| tera | 1012 |
| giga | 109 |
| mega | 106 |
| kilo | 103 |
| deci | 10-1 |
| centi | 10-2 |
| milli | 10-3 |
| micro | 10-6 |
| nano | 10-9 |
| pico | 10-12 |
| femto | 10-15 |
A
prefix is placed in front of a unit to show that the unit is multiplied by a power of ten. It lets us write very large or very small values without long strings of zeros, for example 3 km instead of 3000 m, or 25 mA instead of 0.025 A.
Each prefix has a symbol: T (tera), G (giga), M (mega), k (kilo), d (deci), c (centi), m (milli), µ (micro), n (nano), p (pico) and f (femto). Take care with capital letters: M (mega, 10
6) and m (milli, 10
-3) are very different.
Converting to base units: replace the prefix by its power of ten.
4.7 kΩ = 4.7 × 103 Ω = 4700 ΩWorked example: green light has a wavelength of 550 nm. In metres:
550 nm = 550 × 10-9 m = 5.5 × 10-7 mSquared and cubed units: the power applies to the prefix too. Since 1 cm = 10
-2 m, 1 cm
2 = (10
-2 m)
2 = 10
-4 m
2.
Always convert prefixed values to base units before putting them into an equation, then give the final answer with a sensible prefix.