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AQA A Level Physics復習筆記1.1.2 Powers of Ten

Category: A-level課程, 教材筆記, 福利干貨 Date: 2022年7月4日下午5:36

Powers of Ten

Physical quantities can span a huge range of values
For example, the diameter of an atom is about 10–10?m (0.0000000001 m), whereas the width of a galaxy may be about 1021?m (1,000,000,000,000,000,000,000 m)
- This is a difference of 31 powers of ten
Powers of ten are numbers that can be achieved by multiplying 10 times itself
It is useful to know the prefixes for certain powers of ten

Powers of Ten Table

1.1.2-Powers-of-Ten-Table-

Examples

5 kN = 5 kilonewtons= 5 × 103?N (5000 N)
7 nC = 7 nanocoulombs = 7 × 10-9?C (0.000000007 C)

Exam Tip

You will often see very large or very small numbers categorised by powers of ten, so it is very important you become familiar with these as getting these prefixes wrong is a very common exam mistake!

Common Unit Conversions

J & eV

A common unit conversion in physics is between Joules (J) and?electronvolts (eV)
The electronvolt is derived from the equation work done (or energy transferred)?W?=?qV
- 1 eV = 1.6 × 10–19?C × 1 V = 1.6 × 10–19?J
To convert from J → eV, divide by 1.6 × 10–19
To convert from eV → J, multiply by 1.6 × 10–19

J & kW h

Another common unit conversion in physics is between Joules (J) and kilowatt-hours (kW h)
To convert between J and kW h, expand the derived units and re-collect terms as follows:
- 1 kW h = 3600 kW s (since 1 hour = 3600 s)
- 3600 kW s = 3 600 000 W s (since 1 kW = 1000 W)
- 3 600 000 W s = 3 600 000 J = 3.6 MJ (since power = energy / time or 1 W = 1 J s–1)
To convert from J → kW h, divide by 3.6 × 106
To convert from kW h → J, multiply by 3.6 × 106