Prefixes in Physics

You have seen in a previous post that physical quantities are properties of an object that can be measured with a measuring instrument.

Hence when you take the measurement the number that is obtained might be unusually large or small so that it is difficult to work with them. We have already seen such an example with the electron volt.

Hence in order to make working with these numbers we use prefixes. A prefix is a symbol that you place in front of a unit. The prefix will indicate a multiple of the unit.

The table below Let us have a look at a list of prefixes that you may encounter in your physics classes.

Name of prefix	Symbol	Multiple of
Giga	G	x109
Mega	M	x106
kilo	k	x103
Hecto	H	x102
deci	d	x10-2
milli	m	x10-3
micro	μ	x10-6
nano	n	x10-9

So how to use a prefix?

Example 1

Suppose a measurement is made and the result is as shown below.

Power = 2000000 W

Now this power can be rewritten in the form of standard form as shown below:

Power = 2.0 x 10⁶ W

As we have seen in the table the prefix Mega is x10⁶ meaning 1 million.

Hence

Power = 2.0 x 10⁶ W

can be rewritten as

Power = 2.0 (x 10⁶⁾ W

                =2.0 MW

If 1 mega is one million then 2.0MW is 2 million W.

Example 2

The diameter of a cell is 0.000002 m

If you rewrite this in standard form then the diameter will be written like this

diameter = 2.0 x10^-6 m

if you would recall the prefix micro is represented by x10^-6 meaning 1 millionth.

Hence

diameter = 2.0 x10^-6 m

can be rewritten as

diameter = 2.0 x10^-6 m

diameter = 2.0( x10^-6 )m

                    =2.0  μm

If a micro is one millionth then 2.0  μm is 2 millionth of a meter.

However it is also possible that a measurement is taken but it is impossible to write it directly in term of a prefix.

The wavelength of red light= 6.50 x10^-7 m

As you can see it is not possible to write it directly in term of either micro or nano. In this case a division must be performed. If you want to write the wavelength of red light in term of micro then you have to divide the wavelength by 1 x10^-6 but if you want to write it in term of nano you will then have to divide it by 1 x10^-9.

To write the wavelength in term of micro

wavelength = 6.50 x10^-7 m

                        = 6.50 x10^-7/ 1 x10^-6 μm

                        =0.650 μm

To write the wavelength in term of nano 

wavelength = 6.50 x10^-7 m

                        = 6.50 x10^-7/ 1 x10^-9 nm

                        =650 μm

As you can see it is quite easy to write any number in term of prefix. If after this post you still have difficulties, then you can leave your question in the comment section below.