Electricity
The terms, units, components and laws behind every circuit. 22 tools, all free and instant.
Terms
Voltage, current, resistance, power.
CurrentElectric current explained: what is actually moving, why conventional current runs opposite to the electrons, and what typical currents look like.Electric chargeWhat electric charge is, the size of the elementary charge, how coulombs relate to amp-hours, and why battery capacity is quoted in mAh.Electric powerElectrical power explained: the three forms of the power formula, real versus apparent power, and why your bill is in kilowatt-hours rather than kilowatts.Power factorPower factor explained without the hand-waving: what causes it, what a poor one costs you, typical values by load type, and how correction works.ResistanceHow resistance opposes current, what determines it in a conductor, how it changes with temperature, and how resistors combine in series and parallel.VoltageWhat voltage actually is, how it differs from current, the symbols and units used for it, and how to measure it safely with a multimeter.
Units
Amp, volt, watt, ohm, farad, decibel.
AmpereThe ampere explained: how it is defined, what one amp actually represents, the full prefix scale from picoamps up, and typical currents you will meet.DecibelThe decibel explained: why it is logarithmic, the difference between the power and amplitude formulas, and what dBm and dBW actually reference.FaradThe farad explained, why it is such an enormous unit that real parts are measured in microfarads, and the full capacitance scale with typical uses.Kilowatt-hourWhat a kilowatt-hour actually is, why your bill uses it instead of joules, and how much of it each appliance in the house gets through.OhmThe ohm defined, the standard resistor value series, why E12 values look so arbitrary, and the resistance scale from milliohms to gigaohms.VoltThe volt defined, what one volt means in energy terms, the prefix scale from microvolts to megavolts, and the voltages used around the world.WattThe watt explained: one joule per second, how it relates to volts and amps, the kilowatt-hour on your bill, and horsepower conversion.
Components
Resistors, capacitors, inductors.
CapacitorWhat a capacitor does, the main types and where each is used, how they combine in series and parallel, and the mistakes that make them fail.Capacitor codeTurn the three-digit code printed on a ceramic capacitor into picofarads, nanofarads and microfarads, with the tolerance letter decoded too.Circuit symbolsThe standard schematic symbols drawn as clean SVG — searchable, theme-aware, and downloadable or copyable as markup for your own diagrams.InductorHow an inductor stores energy in a magnetic field, why it resists changes in current, and where inductance is useful rather than a nuisance.Resistor colour codeDecode a resistor's colour bands into a resistance and tolerance, with a drawn resistor that updates as you pick each band, plus the full colour table.
Laws
Ohm, Kirchhoff, Coulomb.
Coulomb's lawThe force between two point charges: the formula, the constant, a worked example, and how it compares with gravity at the same distance.Kirchhoff's lawsKirchhoff's current and voltage laws explained with worked examples, the sign conventions that trip people up, and how to use them to solve a circuit.Ohm's lawOhm's law in all its rearranged forms, the power equations that come with it, worked examples, and the cases where the law does not actually hold.Voltage dividerHow two resistors split a voltage, the formula, why loading ruins the result, and the practical rule for choosing divider resistor values.