ETA CETa flashcards

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

Ohm's Law

The voltage across a resistor equals current times resistance (V = I × R). Rearranged, I = V/R and R = V/I. It applies to resistive elements at constant temperature and underlies all DC circuit analysis.

Electrical Power Formula

Power equals voltage times current (P = V × I). Substituting Ohm's law gives P = I²R and P = V²/R. The unit is the watt; one watt is one joule of energy transferred per second.

Series Circuit

A single path in which the same current flows through every component. Resistances add directly (R_total = R1 + R2 + …), voltages divide in proportion to resistance, and one open stops all current.

Parallel Circuit

Components share the same voltage across common nodes while current divides among branches. Conductances add, so 1/R_total = 1/R1 + 1/R2 + …, making total resistance lower than the smallest branch resistance.

Kirchhoff's Current Law

The algebraic sum of currents entering and leaving any node is zero: total current in equals total current out. It expresses conservation of charge and holds for every instant in time.

Kirchhoff's Voltage Law

The algebraic sum of voltage drops and rises around any closed loop is zero. Energy gained from sources equals energy dissipated in loads, allowing loop equations to solve unknown voltages and currents.

Voltage Divider Rule

Unloaded output of two series resistors: V_out = V_in × R2/(R1 + R2). Loading the output with a comparable resistance lowers the actual output, so the formula holds only when the load draws negligible current.

Thevenin Equivalent

Any linear two-terminal network reduces to one voltage source V_th in series with one resistance R_th. V_th is the open-circuit voltage; R_th is measured with sources deactivated (voltage sources shorted, current sources opened).

Norton Equivalent

A linear network reduces to a current source I_N in parallel with resistance R_N. I_N is the short-circuit current and R_N equals R_th; converting between Thevenin and Norton uses V_th = I_N × R_N.

Maximum Power Transfer

A source delivers maximum power to a load when load resistance equals source internal resistance. At that point efficiency is only 50 percent, so it suits signal and RF work, not power distribution.

RMS Value

The effective value of an AC waveform: the DC value producing the same heating in a resistor. For a sine wave RMS = peak/√2 ≈ 0.707 × peak; average value of a full sine cycle is zero.

Peak-to-Peak Voltage

The difference between the most positive and most negative instantaneous values of a waveform. For a symmetric sine wave it is twice the peak value, so peak-to-peak = 2√2 × RMS ≈ 2.828 × RMS.

Silicon Diode Forward Drop

A forward-biased silicon junction drops about 0.6 to 0.7 volts before conducting appreciably. Germanium is about 0.3 volts; Schottky diodes about 0.2 to 0.4 volts; LED drops range roughly 1.2 to 3.3 volts.

Diode Rectifier Operation

A diode passes current in one direction only, converting AC to pulsating DC. Half-wave rectification uses one diode; full-wave bridge uses four, doubling ripple frequency and improving transformer utilization.

Zener Diode Regulation

A Zener operates reverse-biased in controlled breakdown, holding a nearly constant voltage. With a series current-limiting resistor it clamps the load voltage; it must never be forward-biased without a limiter.

NPN Transistor Conventions

In an NPN BJT, collector current flows into the collector and out of the emitter; the base-emitter junction is forward-biased at about 0.7 volts and the base-collector junction is reverse-biased for amplification.

Transistor Current Gain Beta

Beta (h_FE) is the DC ratio of collector current to base current: I_C = β × I_B, and I_E = I_B + I_C. Beta varies widely with device, temperature, and operating current, so designs avoid depending on its exact value.

Transistor Saturation Region

With base current high enough, the collector-emitter voltage falls to a small value (about 0.2 volts) and the device behaves as a closed switch. Further base current does not increase collector current.

MOSFET Threshold Voltage

The gate-source voltage at which an enhancement-mode MOSFET begins to conduct significant drain current. It is a voltage-controlled device with extremely high gate resistance, so gate charge and ESD protection matter.

Capacitor Charge Equation

Charge stored equals capacitance times voltage: Q = C × V. Current is I = C × dV/dt, so voltage across a capacitor cannot change instantaneously and a capacitor blocks steady direct current.

RC Time Constant

Tau equals R × C for a resistor-capacitor circuit. The capacitor charges to about 63 percent of final voltage in one tau, and the circuit is treated as settled after roughly five tau.

Capacitive Reactance

X_C = 1/(2πfC), the opposition a capacitor presents to AC. It falls as frequency or capacitance rises, so a capacitor passes high frequencies and blocks low ones, forming the basis of coupling and bypass.

Inductive Reactance

X_L = 2πfL, the opposition an inductor presents to AC. It rises with frequency and inductance, so an inductor passes DC and low frequencies while choking high frequencies; current through it cannot change instantly.

LC Resonance

A parallel or series inductor-capacitor pair resonates at f = 1/(2π√(LC)), where inductive and capacitive reactances cancel. At resonance impedance is maximum in parallel and minimum in series.

Capacitors in Parallel

Parallel capacitors add directly: C_total = C1 + C2 + …, because their plates share the same voltage and their stored charges sum. This is the opposite of the resistor rule for parallel connection.

Capacitors in Series

Series capacitors combine reciprocally: 1/C_total = 1/C1 + 1/C2 + …, so total capacitance is less than the smallest unit. Each shares the same charge, and voltage divides inversely with capacitance.

Inductors in Series

Series inductors add directly: L_total = L1 + L2 + …, when their magnetic fields do not couple. Coupled inductors require a mutual-inductance term, and the result depends on winding orientation and polarity.

Decibel Power Ratio

Gain in decibels equals 10 × log10(P_out/P_in) for power, or 20 × log10(V_out/V_in) for voltage on equal impedance. Doubling power is about 3 dB; tenfold power is 10 dB.

Impedance Magnitude

For series R, L, and C, impedance magnitude is Z = √(R² + (X_L − X_C)²). Impedance combines resistance and net reactance as a complex quantity, with phase angle arctan((X_L − X_C)/R).

Voltage Source Internal Resistance

A real source is modeled as an ideal voltage source in series with internal resistance. Terminal voltage falls as load current rises: V_terminal = V_open-circuit − I × R_internal; a stiff source has very low internal resistance.

LED Series Resistor Sizing

Choose R = (V_supply − V_LED)/I_LED, using the LED forward drop for its color or type. The resistor limits current because an LED has no meaningful internal current limit and will overheat otherwise.

Ohmmeter Measurement Rule

Resistance is measured with the component de-energized, otherwise the meter reads circuit voltages and may be damaged. In-circuit readings are valid only when parallel paths are absent or accounted for.