Question

One Fermi is?
(a)- ${10}^{-15}\text{ cm}$
(b)- ${10}^{-13}\text{ cm}$
(c)- ${10}^{-10}\text{ cm}$
(d)- ${10}^{-12}\text{ cm}$

Answer 1

Hint: The value of Fermi is first converted into meters and then it is divided by 100 to get the value in cm. One Fermi in SI unit is equal to 10 raised to the power -15.

Complete answer:
We require units that may be multiples or fraction of the base units. The SI system recommends the multiples such as ${10}^3,{10}^6,{10}^9$ etc and fractions such as ${10}^{-3},{10}^{-6},{10}^{-9}$ etc. These are indicated by special prefixes.
One Fermi is equal to 10 raise to the power -15 meters in SI units:
$\text{one fermi = 1}{\text{0}}^{-15}\text{ m}$
In the question all the options are in centimeter, so to convert meter to centimeter we have to divide it with 100.
$\text{one fermi = }{\displaystyle \frac{{10}^{-15}}{100}}={10}^{-13}\text{ cm}$
So, the correct answer is “Option B”.

Additional Information:
Some of the commonly used units are:
Centimeter (cm): Its prefix is centi and it is equal to ${10}^{-2}\text{ m}$.
Millimeter (mm): Its prefix is milli and it is equal to ${10}^{-3}\text{ m}$.
Micrometer ($\mu m$ ): Its prefix is micro and it is equal to ${10}^{-6}\text{ m}$
Nanometer (nm): Its prefix is nano and it is equal to ${10}^{-9}\text{ m}$
Picometer (pm): Its prefix is pico and it is equal to ${10}^{-12}\text{ m}$
Atto meter (am): Its prefix is atto and it is equal to ${10}^{-18}\text{ m}$
Kilometer (km): Its prefix is kilo and it is equal to ${10}^3\text{ m}$
Mega meter (Mm): Its prefix is mega and it is equal to ${10}^6\text{ m}$
Gigameter (Gm): Its prefix is giga and it is equal to ${10}^9\text{ m}$
Tetrameter (Tm): Its prefix is tetra and it is equal to ${10}^{12}\text{ m}$

Note: You may get confused between option (a) and (b) because in the SI unit Fermi is equal to ${10}^{-15}\text{ m}$ in meter but in the options, a centimeter is given, so it has to be converted into centimeter. Always take care of the conversions while doing the question