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Wednesday, February 10, 2010

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.

17 comments:

  1. is deci 10 raisec to power -1 or -2

    ReplyDelete
  2. is deci raised to power -1 or -2

    ReplyDelete
  3. deci is 10 raised to -1
    centi is 10 raised to -2
    milli is 10 raised to -3

    ReplyDelete
  4. In physics, is there any rule that says that the numerical part of the answer must be in standard form?
    e.g. 500MW or 0.500GW? Are both accepted?
    Thank you.

    ReplyDelete
  5. There is not a specific rule.

    However there is a rule in mathematics that states that in standard form, the number must be written as follows:

    5800 = 5.8 x 10^3

    Hence it must be written as shown A x 10^B
    where A ca be equal or greater than 1 but less than 10.

    Hence you cannot write it as 58 x 10^2.

    In some rare cases it may be written as shown but it is better to follow the rule in mathematics as described above. Remember that maths in the language of physics.

    ReplyDelete
  6. what is the easiest way to learn these prefixes.?

    ReplyDelete
  7. what is the easiest way of learning these prefixes..??

    ReplyDelete
  8. These are the parts of physics where some rote learning is inevitable.

    But with some good general knowledges someone can
    make the learning easier.

    For the prefixes greater than one knowledge in computers like kilobytes, megabytes, gigabytes can help.

    For smaller ones milimetres can help.

    But apart from those some rote learning and practice is required.

    Keep in mind that in a good physics course you will meet them often and by the time you reach the end of the course you will know them all.

    ReplyDelete
  9. Why 10 raised -6 or -9?For the prefix of the wavelength for red light?Can't other prefixes be used?

    ReplyDelete
  10. about my question posted on 12November...
    I mean, must the numerical number in an answer with a prefix behind, e.g. "500" in "500MW", be between 0 and 10 ? Or is 500MW, 1100km etc allowed in physics?
    Or must it be 0.5GW (as 0.5 is between 0 and 10), Thanks!

    ReplyDelete
  11. For my question posted on 12 November...
    I mean, must the numerical part of an anwer with a prefix attached behind, eg. "500" in "500MW" be between 0 and 10? Meaning are answers like 500MW, 1100km etc allowed?
    Or must it be 0.5GW (as 0.5 is between 0 and 10)? Thanks!

    ReplyDelete
  12. Is there any book in which physics is basic and world famous queries are easily explained can u tell me that book name please

    ReplyDelete
  13. thank you for examples that show me what is prefix in physics .


































    student in the faculty of science
    A.H.

    ReplyDelete
  14. How do you remove prefixes such as 20cm

    ReplyDelete
  15. good idea physics student take many help from this website

    ReplyDelete

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