EST key terms

The relationship stating that voltage equals current multiplied by resistance (V = I × R). Knowing any two of the three quantities lets you calculate the third in a DC circuit.

The electrical potential difference between two points, measured in volts. It is the force that pushes charge through a circuit and is measured across components in parallel.

The rate of flow of electric charge through a conductor, measured in amperes. Current is measured by placing the meter in series with the circuit path.

The opposition to current flow in a material, measured in ohms. Resistance converts electrical energy into heat and depends on material, length, and cross-sectional area.

The rate at which electrical energy is transferred or consumed, measured in watts. In DC circuits it equals voltage times current, and it also equals current squared times resistance.

A circuit in which components are connected end to end so the same current flows through each. Total resistance is the sum of individual resistances and voltage divides among loads.

A circuit in which components share the same two nodes so voltage is equal across each branch while current divides. Total resistance is always lower than the smallest branch resistance.

A component that stores energy in an electric field between two plates separated by a dielectric. It blocks direct current while passing alternating current, and its opposition falls as frequency rises.

A component that stores energy in a magnetic field around a coil. It passes direct current while opposing changes in current, and its opposition rises with frequency.

The total opposition a circuit presents to alternating current, combining resistance and reactance and measured in ohms. It varies with signal frequency because reactance depends on frequency.

A two-terminal semiconductor that allows current to flow mainly in one direction. It is used for rectification, reverse-polarity protection, and signal detection in electronic circuits.

A three-terminal semiconductor device used to amplify signals or act as an electronic switch. Small base or gate signals control a much larger current between the other terminals.

A circuit, often built from diodes, that converts alternating current into pulsating direct current. Filtering and regulation stages usually follow to smooth the output.

A circuit or unit that delivers regulated DC voltage and current to equipment from a source such as mains or a battery. It typically includes transformation, rectification, filtering, and regulation.

The small residual AC variation superimposed on a DC output after rectification and filtering. Excessive ripple indicates failing filter capacitors or an overloaded supply.

A handheld instrument that measures voltage, current, resistance, and often continuity or other functions. Correct lead placement and the proper function setting are essential to avoid damage or injury.

A test instrument that displays a signal's voltage waveform over time on a screen. It reveals amplitude, frequency, shape, and timing details that a multimeter cannot show.

A test that confirms a low-resistance path exists between two points, usually signaled by a beep. It is used to verify conductors, fuses, and connections without power applied.

A meter that measures current by sensing the magnetic field around a conductor clamped in its jaws, without breaking the circuit. It is useful for measuring large load currents safely.

A test instrument that sends a pulse down a cable and analyzes reflections to locate faults, breaks, or impedance mismatches. The distance to a fault is calculated from the reflection delay.

An instrument that injects light pulses into a fiber and measures backscattered and reflected light to locate breaks, splices, and loss along the link. It reports distance and loss versus position.

A calibrated instrument that measures the optical power level arriving on a fiber, usually in dBm. It is used with a light source to verify link loss and transmitter output.

The number of complete cycles of a periodic signal per second, measured in hertz. Frequency determines wavelength and the behavior of reactive components in a circuit.

The physical distance between corresponding points of successive cycles of a wave, commonly expressed in meters or nanometers. In fiber optics it identifies the transmission window used, such as 1310 or 1550 nanometers.

A logarithmic unit used to express ratios of power or voltage, allowing very large ranges to be compressed into manageable numbers. Gains and losses in RF and optical links are commonly stated in decibels.

The process of varying a carrier signal's amplitude, frequency, or phase to carry information. It shifts baseband information to a frequency band suitable for transmission.

A steady high-frequency wave that is altered by modulation to convey information. The receiver tunes to the carrier frequency and recovers the original information from it.

The range of frequencies a system can carry or a signal occupies, measured in hertz. Wider bandwidth supports more information capacity but requires more spectrum.

The increase in signal power or amplitude provided by an amplifier or antenna system, often expressed in decibels. Gain offsets losses elsewhere in a link but cannot improve signal-to-noise ratio by itself.

The reduction in signal strength as it travels through a medium or component, usually expressed in decibels. It increases with distance and frequency in copper and optical links.

A thin glass or plastic strand that guides light along its core by total internal reflection. It carries high-bandwidth signals over long distances with immunity to electrical interference.

The decrease in signal power caused by inserting a component or cable into a link, measured in decibels. It is a key acceptance measure for connectors, splices, and installed links.

The small signal power lost at a joint where two fibers are permanently fused or mechanically joined. It is measured in decibels and contributes to the total link budget.

A tool that scores and breaks a fiber to produce a flat, perpendicular end face. A clean cleave is required before splicing or terminating to keep loss low.

A standardized classification of twisted-pair cable by supported frequency and data performance, such as Category 5e or Category 6. The rating guides which applications and distances the cable can support.

Unwanted signal coupling from one conductor or pair into another nearby pair. It degrades data signals and is reduced by proper twisting, spacing, and termination practices.

Connecting equipment and systems to earth or a common reference to provide a safe path for fault current. Proper grounding protects people and reduces electrical noise and interference.

The intentional joining of metal parts to form an electrically continuous path. Bonding ensures fault current can return to the source and keeps equipment at a common potential.

A safety procedure that isolates energy sources and applies locks and warning tags before work begins. It prevents accidental energization or release of stored energy during maintenance.

Specialized clothing and gear such as gloves, eye protection, and arc-rated clothing worn to reduce injury risk. Selection depends on the hazards identified for the task.

A systematic process of isolating a fault by gathering symptoms, forming hypotheses, and testing from the most likely or easiest point. It proceeds logically rather than by random part replacement.