Keentune

Electrical Science curriculum

8 chapters
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205 concepts
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free
Everything the adaptive question bank can teach and test in Electrical Science, from foundations through advanced practice. Work through it in order, or start practising and let the questions find your level.
A. Charge, current, voltage, and resistance
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The conserved property carried by electrons and protons.
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The unit of charge, and its relation to the elementary charge.
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Charge separation by contact and its discharge behavior.
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Force between charges falls with the square of distance.
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Force per unit charge, and field direction convention.
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Charge per unit time through a cross-section.
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One coulomb per second, and its modern definition.
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Positive-to-negative convention vs actual electron drift.
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Electrons move slowly even though signals propagate fast.
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Energy per unit charge between two points.
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Voltage is always measured BETWEEN two points.
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Source emf minus the drop across internal resistance.
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Why terminal voltage sags under load.
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Opposition to current, measured in ohms.
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Material property; resistance equals rho times length over area.
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The reciprocal of resistance, measured in siemens.
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Loosely bound valence electrons giving low resistivity.
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Tightly bound electrons and dielectric breakdown limits.
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Between conductor and insulator, controllable by doping.
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Metal resistance rises with temperature; semiconductors fall.
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Zero resistance below a critical temperature.
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Reading value and tolerance from the band sequence.
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Rated value vs the guaranteed band and thermal limits.
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Infinite resistance vs near-zero, and the current each produces.
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Standard symbols for source, resistor, capacitor, inductor, switch.
B. Ohm's law, power, and energy
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Voltage equals current times resistance.
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Current equals voltage over resistance.
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Resistance equals voltage over current.
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Devices whose resistance is constant vs those that are not.
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The slope of the current-voltage curve as conductance.
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Power equals voltage times current.
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Power equals current squared times resistance.
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Power equals voltage squared over resistance.
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Pick the formula whose two known quantities you already have.
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Doubling current quadruples dissipation, not doubles it.
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One joule per second, the unit of power.
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Energy in joules or watt-hours.
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The billing unit, and converting from watts and hours.
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Kilowatt-hours times rate, to the exact cent.
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Charge delivered equals current times duration.
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Amp-hours and what they do and do not tell you.
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Useful output power over input power.
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Resistive dissipation as the origin of conductor heating.
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Why a resistor's wattage rating is a thermal limit.
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Maximum load power when load matches source resistance.
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Long runs and small conductors losing usable voltage.
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Raising voltage cuts current and cuts I-squared-R loss.
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Which element consumes and which supplies energy.
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Passive sign convention for power in a circuit element.
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Milli, kilo and mega applied consistently through a calculation.
C. Series, parallel, and network analysis
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One path; the same current through every element.
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Multiple paths; the same voltage across every branch.
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Total resistance is the sum of the parts.
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Reciprocal sum; for two, product over sum.
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Parallel total is always less than the smallest branch.
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N equal resistors in parallel give R over N.
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Collapsing a network stepwise to one equivalent.
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Current equals source voltage over total series resistance.
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Each branch current set by its own resistance.
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Output equals input times the ratio of resistances.
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Branch current in inverse proportion to branch resistance.
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Currents into a node equal currents out.
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Voltages around any closed loop sum to zero.
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Loop currents as the unknowns in simultaneous equations.
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Node voltages as the unknowns, using KCL.
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One source at a time, then sum the contributions.
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Any linear network as one source and one series resistance.
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The current-source dual of Thevenin.
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Converting between the two equivalents.
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Null-balance measurement and the balance condition.
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A chosen zero-potential node, not necessarily earth.
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Adding series loads reduces current and dims all of them.
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Parallel loads keep full voltage and draw independent current.
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One break stops all current in a series string.
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One open branch leaves the others operating.
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A short bypasses its branch and raises total current.
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Capacitance adds directly.
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Reciprocal sum; the opposite rule to resistors.
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The classic error: applying the wrong combination rule.
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Inductors combine like resistors, not like capacitors.
D. Magnetism and electromagnetic induction
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Field lines, poles, and the closed-loop property.
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Circular field around current, with the right-hand rule.
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Coiling concentrates the field and creates poles.
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Current-controlled magnetism and the effect of a core.
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How readily a material carries magnetic flux.
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Domain alignment producing strong, retainable magnetization.
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Lagging magnetization and the energy lost per cycle.
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Field times area, measured in webers.
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Flux per unit area, measured in teslas.
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Induced emf is proportional to the rate of change of flux.
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Induced current opposes the change that produced it.
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A conductor moving through a field generating voltage.
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Rotating a coil in a field producing alternating emf.
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Force on a current-carrying conductor in a field.
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A spinning motor generating opposing voltage and limiting current.
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Why a stalled or starting motor draws far more current.
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A coil opposing changes in its own current.
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The unit of inductance, defined by volts per amp per second.
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Collapsing field producing a high-voltage spike.
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Providing a path for inductive current to protect switches.
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Flux from one coil linking another.
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Alternating flux coupling primary to secondary.
