EST flashcards

35 cards. Read the term and the definition here. The deck at the top of this page is optional.

Ohm's Law

Voltage equals current multiplied by resistance (V = I × R). Any two known values determine the third, and it applies to the whole circuit or any single element.

Power Formula

Electrical power equals voltage times current (P = V × I). Substituting Ohm's law gives P = I²R and P = V²/R for resistive loads.

Series Resistance

In a series circuit, total resistance is the sum of individual resistances. The same current flows through every component and the voltage divides among them.

Parallel Resistance

In a parallel circuit, the reciprocal of total resistance equals the sum of the reciprocals of each branch. Voltage is equal across all branches.

Kirchhoff's Voltage Law

The algebraic sum of all voltage rises and drops around any closed loop in a circuit equals zero. It follows directly from conservation of energy.

Capacitive Reactance

Opposition a capacitor offers to AC, given by Xc = 1/(2πfC). It decreases as frequency or capacitance increases, and is infinite at DC.

Inductive Reactance

Opposition an inductor offers to AC, given by Xl = 2πfL. It increases with frequency and inductance, and is zero at DC.

Diode Forward Drop

A forward-biased silicon diode drops roughly 0.6 to 0.7 volts; germanium drops about 0.3 volts. Reverse bias blocks current until breakdown.

Resistor Color Code

Color bands encode value: black 0 through white 9. The third band is the multiplier; gold indicates ±5 percent tolerance and silver ±10 percent.

Voltmeter Connection

A voltmeter is placed in parallel with the component being measured and should have very high input impedance so it draws negligible current from the circuit.

Ammeter Connection

An ammeter is inserted in series with the circuit so all current flows through it. It must have very low resistance to avoid altering the measurement.

Oscilloscope Function

An oscilloscope displays signal amplitude on the vertical axis against time on the horizontal axis, showing waveform shape, period, and peak voltage.

Probe Compensation

Scope probes are adjusted against the calibrator square wave. Correct compensation shows flat tops; rounded corners mean under-compensation and overshoot means over-compensation.

Time-Domain Reflectometer

A TDR sends a pulse down a cable and times the reflection. Distance to the fault equals propagation velocity times round-trip time divided by two.

True-RMS Meter

A true-RMS meter computes the effective heating value of any waveform. Averaging meters under-read distorted or pulsed AC signals and are accurate only for sine waves.

Continuity Testing

Continuity checks for a low-resistance path between two points. Power must be removed from the circuit or the meter will give a false reading.

Free-Space Wavelength

Wavelength in meters equals 300 divided by frequency in megahertz. A half-wave dipole is about half this length and a quarter-wave vertical about one quarter.

VSWR

Voltage standing wave ratio describes impedance match quality. A 1:1 ratio is perfect; 2:1 reflects about 11 percent of power and 3:1 about 25 percent.

Characteristic Impedance

The impedance a transmission line presents to a traveling wave, set by conductor geometry and dielectric. Common values are 50 ohms for radio and 75 ohms for video.

Carson's Rule

Approximates FM bandwidth as twice the sum of peak frequency deviation and the highest modulating frequency. Wider deviation increases occupied bandwidth.

Decibel Definition

A logarithmic ratio: 10 log(P2/P1) for power and 20 log(V2/V1) for voltage. Plus 3 dB doubles power; plus 10 dB multiplies it by ten.

Repeater Offset

A repeater receives on one frequency and simultaneously retransmits on another. The difference between them is the offset, and a duplexer isolates the two paths.

Single-Mode Fiber

Fiber with a core near 8 to 10 micrometers that supports one propagation mode. It carries signals over long distances with low loss at 1310 or 1550 nanometers.

Multimode Fiber

Fiber with a 50 or 62.5 micrometer core supporting many modes. It is used for shorter runs at 850 or 1300 nanometers because modal dispersion limits distance.

APC Connector

An angled physical contact fiber connector polished at an 8-degree angle, usually green. It reduces back reflection but must never be mated with a non-angled connector.

T568A and T568B

Two wiring pinouts for twisted-pair connectors that differ in the green and orange pairs. Both ends of a straight-through cable must use the same standard.

Horizontal Cable Limit

Copper horizontal cabling is limited to 100 meters total, typically 90 meters of permanent link plus 10 meters of patch cords, per TIA standards.

Half-Splitting Method

A troubleshooting technique that tests the midpoint of a signal or power path, then repeatedly halves the suspect section to locate the fault quickly.

Short Versus Open

A short circuit has near-zero resistance and causes excessive current and blown fuses. An open circuit has infinite resistance and stops current flow entirely.

Intermittent Fault Causes

Failures that appear and disappear are commonly caused by thermal drift, cold solder joints, loose connectors, or cables that flex and break internally.

ESD Protection

Electrostatic discharge can destroy or degrade semiconductors invisibly. Grounded wrist straps, grounded mats, and conductive bags prevent latent damage during repair.

Electrical Shock Threshold

Current through the body causes harm: about 10 milliamps can prevent letting go, and 100 milliamps across the chest can be fatal within seconds.

Lockout Tagout

A procedure that isolates and locks all energy sources before servicing. After de-energizing, absence of voltage is verified with a tested meter.

Class C Fire

A fire involving energized electrical equipment. Carbon dioxide or dry chemical extinguishers are used; water must never be applied until power is removed.

One-Hand Rule

When probing live circuits, keep one hand behind you or in a pocket so current cannot pass across the chest, and stand on an insulating surface.