DRDO CEPTAM Tech-A key terms

A ratio compares two quantities of the same kind by division, while a proportion states that two ratios are equal. Unitary method and cross-multiplication solve most exam problems of this type.

A technique that first finds the value of one unit by division, then multiplies by the required number of units. It handles work, time, speed and cost problems quickly without formal algebra.

A fraction expressed with denominator 100, so 25% means 25 per hundred. Successive percentage changes multiply rather than add, which is the most common trap in aptitude questions.

Interest computed only on the original principal for the whole period, using the formula P x R x T divided by 100. It never earns interest on previously accrued interest.

Interest added to the principal at each period so that later interest is charged on a growing amount. The amount equals principal times one plus rate over 100 raised to the number of periods.

Problems where the rate of work is the reciprocal of the time taken, and combined rates add. If a person finishes a job in n days, one day's work is one over n.

An application of time and work in which inlet pipes add to the filling rate and outlet pipes subtract from it. Net rate is the algebraic sum of the individual rates.

The sum of all observations divided by their number. When every value increases or decreases by a fixed amount, the average changes by that same amount.

An average in which each value is multiplied by its weight before summing, then divided by the total weight. It is used for mixture and alligation problems.

A reasoning question giving two or more premises with statements like all, some or no, from which valid conclusions must be drawn. Venn diagrams are the standard solving tool.

A diagram using overlapping circles to show sets and their relationships. In reasoning tests it quickly reveals whether a conclusion necessarily follows from the given statements.

A question pair where the relationship between the first two items must be identified and applied to a third item to find its partner. Relationships include part-whole, cause-effect and category.

A set of items in which all but one share a common property; the candidate must identify the exception. The shared property may be numerical, alphabetical, or based on meaning.

Finding the next term of a sequence formed by a rule such as constant difference, squares, cubes, or alternating operations. Differences between consecutive terms often reveal the pattern.

A puzzle in which words or numbers are converted into a code by a fixed rule, and the candidate must apply or reverse that rule. Letter shifts and reversal are common patterns.

Reasoning problems describing family links in words or symbols, where the candidate must determine how two persons are related. Drawing a family tree avoids confusion over gender and generation.

Problems tracking a person's movement through turns such as left, right, north and south, asking for final direction or shortest distance. A sketch with fixed compass directions is the reliable method.

Puzzles placing people in a row or around a circle or square using clues about positions. Circular arrangements distinguish facing centre from facing outward, which reverses left and right.

The basic rights guaranteed to citizens by Part III of the Indian Constitution, including equality, freedom of speech, and protection of life. They are enforceable through writs in the courts.

Guidelines in Part IV of the Indian Constitution directing the state towards social and economic welfare. They are not enforceable in courts but are fundamental in governance.

The opening statement of the Indian Constitution declaring the source of authority as the people and listing objectives such as justice, liberty, equality and fraternity. It is used as an aid to interpretation.

Three laws stating that a body stays at rest or in uniform motion unless acted on by a net force, that force equals mass times acceleration, and that every action has an equal and opposite reaction.

The SI unit of force is the newton, the force that gives a one-kilogram mass an acceleration of one metre per second squared. In the CGS system the unit is the dyne.

Work is force multiplied by displacement in the direction of the force, measured in joules. Power is the rate of doing work, measured in watts, equal to one joule per second.

A measure of a body's resistance to change in its rotational motion, depending on mass and how it is distributed about the axis. It plays the role in rotation that mass plays in linear motion.

The process by which green plants use sunlight, carbon dioxide and water to make glucose and release oxygen, with chlorophyll as the pigment. It occurs mainly in the chloroplasts of leaf cells.

A specialised structure inside a cell performing a particular function, such as the nucleus, mitochondria, ribosome or chloroplast. Mitochondria release energy, while ribosomes build proteins.

The rule that a verb must match its subject in number and person, so a singular subject takes a singular verb. Phrases between subject and verb do not change the agreement.

Voice shows whether the subject performs the action or receives it. In the passive, the object becomes the subject and the verb becomes a form of be plus the past participle.

The correct choice among a, an and the. 'A' and 'an' are indefinite and depend on sound, while 'the' is definite and refers to a specific or already mentioned noun.

