In physics we often need to express very large or very small quantities. SI prefixes help us do that quickly by attaching a small letter to a unit. Think of a prefix as a multiplier that tells you how many times bigger or smaller a unit is.
Imagine you have a ruler that can stretch or shrink. The prefix tells you how many times the ruler is stretched or shrunk. For example, kilo (k) means the unit is 1,000 times larger, while milli (m) means it’s 1/1,000 of the original size.
| Prefix | Symbol | Factor | Example |
|---|---|---|---|
| pico | p | \$10^{-12}\$ | 1 pF = \$1\times10^{-12}\$ F |
| nano | n | \$10^{-9}\$ | 1 nL = \$1\times10^{-9}\$ L |
| micro | μ | \$10^{-6}\$ | 1 μm = \$1\times10^{-6}\$ m |
| milli | m | \$10^{-3}\$ | 1 mL = \$1\times10^{-3}\$ L |
| centi | c | \$10^{-2}\$ | 1 cm = \$1\times10^{-2}\$ m |
| deci | d | \$10^{-1}\$ | 1 dm = \$1\times10^{-1}\$ m |
| kilo | k | \$10^{3}\$ | 1 km = \$1\times10^{3}\$ m |
| mega | M | \$10^{6}\$ | 1 MJ = \$1\times10^{6}\$ J |
| giga | G | \$10^{9}\$ | 1 GHz = \$1\times10^{9}\$ Hz |
| tera | T | \$10^{12}\$ | 1 Tb = \$1\times10^{12}\$ bits |
Tip 1: When converting between units, write the full unit with its prefix symbol. For example, 5 kJ is 5 × 103 J, not just 5 × 103 J.
Tip 2: Always check the exponent when you see a prefix. A common mistake is to mix up kilo (k) and mega (M). Remember: k = 103, M = 106.
Tip 3: Use the table as a quick reference during exams. It saves time and reduces errors.
Tip 4: Practice converting between prefixes in both directions. For instance, turn 2 mL into liters: 2 mL = 2 × 10-3 L = 0.002 L.
What is the value of 3 µs in seconds?