Alternating Current
Noel M. Morris · 1985
As mentioned earlier, an alternating quantity is one which reverses its direction periodically, being in one direction (say the ‘positive’direction) at one moment and in the opposite direction (the ‘negative’ direction) the next moment. The frequency of alternations can be as low as once every few seconds or as high as once every few nanoseconds (1 ns = 10 − 9 s or 1 1 000 000 000 s) $$ (1\,{\text{ns = 1}}{{\text{0}}^{\text{ - }}}^9{\text{ s or }}\frac{1}{{1\,000\,000\,000}}\,{\text{s)}} $$ .