BCS Written EEE (892) key terms

At any node of a circuit, the algebraic sum of currents entering equals the sum leaving, because charge cannot accumulate at a point. It underpins nodal analysis and current-balance equations.

Any linear two-terminal network can be replaced by one voltage source in series with one resistance, found from open-circuit voltage and short-circuit current. It simplifies load calculations and maximum power transfer problems.

A source delivers maximum power to a load when load resistance equals the source's internal (Thevenin) resistance. Efficiency at that point is only fifty percent for a resistive source.

In a linear network with several independent sources, the response in any branch equals the sum of responses computed with each source acting alone and the others deactivated. It fails for power and other nonlinear quantities.

A systematic circuit method that assigns node voltages relative to a reference node and writes Kirchhoff current law equations at each unknown node. It yields a solvable set of simultaneous linear equations.

A circuit technique that defines circulating loop currents in planar networks and applies Kirchhoff voltage law around each mesh. Solving the resulting equations gives all branch currents.

The frequency at which a circuit's inductive and capacitive reactances cancel, making impedance purely resistive. For a series RLC circuit it equals one over two pi root LC.

The cosine of the phase angle between sinusoidal voltage and current, equal to real power divided by apparent power. A low value means large reactive current and heavier line losses.

The root-mean-square induced voltage in a winding equals 4.44 times frequency, turns, core flux density and core area. It links winding design, applied voltage and operating flux.

Power dissipated by circulating currents induced in a magnetic core by alternating flux. It grows with the square of frequency and flux density and is reduced by thin, insulated laminations.

Energy lost per cycle as the core material is repeatedly magnetised, proportional to the area of the B-H loop and to frequency. It is minimised by using soft magnetic materials.

The fractional difference between synchronous speed and actual rotor speed of an induction motor, usually expressed as a percentage. Slip is zero at no load and rises with mechanical loading.

The rotational speed of the rotating magnetic field, equal to 120 times supply frequency divided by number of poles. An induction rotor always turns slightly slower than this value.

The curve relating induction motor torque to slip, showing a stable low-slip region and a breakdown maximum. It determines starting torque, operating point and overload capability.

The rise in secondary terminal voltage when full load is removed at a stated power factor, expressed as a fraction of rated voltage. It measures how well a transformer or generator holds its output.

A method of expressing voltages, currents, powers and impedances as fractions of chosen base values. It simplifies transformer banks and multi-voltage networks because ratios cancel across the system.

A steady-state power system calculation that determines bus voltage magnitudes and angles plus branch power flows for given generation and demand. It supports planning, voltage control and contingency screening.

Adding capacitors, reactors or power-electronic devices to supply or absorb reactive power locally, thereby correcting power factor and holding bus voltage within limits. It also frees transmission capacity.

The maximum short-circuit current or apparent power a network position can deliver during a fault. Switchgear and cable ratings must exceed it to ensure safe interruption.

A device that continuously measures currents and voltages and trips a circuit breaker when quantities exceed settings indicating a fault. It must be selective, fast, sensitive and reliable.

An instrument transformer that steps high line current down to a standard low value for metering and relaying, while isolating secondary equipment from the high-voltage circuit.

The fraction of each switching period during which a semiconductor switch conducts. Varying duty cycle controls the average output voltage of choppers and switch-mode converters.

A control technique that varies the on-time of switching devices at fixed frequency to synthesise a desired average voltage or current waveform, widely used in inverters and motor drives.

A DC-to-DC converter that steps voltage down by chopping the input and smoothing with an inductor and capacitor. Output approximately equals input times duty cycle in continuous conduction.

A power-electronic circuit that converts DC input into an AC output of controllable magnitude and frequency by switching devices in a defined sequence. It is central to variable-speed AC drives.

The ratio of a system's Laplace-transformed output to its input under zero initial conditions. Its poles and zeros reveal stability, damping and frequency response.

A pair of graphs showing a system's open-loop magnitude and phase against logarithmic frequency. Gain margin and phase margin read from it indicate relative stability.

An algebraic test that counts right-half-plane roots of a characteristic polynomial by examining sign changes in the first column of a constructed array, without solving for roots.

A feedback controller combining proportional action on present error, integral action on accumulated past error, and derivative action on error trend, tuned to balance speed, accuracy and damping.

A heavily doped diode designed to operate safely in reverse breakdown, holding an almost constant voltage. It serves as a simple shunt voltage reference and regulator.

A high-gain differential voltage amplifier used with external feedback to realise precise amplification, filtering, summation and comparison functions in analog circuits.

A grid layout of a truth table in Gray-code order that allows visual grouping of adjacent minterms to obtain a minimal sum-of-products Boolean expression by hand.

A mathematical system of binary variables and logic operations with identities such as absorption and De Morgan's laws, used to simplify and prove digital logic expressions.

A bistable sequential logic element that stores one bit and changes state on a clock edge or control input. Registers and counters are built from interconnected flip-flops.

A signal that suspends a processor's current program, runs a designated service routine, then resumes. It enables timely response to peripherals without wasteful polling.

A hardware counter that resets a microcontroller unless firmware periodically clears it. It recovers embedded systems that hang because of software faults or transient interference.

A band-limited signal must be sampled at more than twice its highest frequency component to allow exact reconstruction. Violating it causes aliasing, where high frequencies masquerade as low ones.

The error introduced when a continuous amplitude is rounded to the nearest discrete level in an analog-to-digital converter. It sets a floor on achievable signal-to-noise ratio.

Dividing one IP address block into smaller logical networks using a subnet mask, which separates the network prefix from the host portion and reduces broadcast traffic.

A seven-layer conceptual framework describing network functions from physical transmission up to application services. It helps engineers isolate faults and compare protocol stacks.

The time required for cumulative cash inflows from a project to equal its initial investment. It is simple to compute but ignores cash flows after the cutoff and the time value of money.

The sum of a project's future cash flows discounted to today at a chosen rate, minus the initial outlay. A positive value indicates the project adds value.

A situation where an engineer's personal, financial or family interest could improperly influence professional judgement. It must be disclosed promptly and the affected decision avoided or reassigned.

Obtaining voluntary agreement from affected parties after fully disclosing relevant risks, benefits and alternatives in understandable terms. It upholds autonomy before engineering interventions that affect others.