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Order Of Magnitude

The order of magnitude of a number is the power of ten closest to the number.

Following table gives us some of the commonly used prefixes for power of ten.

Positive Powers of 10

S. No. Prefix Symbol Multiplier Factor Power of 10
1. Yotta Y 1024 24
2. Zeeta Z 1021 21
3. Exa E 1018 18
4. Peta P 1015 15
5. Tera T 1012 12
6. Giga G 109 9
7. Mega M 106 6
8. Kilo K 103 3
9. Hecto H 102 2
10 Deca Da 10 1

Negative Powers of 10

S. No. Prefix Symbol Multiplier Factor Power of 10
1. Yocto Y 10-24 -24
2. Zepto z 10-21 -21
3. Atto a 10-18 -18
4. Femto f 10-15 -15
5. Pico p 10-12 -12
6. Nano n 10-9 -9
7. Micro 10-6 -6
8. Milli m 10-3 -3
9. Centi c 10-2 -2
10 Deci d 10-1 -1

Some Derived SI units and their symbols

Quantity Unit Symbol Expressed in base units
Force Newton N Kg-m/sec2
Work Joules J Kg-m2/sec2
Power Watt W Kg-m2/sec3
Angular momentum Kg m2s-1
Pressure Pascal Pa Kg m-1/s2
Wavelength m

The following conventions are adopted while writing a unit.

  • Even if a unit is named after a person the unit is not written in capital letters. i.e. we write joules not Joules.

  • For a unit named after a person the symbol is a capital letter e.g. ‘J’ for joules and the rest of them are in lowercase letters e.g. ’s’ for seconds.

  • The symbols of units do not have plural form i.e. 70 m not 70 ms or 10 N not 10 Ns.

  • Not more than one solid’s is used i.e. all units of numerator is written together before the ‘ / ‘ sign and all in the denominator are written after that.

i.e. It is 1 ms-2 or 1 m/s2 not 1m/s/s.

  • Punctuation marks are not written after the unit e.g. 1 litre = 1000 cc not 1000 c.c.

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