Units: milli, micro, nano and picoSpec 1.5
Cells are far too small to measure in metres, so we use smaller units. Each unit below is 1000 times smaller than the one before it.
| Prefix | Symbol | Power of ten | Unit of length |
|---|---|---|---|
| milli | m | 10⁻³ | millimetre (mm) |
| micro | µ | 10⁻⁶ | micrometre (µm) |
| nano | n | 10⁻⁹ | nanometre (nm) |
| pico | p | 10⁻¹² | picometre (pm) |
To go to a smaller unit, multiply by 1000: mm to µm, µm to nm, nm to pm. To go to a larger unit, divide by 1000. So 1 mm = 1000 µm, 1 µm = 1000 nm and 1 nm = 1000 pm.
Higher tier
Standard form
Higher tier
Standard form writes a number as a number between 1 and 10 multiplied by a power of ten. For example, 0.000 045 m is 4.5 × 10⁻⁵ m, and 3 200 000 is 3.2 × 10⁶. A negative power means a small number. You must be able to do calculations with numbers written in standard form.
Higher tier
Calculating with standard form
A cell is 2.5 × 10⁻⁵ m long. It is viewed at a magnification of ×400. Calculate the length of the image in mm.
- image size = real size × magnification
- 2.5 × 10⁻⁵ × 400 = 1.0 × 10⁻² m
- 1.0 × 10⁻² m = 0.01 m
- 0.01 m × 1000 = 10 mm
Answer: 10 mm