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Electrical Basics

Voltage, current, resistance, power and the laws that tie them together — explained for people who fix boards.

CurrentCurrent is the flow of electric charge through a conductor, measured in amperes (A). On a laptop board it shows how hard each rail and part is working.
Electrical PowerElectrical power is the rate at which energy is used or delivered, measured in watts (W): voltage times current. It decides heat, adapter size and battery life.
Floating InputA floating input is a logic input connected to nothing that defines its level. It picks up noise and reads high or low unpredictably, so boards use pull resistors.
Ground (GND)Ground is the common reference point of a circuit, defined as 0 V. Every voltage on a laptop board is measured against it, and every current returns through it.
Ohm's LawOhm's law links voltage, current and resistance: V = I × R. It explains voltage drops, short circuits and most quick calculations at the repair bench.
Open CircuitAn open circuit is a break in a current path, so no current can flow. On laptop boards it comes from blown fuses, cracked joints, corroded traces and lifted pins.
ResistanceResistance is how strongly a material or part opposes the flow of current, measured in ohms (Ω). It turns electrical energy into heat.
Short CircuitA short circuit is an unintended low-resistance path, usually from a rail to ground. On laptop boards it is the most common reason a rail collapses to 0 V.
VoltageVoltage is the difference in electrical potential between two points — the push that drives current through a circuit. It is measured in volts (V).
Voltage DividerA voltage divider is two resistors in series that produce a fraction of the input voltage at their junction. Laptop boards use them in feedback, enable and ID circuits.

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