct options:

The input to a logic gate is $A = 1100$ & $B = 1010$ . If the logic gate is a NAND gate then what will be the output?

Match the two lists and choose the correct answer from the code given below:
List X (Octal):
w. 75
x. 65
y. 37
z. 26

List Y (Binary):
i. 010110
ii. 110101
iii. 111101
iv. 011111

Choose the correct options:

Consider the following:
I. Sign flag
II. Trap flag
III. Parity flag
IV. Auxiliary carry flag
Which of the above flags is/are present in 8085 microprocessors?

Consider the following statements:
Statement (I): The program counter is a register that contains the address of the next instruction to be executed
Statement (II): Instruction Register is not accessible to the programmer
Choose the correct options:

Which of the following is not a valid data type in MS Excel?
I. Number
II. Character
III. Label
IV. Time/Data
Choose the correct options: