Question

One micrometer is equal to
\[
  \left( A \right){\text{ }}0.0001{\text{ }}mm \\
  \left( B \right){\text{ }}0.001{\text{ }}mm \\
  \left( C \right){\text{ }}0.01{\text{ }}mm \\
  \left( D \right){\text{ }}0.00001{\text{ }}mm \\
 \]

Answer 1

Hint: Length is a fundamental quantity which is measured by metre. Some other units of measurement are there, out of which micrometer is one. Micrometer is related with other units like cm, dm, mm, etc.

Complete answer:
Micron is small unit and is related with metre as:
$1\,micrometer = \dfrac{1}{{1000000}}metre$
$ = {10^{ - 6}}metre$……………………..……(i)
Also $1\,metre = \,1000\,mm$……..….(ii)
From $e{q^n}$ I and II
$
  1\,micrometer\, = \,{10^{ - 6}} \times \,1000\,mm \\
   = \,{10^{ - 3}} \\
   = \,0.001\,mm \\
 $

Hence, option (B) is correct. So, one micron is equivalent to $0.001mm$

Additional Information: To calculate length of various objects depending on their size we have to use different units but these units are related to each other. e.g.
\[
  {10^3}\,m = \,1\,km \\
  {10^2}\,m\, = \,1\,hectometer \\
  10\,m\, = \,1decameter \\
  1\,m\, = 10\,dm \\
  1\,m\, = 100\,cm \\
  1\,m\, = 1000\,mm \\
  1\,nm\, = {10^{ - 09}}m \\
  1\,A^\circ \, = \,{10^{ - 10}}m \\
  1\,pm\, = \,{10^{ - 12}}m \\
  1\,F\, = \,{10^{ - 15}}m \\
 \]$$

Note: All length units are inter related with each other and they vary in powers of 10. So, students must know how to calculate the numerical based on powers of 10. They know the basic rules of BODMAS. There are different objects either living or non-living out of which some are bigger and some are tiny microscopic for example bacteria, viruses, and other microscopic organisms. Their size is always measured in micron, picometer, nanometer, etc. These units are not fundamental units but they represent the size of organisms precisely and they are preferred conventionally. So rather than using metre, these alternative units are used. Students must know the conversions related to each other in order to avoid mistakes. If silly mistakes are done, this results in higher percentage error in the calculation which will be far away from the exact value.