SSC JE Electrical key terms

The maximum pressure a soil can support without failing in shear or settling excessively. Shallow foundations are designed so the applied pressure stays safely below this value with a factor of safety.

A foundation whose depth is small relative to its width, usually transferring load to soil near the surface. Common types are isolated, combined, strip and raft footings used for light to moderate structural loads.

A large continuous slab covering the whole footprint of a structure and distributing load over a wide area. It suits weak soils or heavy loads where isolated footings would overlap or settle unevenly.

Unequal downward movement of different parts of a structure due to varying soil compressibility or load. It induces distortion, cracking and structural distress, so it is often more critical than total settlement.

A field test in which a split sampler is driven into the soil by a falling hammer, counting blows per depth increment. The resulting N-value gives an empirical index of soil density and strength.

The gradual volume reduction of saturated fine-grained soil as water is squeezed out under sustained load. It is time-dependent and governs long-term settlement of clay deposits beneath foundations and embankments.

The ratio of the volume of voids to the volume of solid particles in a soil mass. It indicates how loose or dense a soil is and links directly to compressibility and permeability.

The moisture content at which a fine-grained soil changes from plastic to liquid behaviour. It is determined by the Casagrande apparatus or cone penetrometer and is used to classify clays.

The numerical difference between the liquid limit and plastic limit of a soil. It measures the range of moisture content over which the soil remains plastic, indicating clay content and compressibility.

A simple workability test in which fresh concrete is placed in a standard cone, the cone removed, and the drop in height measured. It gives a quick indication of consistency for site control.

The mass of water divided by the mass of cement in a concrete mix. Lowering it increases strength and durability but reduces workability, so it is a central parameter in mix design.

A laboratory measure of concrete workability obtained by comparing the weight of concrete compacted by free fall with that fully compacted. Lower values indicate a drier, less workable mix.

Laboratory equipment used to test the soundness of cement by detecting expansion caused by unsound constituents such as free lime. Two indicator needles measure the change in distance after curing.

The internal turning effect at a section of a beam caused by external loads and reactions. It produces normal stresses varying linearly across the section and is central to beam design.

The internal force acting parallel to a cross-section of a structural member at a given point. Its variation along a beam is plotted as a shear force diagram used in design.

The ratio of a section's second moment of area to the distance from the neutral axis to its extreme fibre. It converts bending moment into maximum bending stress for design checks.

The distance between the centres of supports, or the clear span plus effective depth, whichever is smaller, used in design calculations. It determines the bending moment a beam or slab must resist.

Maintaining adequate moisture and temperature in freshly placed concrete so cement hydration continues. Proper curing develops strength and durability and prevents surface cracking and shrinkage.

The ratio of applied hydrostatic pressure to the resulting volumetric strain of a material. It measures resistance to uniform compression and relates to a fluid's compressibility.

The ratio of tensile or compressive stress to the corresponding strain within the elastic limit. It quantifies a material's stiffness and appears in deflection and buckling calculations.

The negative ratio of lateral strain to longitudinal strain when a material is stretched or compressed elastically. Typical metals lie near 0.3, and the value helps relate elastic constants.

It states that entropy of an isolated system never decreases and that heat cannot flow spontaneously from a colder to a hotter body. It sets the direction of real processes and limits cycle efficiency.

The maximum possible efficiency of a heat engine operating between two fixed temperatures, equal to one minus the sink temperature over the source temperature in kelvin. No real cycle can exceed it.

A thermodynamic property measuring the dispersal of energy and the irreversibility of a process. It increases in spontaneous processes and remains constant only in ideal reversible ones.

The ideal air-standard cycle for spark-ignition engines, comprising two isentropic and two constant-volume processes. Its efficiency depends mainly on the compression ratio and the specific heat ratio.

The ideal air-standard cycle for compression-ignition engines, with heat addition at constant pressure instead of constant volume. For the same compression ratio it is less efficient than the Otto cycle.

The ratio of the total cylinder volume to the clearance volume in a reciprocating engine. Higher values generally raise thermal efficiency but are limited by knock and mechanical stress.

A dimensionless ratio of inertial forces to viscous forces in fluid flow. It predicts whether flow is laminar or turbulent and is widely used in pipe and boundary-layer analysis.

An energy balance along a streamline for steady, incompressible, frictionless flow, relating pressure, velocity and elevation heads. It explains lift, venturi meters and flow through orifices.

A smooth, orderly flow in which fluid particles move in parallel layers with no mixing between them. It occurs at low Reynolds numbers and produces a parabolic velocity profile in pipes.

A graph plotting stress against strain for a material under load, showing the proportional, yield, ultimate and fracture points. It reveals elastic modulus, yield strength and ductility for design.

The relationship stating that current through a conductor is directly proportional to the potential difference across it and inversely proportional to resistance, at constant temperature. It underpins basic circuit analysis.

Two circuit rules: current into a node equals current out, and the algebraic sum of voltages around any closed loop is zero. They allow analysis of networks that simple series-parallel reduction cannot solve.

Any linear two-terminal network can be replaced by a single voltage source in series with a single resistance. This simplifies load calculations and fault-level estimates in power circuits.

Any linear two-terminal network can be replaced by a single current source in parallel with a single resistance. It is the dual of Thevenin's theorem and is useful for parallel-source problems.

The cosine of the phase angle between voltage and current in an AC circuit, equal to real power divided by apparent power. Low values increase current and losses for the same useful power.

The product of RMS voltage and RMS current in an AC circuit, measured in volt-amperes. It combines real and reactive power and determines the rating of transformers and generators.

An AC supply of three voltages equal in magnitude and 120 electrical degrees apart. It delivers constant power, uses less conductor material and drives efficient industrial motors.

A static device that transfers electrical energy between two circuits at different voltage levels through mutual induction. It changes voltage and current while keeping frequency and power essentially constant.

An AC motor in which the rotating magnetic field of the stator induces currents in the rotor, producing torque without electrical connection to the rotor. It is the workhorse of industry.

The difference between synchronous speed and actual rotor speed of an induction motor, usually expressed as a fraction of synchronous speed. It must be nonzero for torque to be produced.

Connecting exposed metal parts and the neutral point of a system to the general mass of earth through low-resistance paths. It limits touch voltage and clears faults safely.

A switch that automatically opens a circuit under abnormal current or fault conditions and can be reset. Unlike a fuse, it interrupts and re-establishes the circuit without replacement.