Selecting the correct preposition to express relations of time, place or direction, such as in, on, at, since and for. Fixed expressions and verbs with set prepositions must be memorised.

A group of words whose meaning cannot be understood from the individual words, such as 'to let the cat out of the bag'. Exams ask for the correct meaning or usage in a sentence.

The permissible upper and lower dimensions within which a manufactured part must lie. The difference between maximum and minimum limits is the tolerance, which controls fit and interchangeability.

The relationship between the sizes of a hole and shaft assembled together. Clearance fit always leaves a gap, interference fit always has the shaft larger, and transition fit may give either.

The intentional difference between the nominal sizes of a mating hole and shaft, set before tolerances are applied. It determines the type of fit and may be positive or negative.

A measuring instrument with a main scale and a sliding vernier scale that reads to fractions of a millimetre, commonly 0.02 mm. It measures outside, inside and depth dimensions.

A precision instrument using a calibrated screw and thimble to measure small dimensions, typically to 0.01 mm. The reading is the barrel scale plus the thimble division times least count.

The smallest measurement an instrument can read reliably. For a vernier it is one main scale division divided by the number of vernier divisions; for a micrometer it is the pitch divided by thimble divisions.

At constant temperature, the current through a conductor is directly proportional to the potential difference across it, giving V equals I times R. Resistance is the constant of proportionality.

In a series circuit the same current flows through all elements and resistances add. In a parallel circuit the voltage is common and the reciprocal resistances add to give the total conductance.

Two circuit laws: the current law states that currents entering a junction equal those leaving, and the voltage law states that voltages around any closed loop sum to zero. They solve complex networks.

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

A static device that transfers electrical energy between two coils by mutual induction, changing voltage level without changing frequency. It works on alternating current only, not on steady direct current.

Connecting exposed metal parts of equipment to the ground through a low-resistance path so fault current flows safely away. It protects people from electric shock and limits voltage rise.

Protective devices that interrupt a circuit when current exceeds a safe value. A fuse melts a wire element and must be replaced, while a circuit breaker trips and can be reset.

The standard arrangements of two members to be joined, namely butt, lap, tee, corner and edge joints. The joint type and plate thickness determine the edge preparation and weld pass sequence.

Imperfections such as porosity, slag inclusion, undercut, incomplete penetration and cracks. They weaken the joint and are detected by visual inspection, dye penetrant, magnetic particle or radiography.

A fusion process in which an electric arc between an electrode and the workpiece generates heat to melt and join metal. The electrode may be consumable, as in shielded metal arc welding.

A fusion process using a flame from burning a fuel gas with oxygen, most often oxy-acetylene. The flame has inner cone and outer envelope zones whose balance controls the weld.

Cutting speed is the relative speed between tool and workpiece surface, in metres per minute. Feed is the advance per revolution or per stroke, and depth of cut is the thickness removed in one pass.

Machining tasks performed on a lathe, including turning, facing, drilling, boring, threading and knurling. The workpiece rotates while a single-point tool is fed along or across it.

A standard notation listing a single-point tool's angles in fixed order, such as back rake, side rake, end relief and nose radius. It lets a tool be specified or ground to a known geometry.

Adding small amounts of impurity atoms to a pure semiconductor to increase its conductivity. Pentavalent doping gives n-type material with electrons, trivalent doping gives p-type with holes.

A two-terminal device formed by joining p-type and n-type semiconductor material. It conducts readily in forward bias and blocks current in reverse bias, so it acts as a rectifier.

A circuit that converts alternating current into direct current using diodes. Half-wave rectifiers use one diode, while full-wave and bridge types use two or four to use both half cycles.

A three-terminal semiconductor device with emitter, base and collector that can amplify or switch signals. In the common-emitter configuration it provides both current and voltage gain.

A high-gain differential amplifier available as an integrated circuit, used with feedback for amplification, filtering and arithmetic operations. Ideal characteristics include infinite input impedance and zero output impedance.

A device that converts one form of energy into another, such as a thermocouple converting temperature into voltage. In instrumentation it turns a measured quantity into an electrical signal.

A sensor whose electrical resistance changes when it is stretched or compressed with the surface it is bonded to. It measures mechanical strain and is widely used in load cells.

The difference between a measured value and the true value. Systematic errors are consistent and correctable by calibration, while random errors vary and are reduced by averaging repeated readings.