the resistance of a conductor is usually represented by the letter r. the unit of resistance is ohm (ohm), referred to as ohm. the symbol is ω (greek letter, transliterated into pinyin and pronounced as ōu mī ga), 1ω=1v/a. the larger units are kiloohms (kω) and megaohms (mω) (mega=million, that is, 1 million).

the basic unit of electric current is the ampere. 1 ampere is defined as: two infinitely long parallel straight wires 1 meter apart in a vacuum carry an equal constant current. when the force on each meter of wire is 2×10^- at 7n, the current in each conductor is 1 amp.

the main unit of voltage in the international system of units is volt (v), referred to as volt, represented by the symbol v. [1] 1 volt is equal to 1 joule of work done for every 1 coulomb of charge on the voltmeter, that is, 1 v = 1 j/c. the unit of strong voltage is usually kilovolt (kv), and the unit of weak voltage can be millivolt (mv) and microvolt (μv).