THDC JE key terms

The maximum pressure a soil can carry at its base without failing in shear or settling beyond an acceptable limit. It governs the size of footings and is usually expressed in kN per square metre.

The resistance of a soil or material to sliding along an internal plane. In soil it comes from friction between grains plus cohesion, and it sets how steep a slope or how heavy a load can be supported.

The component of soil shear strength that does not depend on the applied normal stress. It is significant in clay and near zero in clean dry sand, and it is measured by triaxial or vane tests.

The numerical difference between a soil's liquid limit and plastic limit. It indicates how much moisture the soil can hold while remaining workable, and it is used to classify clays and silts.

Mechanical densification of soil by removing air voids, usually with rollers or vibrators at a controlled moisture content. It raises density and strength and reduces future settlement of fills and embankments.

The ratio of the strength or resisting capacity of a structure to the maximum load or stress expected on it. Values above one cover uncertainties in loads, material properties and analysis methods.

A design method that checks a structure against defined conditions of collapse and of serviceability rather than against a single allowable stress. Partial safety factors are applied separately to loads and to material strengths.

The internal turning effect at a section of a beam, equal to the sum of moments of all forces on one side of that section. It produces normal stresses that vary linearly across the depth.

The internal force acting across a section of a beam, equal to the algebraic sum of transverse forces on one side of the section. Its rate of change along the beam equals the applied load intensity.

The ratio of a cross-section's second moment of area to the distance from the neutral axis to the extreme fibre. Dividing the bending moment by it gives the maximum bending stress in the section.

A geometric property of an area describing how its material is distributed about an axis, equal to the sum of area elements times the square of their distances from that axis. It controls resistance to bending.

A field test of fresh concrete in which a standard cone is filled, lifted and the drop in height of the concrete is measured. It gives a quick indication of workability and consistency.

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

Keeping concrete moist and at a suitable temperature after placing so that cement hydration can continue. Adequate curing develops design strength and reduces surface cracking and permeability.

The process of determining the relative heights of points on the ground using a level instrument and staff readings. Differences of elevation are found from backsight and foresight readings, not from horizontal distance.

A fixed point of known or assumed elevation used as a reference for levelling and setting out works. Temporary benchmarks are established on site where permanent ones are not convenient.

A line on a map joining points of equal elevation. The spacing of contours shows ground steepness, and their shape reveals ridges, valleys and drainage patterns.

The cosine of the phase angle between voltage and current in an alternating-current circuit, equal to real power divided by apparent power. A low value means more current for the same useful power and higher losses.

The product of root-mean-square voltage and current in an AC circuit, measured in volt-amperes. It combines the real power that does work with the reactive power that oscillates in the circuit.

The portion of AC power that flows back and forth between source and reactive elements such as inductors and capacitors, measured in volt-amperes reactive. It does no net work but is needed to build magnetic and electric fields.

A static device that transfers electrical energy between two windings at the same frequency by mutual induction, changing voltage in proportion to the turns ratio. It works only on alternating current.

Power lost as heat when circulating currents are induced in the magnetic core of a machine by a changing flux. It is reduced by laminating the core and increases with the square of frequency and flux density.

Energy dissipated as heat each time the magnetic material of a core is magnetised through a cycle. It depends on the area of the material's hysteresis loop and on the frequency of reversal.

Deliberately connecting exposed metalwork or a circuit point to the general mass of earth through a low-resistance path. It limits touch voltage and gives fault current a return path so protection operates.

A switching device that opens a circuit automatically under fault conditions and can be reset and returned to service. Unlike a fuse, it interrupts current without being destroyed.

A sequence of processes that returns a working fluid to its initial state, allowing heat and work to be exchanged repeatedly. Examples include the Rankine and Otto cycles used in power and engine analysis.

A thermodynamic property equal to internal energy plus the product of pressure and volume. It is convenient for steady-flow devices because the heat added at constant pressure equals the change in enthalpy.

