Question

On the main scale of a travelling microscope 1cm is divided into 20 divisions. What is the least count of the main scale of this device?

Answer 1

Hint: Least count is the smallest measurable value on the instrument. Main scale readings are further divided into smaller divisions. The value of this smallest division is the least count.

Complete Step-by-Step solution:
Least count of an instrument:
The smallest value that can be measured by an instrument is called ‘Least count of that instrument’. For example using a ruler we can measure the smallest length of 1mm, so 1mm is a least count of ruler. The least count describes the precision of an instrument. We cannot measure values which are smaller than least count.
How to calculate least count:
We can calculate the least count of main scales by dividing the smallest reading on the main scale by the number of divisions between two main scale readings.
For a given question the smallest reading on the main scale is 1cm and there are 20 divisions between two main scale readings.
Therefore,
$\begin{align}
  & L.C.=\dfrac{1cm}{20} \\
 & L.C.=0.05cm \\
\end{align}$
So the Least count of travelling microscopes is 0.05cm.

Additional Information:
If the instrument has a secondary scale then least count can be calculated by dividing main scale least count with the number of divisions on the secondary scale.
Accuracy and precision are directly related with least count.

Note: The least count describes the smallest value that can be measured by an instrument. It is the smallest interval in measured quantity while taking measurements. For example the least count of rulers is 1mm so quantities measured using a ruler have an interval of 1mm.