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Voltage ratio equals turns ratio; current ratio is inverse.
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Copper, core, eddy-current and hysteresis losses.
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An electromagnet mechanically switching a separate circuit.
E. Alternating current fundamentals
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Periodically reversing polarity vs one-directional flow.
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Amplitude, frequency, period and phase.
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One is the reciprocal of the other.
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Two pi times frequency, in radians per second.
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The maximum instantaneous value of the waveform.
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Twice the peak for a symmetric waveform.
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Zero over a full cycle for a pure sinusoid.
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The DC value producing the same heating effect.
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Peak divided by the square root of two.
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Nameplate and mains voltages are RMS, not peak.
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Angular displacement between two waveforms.
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Which waveform reaches its peak first.
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Rotating vectors replacing time-domain trigonometry.
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Rectangular and polar forms for impedance arithmetic.
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Sine, square, triangle and sawtooth, and their harmonic content.
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Integer multiples of the fundamental distorting the wave.
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Peak over RMS, and why it matters for equipment ratings.
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One alternating source and its return.
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Three sources 120 degrees apart, and why it is used for power.
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The two three-phase connections and their voltage relations.
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Root-three relations between line and phase values.
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Instantaneous power varying through the cycle.
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Watts: the component that does useful work.
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Volt-amps reactive: energy shuttled and returned.
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Volt-amps: the product of RMS voltage and RMS current.
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The right-triangle relation among the three powers.
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Real over apparent power, equal to the cosine of the phase angle.
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Adding capacitance to offset inductive lag.
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Converting AC to pulsating DC with diodes.
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Capacitor filtering and the residual variation.
F. Reactance, impedance, and time constants
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Stores charge; opposes changes in voltage.
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Charge stored per volt applied, in farads.
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One half C V squared stored in the field.
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Insulating material raising capacitance and setting voltage rating.
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Falls as frequency rises; blocks DC, passes AC.
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Stores energy in a field; opposes changes in current.
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One half L I squared stored in the field.
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Rises as frequency rises; passes DC, blocks AC.
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Reactance stores and returns; resistance dissipates.
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The complex sum of resistance and net reactance.
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Root of resistance squared plus net reactance squared.
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Current leads voltage in a capacitive circuit.
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Current lags voltage in an inductive circuit.
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Reactances cancel; impedance is minimum and current maximum.
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Impedance is maximum and line current minimum.
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Set by the inductance-capacitance product.
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Sharpness of the resonance peak and stored-to-lost energy ratio.
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Resonant frequency over Q, between the half-power points.
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Low-pass, high-pass, band-pass and band-stop topologies.
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The half-power point where output falls to 0.707.
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Tau equals R times C, in seconds.
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About 63 percent in one time constant, 99 percent in five.
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Exponential decay with the same time constant.
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Tau equals L over R for current rise and decay.
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The settling response vs the eventual condition.
G. Semiconductors and components
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Adding impurities to create N-type and P-type material.
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The depletion region and its built-in potential.
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Conducting above the forward voltage drop.
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Blocking until reverse breakdown.
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About 0.7 V for silicon, 0.3 V for germanium.
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Deliberate reverse breakdown used for regulation.
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A junction that emits photons on recombination.
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One diode passing alternate half-cycles.
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Four diodes using both half-cycles.
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NPN and PNP three-layer devices.
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Saturation and cutoff as the two switching states.
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Small base current controlling a larger collector current.
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Beta as the collector-to-base current ratio.
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Voltage-controlled device with an insulated gate.
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Latching devices for AC power control.
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High-gain differential amplifier and its ideal assumptions.
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Trading gain for linearity and stability.
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Maintaining constant output against input and load change.
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Light-controlled semiconductor devices.
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Resistance varying strongly with temperature.
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Voltage-dependent resistance for surge suppression.
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Overcurrent protection by melting vs by tripping.
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Pole and throw notation, and momentary vs latching.
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Primary vs secondary cells and nominal cell voltages.
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Series adds voltage; parallel adds capacity.
H. Safety, grounding, and distribution
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Current through the body, not voltage alone, causes injury.
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Perception, let-go and fibrillation current ranges.
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Skin condition dominating the total path resistance.
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Hand-to-hand paths crossing the heart are the dangerous ones.
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Ionized-air fault energy as a thermal and blast hazard.
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Providing a fault path and a stable reference potential.
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Connecting metal parts together vs connecting to earth.
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The path that lets overcurrent protection operate.
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Comparing outgoing and returning current to detect leakage.
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Detecting the signature of an arcing fault.
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Sizing protection to the conductor, not to the load.
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A fault path vs sustained excess demand.
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Verified de-energization before work begins.
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Proving the tester, testing, then proving the tester again.
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Rated gloves, tools and clothing for the task voltage.
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The chain from generation through transmission to service.
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Transformers raising voltage for transport and lowering it for use.
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Typical transmission, distribution and service levels.
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Two hot legs and a neutral from a center-tapped transformer.
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Sags, swells, harmonics and transients and their effects on load.
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