BEL Probationary Engineer key terms

A linear two-terminal circuit can be replaced by a single voltage source in series with a single resistance, where the source equals the open-circuit voltage and the resistance is found with sources deactivated.

Any linear two-terminal network can be modelled as a current source in parallel with a resistance; the current is the short-circuit current and the resistance equals the open-circuit voltage divided by short-circuit current.

In a linear circuit with several independent sources, the response in any branch equals the algebraic sum of responses produced by each source acting alone while all others are set to zero.

A high-gain differential voltage amplifier with very high input impedance and low output impedance, used with feedback networks to build adders, integrators, filters and comparators.

Returning a fraction of the output signal to the input of an amplifier; negative feedback reduces gain but improves bandwidth, linearity and input/output impedance characteristics.

A pair of graphs showing a system's magnitude in decibels and phase in degrees against logarithmic frequency, used to judge gain margin and phase margin of a feedback system.

A stability test for closed-loop feedback systems that counts encirclements of the critical point minus one on the open-loop polar plot to determine closed-loop pole locations in the right half plane.

An algebraic method that builds an array from the coefficients of a characteristic polynomial to count right-half-plane roots, thereby deciding closed-loop stability without solving for poles.

A mathematical system of logic with variables taking values 0 and 1, governed by operations AND, OR and NOT, used to simplify and design digital logic circuits.

A grid layout of truth-table cells arranged in Gray code order so that adjacent cells differ in one variable, allowing manual minimisation of Boolean expressions into fewer logic gates.

A bistable digital storage element that holds one bit and changes state on a clock edge or control input; common types are SR, D, JK and T.

The minimum intervals before and after a clock edge during which a synchronous input must remain stable for a flip-flop to capture data reliably.

Stress is internal force per unit area within a material; strain is the resulting fractional deformation. Their ratio in the elastic region defines Young's modulus.

The slope of the linear elastic portion of a stress-strain curve, expressing a material's stiffness as stress divided by strain under uniaxial loading.

The negative ratio of lateral strain to longitudinal strain when a material is stretched; typical metals fall near 0.3, and the value approaches 0.5 for rubber.

A graph of the internal bending moment along a beam's length, whose slope equals shear force and whose maximum locates the most highly stressed cross-section.

A plot of internal transverse shear force along a structural member, changing slope where distributed loads act and jumping at concentrated loads or supports.

Effective length of a compression member divided by its least radius of gyration; larger values mean greater buckling susceptibility and lower allowable compressive stress.

The critical axial load at which a perfectly straight, pin-ended elastic column becomes unstable, equal to pi squared times flexural rigidity divided by effective length squared.

A measure of how an algorithm's running time grows with input size, usually written in big-O notation such as O(n log n) for efficient comparison sorting.

An asymptotic upper bound describing the growth rate of a function, used to compare algorithms by ignoring constants and lower-order terms as input size becomes large.

A technique where a function calls itself on smaller subproblems, requiring a base case to terminate and consuming stack space proportional to call depth.

Organising relational database tables to reduce redundancy and update anomalies by applying rules such as first, second and third normal form.

A column or minimal set of columns that uniquely identifies each row of a table and cannot contain null values; other tables reference it as a foreign key.

A scalar lambda for which a square matrix times a nonzero vector equals lambda times that vector; eigenvalues reveal system stability and natural frequencies.

A scalar computed from a square matrix that is nonzero exactly when the matrix is invertible and whose sign and magnitude relate to volume scaling and orientation.

An integral transform converting a time-domain function into the complex s-domain, turning linear differential equations into algebraic equations that are easier to solve.

A representation of a periodic function as a sum of sine and cosine terms at integer multiples of a fundamental frequency, widely used in signal and vibration analysis.

A rule assigning probabilities to the possible values of a random variable, described by a probability mass function for discrete cases or a density function for continuous cases.

A symmetric bell-shaped continuous distribution defined by its mean and standard deviation, in which about 68 percent of values lie within one standard deviation of the mean.

The mean is the arithmetic average of a data set; variance is the average squared deviation from that mean, and its square root gives the standard deviation.

A ratio compares two quantities of the same kind, while a proportion states that two ratios are equal; cross-multiplication solves for an unknown term.

A fraction expressed with denominator 100; percentage change equals the difference divided by the original value, multiplied by 100.

Distance equals speed multiplied by time; for fixed distance, speed and time are inversely related, and average speed is total distance divided by total time.

A deductive reasoning problem presenting two or more premises about categories, from which a conclusion must follow necessarily rather than merely plausibly.

A sequence of numbers following a hidden pattern such as constant difference, ratio, squares or alternating operations; the task is to identify the missing or wrong term.

The grammatical rule that a verb must match its subject in number and person, with care needed for collective nouns, indefinite pronouns and phrases between subject and verb.

Voice shows whether the subject performs the action (active) or receives it (passive); the passive uses a form of be plus the past participle.

Central bank actions such as changing the repo rate, cash reserve ratio or open market operations to influence money supply, inflation and credit in the economy.

The interest rate at which a central bank lends short-term funds to commercial banks against government securities, used as a key lever of monetary policy.