Units, prefixes and scientific notation
It is important to know and be able to recall the prefixes that are used with units. May students lose marks in their assessments because they miss unit prefixes in their calculations. An example is when time is given in ms, which stands for milli seconds or 1 x 10-3 s. Some students mistakenly think metre seconds. In the exam m s-1 will allways have a space between the m and the s. If there is no space the unit is then milliseconds.
| Prefix | Symbol | Power of 10 | Multiplier |
|---|---|---|---|
| Giga | G | 9 | × 109 |
| Mega | M | 6 | × 106 |
| Kilo | k | 3 | × 103 |
| milli | m | -3 | × 10-3 |
| micro | μ | -6 | × 10-6 |
| nano | n | -9 | × 10-9 |
Margaret uses an electronic timer to find out how fast a ball bearing is moving. The ball bearing has a diameter of 8.0 mm. The ball bearing passes through the electronic timer in a time of 2.0 ms. Calculate how fast the ball bearing is moving.
Notice that both of the measurements have the milli prefix (m). This means that both numbers will need to be multiplied by 10-3.
d = 8.0 mm = 8.0 × 10-3 m
t = 2.0 ms = 2.0 × 10-3 s
v = ?
From the relationship sheet we see that the appropriate equation is
Substituting in our values gives
Throughout the rest of this web site you will see the use of these prefixes in relevant contexts. Remember you need to learn the name, symbol and multiplier (use the
Flashcards on unit prefixes
Significant Figures
In most national 5 questions the number of significant figures in the numbers in the question is either 2 or 3. You should read the question carefully and in your final answer write the rounded number to the same number of significant figures.
More details will appear as this site develops.