Units, prefixes and standard form

GCSE Physics, Required practicals, maths skills and the equations, 20 minutes

SI units, the prefixes from nano to giga, and standard form for very big and very small numbers.

What you will learn

Give the SI unit of each quantity
Convert prefixes such as kΩ, mA and nm
Write and calculate with numbers in standard form

SI units and prefixes

Every physics equation works when you put the numbers in SI units: metres, kilograms, seconds, amps, and the units built from them (newtons, joules, watts, volts, ohms).

A prefix in front of a unit is just a power of ten.

Prefix	Symbol	Multiply by
giga	G	10⁹
mega	M	10⁶
kilo	k	10³
milli	m	10⁻³
micro	μ	10⁻⁶
nano	n	10⁻⁹

A resistor is 4.7 kΩ. In ohms?
k means × 10³
4.7 × 10³ Ω = 4700 Ω

Going the other way you divide: 0.045 A is 0.045 ÷ 10⁻³ = 45 mA. If the number got bigger when the unit got bigger, you went the wrong way.

The rest of this lesson and its 9 practice questions are locked.

In this lesson

SI units and prefixes
Standard form
Try it: Standard form on the calculator
Try it: Your first conversion

9 practice questions, marked as you go; about 20 minutes in all.

In this unit: Required practicals, maths skills and the equations

The skills every physics paper tests: units and standard form, uncertainty and errors, planning, graphs, the equations and the required practicals side by side.

All of Required practicals, maths skills and the equations

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