Quantities in the circuit

Current, voltage and resistance: what they mean, how you measure them and how Ohm's law links them. This is about direct current, as batteries supply it.

Current The current tells you how much electric current flows. You measure it with an ammeter, in amperes (A) and milliamperes (mA).
Voltage The voltage drives the current. You measure it with a voltmeter, in volts (V), in parallel with the part.
Resistance The resistance tells how strongly a part hinders the current. It is measured in ohms (Ω) and depends on the material, length and thickness.
Ohm's law Voltage, current and resistance are linked: R = U / I. With it you calculate a missing quantity.