Question

The prefix femto stands for:
(A) $ {10^9} $
(B) $ {10^{ - 12}} $
(C) $ {10^{ - 15}} $
(D) $ {10^5} $

Answer 1

Hint: To answer this question, you must recall the prefixes of SI units. SI units stands for Standard international units and it is clear from the name that these are the units that are accepted internationally as standard units of measurement.

Complete step by step solution
Prefix is a word that is written before a meaningful word to make another meaningful word. A prefix, may or may not be a meaningful word. For example let us consider meter as a word. So if we attach centi as the prefix in the beginning of the word meter, we get a centimeter. Centi means 100. We know that 100 centimeters make up one meter. This is how the system of units works. Each prefix added before a unit like meter or gram refers to some order of magnitude. Like in case of centimeters, the prefix centi- refers to the order of $ - 2 $ , that is, $ {10^{ - 2}} $ .
Similarly, femto is a prefix used in the system of units and it refers to the order of $ - 15 $ . In other words, the prefix femto stands for $ {10^{ - 15}} $ . It is derived from a Danish word ‘femten’ which means fifteen thus referring to the order that it carries. It is referred to as fm in short.
The correct option is A.

Note
The SI units are also referred to as MKS units where M represents meters as the SI unit for measurement of length, K represents kilograms as the SI unit for measurement of mass and S represents seconds as the SI unit for the measurement of time.