The ratio of useful work output to heat energy supplied in a power-producing cycle or engine. It is always less than one and is limited for a reversible cycle by the source and sink temperatures.

Stress is internal force per unit area within a material; strain is the resulting fractional change in length. Their ratio in the elastic range is the modulus of elasticity of the material.

How closely the reading of a measuring instrument agrees with the true value of the quantity. It is distinct from precision, which describes how repeatable the readings are with each other.

Comparing an instrument's indication with a reference standard and adjusting it so that readings fall within specified limits. It is performed over the working range and repeated at defined intervals.

A device that converts one form of energy into another, such as a thermocouple turning temperature into a small voltage. In measurement systems it is the element that senses the physical variable.

A relationship comparing two quantities of the same kind, and the statement that two such relationships are equal. Problems are solved by cross-multiplication or by expressing quantities as parts of a total.

A fraction expressed with denominator one hundred, used to compare quantities on a common scale. Percentage change is the difference divided by the original value, multiplied by one hundred.

The sum of a set of values divided by the number of values, also called the arithmetic mean. It is affected by extreme values, unlike the median.

Interest calculated on the original principal plus all interest already accumulated, so the amount grows geometrically. The amount after n periods is principal times one plus the rate raised to n.

A form of reasoning in which two or more given statements about categories lead to a conclusion that must follow. Validity depends on the logical form, not on whether the statements are factually true.

A reasoning item that asks for a pair of items related in the same way as a given pair. The relationship may be based on function, order, part and whole, or degree.

Finding the rule that generates a sequence of numbers, letters or figures and using it to supply the missing term. Common rules involve differences, ratios, squares or alternating patterns.

A puzzle in which words or numbers are transformed by a consistent rule and the candidate must apply or reverse that rule. Rules may shift letters, reverse order or substitute symbols.

Basic freedoms guaranteed to citizens by Part III of the Indian Constitution, enforceable through the courts. They include equality, freedom of speech, protection of life and personal liberty, and constitutional remedies.

Guidelines in Part IV of the Indian Constitution that the state should follow when making policy. They are not directly enforceable in court but are fundamental in governance.

A form of government in which the executive is drawn from and accountable to the legislature. India adopted it at the Union and state levels, with the Prime Minister or Chief Minister heading the council of ministers.

A seasonal reversal of prevailing winds that brings a wet and a dry season to a region. The Indian economy and agriculture depend heavily on the southwest monsoon rainfall between June and September.

Warming of a planet's surface because certain atmospheric gases absorb and re-emit outgoing infrared radiation. Human emissions of carbon dioxide and methane are intensifying the effect and changing the climate.

A region with an exceptionally high number of endemic species that has already lost most of its original vegetation. The Western Ghats and the eastern Himalaya are recognised hotspots in India.

The rule that a verb must match its subject in number and person. Singular subjects take singular verbs, and phrases between the subject and verb do not change the agreement.

Two ways of presenting the same action depending on whether the subject performs or receives it. The passive form uses a form of 'be' with the past participle and often omits the doer.

Reporting someone's words either exactly in quotation marks or by paraphrasing them in a subordinate clause. Indirect speech usually shifts tense, pronouns and time words back one step.

A fixed expression whose meaning cannot be worked out from the individual words, such as 'to bite the bullet'. Idioms are learned as whole units and often carry a figurative sense.

Volatile working memory in a computer that holds programs and data currently in use. Its contents are lost when power is removed, and its size strongly affects how many tasks can run smoothly.

Non-volatile memory whose stored contents are retained without power and are normally only read, not rewritten. It holds firmware such as the start-up instructions used when a computer is switched on.

System software that manages hardware resources, files and processes and provides services to application programs. Examples include Windows, Linux and Android.

Application software that arranges data in rows and columns of cells and recalculates formulas automatically when values change. It is widely used for budgeting, tabulation and simple data analysis.

A unique numerical label assigned to a device on a network so that data can be routed to and from it. IPv4 addresses are 32-bit, while IPv6 addresses are 128-bit.