# 11th Class Physics Physical World / भौतिक जगत Order of Magnitude

Order of Magnitude

Category : 11th Class

In scientific notation the numbers are expressed as, Number $=M\times {{10}^{x}}$. Where M is a number lies between 1 and 10 and x is integer. Order of magnitude of quantity is the power of 10 required to represent the quantity. For determining this power, the value of the quantity has to be rounded off. While rounding off, we ignore the last digit which is less than 5. If the last digit is 5 or more than five, the preceding digit is increased by one. For example,

(1) Speed of light in vacuum

$=3\times {{10}^{8}}m{{s}^{-1}}\approx {{10}^{8}}m/s$   (ignoring 3 < 5)

(2) Mass of electron $=9.1\times {{10}^{-31}}kg\approx {{10}^{-30}}kg$  (as 9.1 > 5).

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