Current, Voltage, and Resistance
Electric current (I): The rate of flow of electrons through a conductor. Measured in amperes (A). 1 ampere = 1 coulomb of charge per second. Measured with an ammeter, wired in series with the circuit.
Voltage (V): The electrical potential difference between two points — the "pressure" that pushes electrons. Measured in volts (V). Also called electromotive force (EMF). Measured with a voltmeter, wired in parallel across the component.
Resistance (R): Opposition to current flow. Measured in ohms (Ω). Conductors have very low resistance; insulators have very high resistance.