Question

If the size of bacteria is 1 micron, what will be the number of it in 1 m length?
A. one hundred
B. one crore
C. one thousand
D. one million

Answer 1

Hint: Length is a measure of the distance or shape of a body. We use some other units also to measure the length of very small objects. We can convert the unit from one to another by using suitable expressions.

Complete step by step answer:
Length can be defined as the size of an object or distance from one point to another. We have different units of length in different unit systems. The SI unit of length is meter.
Micron is a unit of length used to describe the length of any object in a very small scale. It is a very small unit of length. It is used conventionally to measure the size of objects like bacteria which are very small. A micron can be defined as the one-millionth of a meter or one twenty-five thousand of an inch. A micron is the same unit as micrometre.
We have,
$\begin{align}
  & 1m=100cm={{10}^{3}}mm={{10}^{6}}\mu m \\
 & 1\mu m={{10}^{-6}}m \\
\end{align}$
Since, the micrometre and the micron are the same unit of length, one micron can be written in metre as,
$1\text{ micron = 1}{{\text{0}}^{-6}}\text{ metre}$
So, if the size of the bacteria is 1 micron, in meters we can write that the size of the bacteria is ${{10}^{-6}}$ metre.
So, in 1 meter of length, the number of bacteria will be,
$n=\dfrac{1m}{{{10}^{-6}}m}={{10}^{6}}$
So, there will be one million bacteria in 1 metre of length.

So, the correct answer is “Option D”.

Note:
In different unit systems we use different units to measure the length of a system. In the fps system, foot is the unit of length. In the CGS unit system, centimetre is the unit of length. It also has other conventional units such as miles, inches etc.