SI Units

Ohm

Definition

The SI unit of electrical resistance, defined as the resistance between two points when a potential difference of one volt drives a current of one ampere (1 Ω = 1 V/A).

Explanation

Named after Georg Simon Ohm, who formulated Ohm's law (V = IR). A standard LED circuit resistor is typically 220–470 Ω; a human body's resistance ranges from 1,000 Ω (wet skin) to 100,000 Ω (dry skin). Resistors in series add directly: two 100 Ω resistors in series equal 200 Ω.

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RELATED TERMS

Meter

The SI base unit of length, defined as the distance light travels in 1/299,792,458 of a second.

Kilogram

The SI base unit of mass, defined by the Planck constant.

Second

The SI base unit of time, defined by the cesium-133 atom.

Kelvin

The SI base unit of temperature, starting at absolute zero.

Ampere

The SI base unit of electric current.