Question

The least count of 1m rod is
a) 1mm
b) 1cm
c) 1m
d) None of these

Answer 1

Least count of any scale, or an object which can be used to measure the dimensions, is defined as the smallest measurement that can be made using the scale or an object. It is given in the question that the rod is 1m in length. Hence from the above definition of least count of an instrument, it becomes clear what is the minimum measurement one can make from a 1m rod.

Complete step by step answer:
Let us first understand a little more about a least count of a scale.
Let us consider a straight object of length N units. Here the length of the object is measured using some other standard scale and N units represent some standard units used for measurement. Now let us divide the object into 10 equal parts. The minimum reading we can now take using this object of any other body is $\dfrac{N}{10}$. This is also now the least count of the straight object and can now be used as a scale to take a minimum reading of $\dfrac{N}{10}\text{ units}\text{.}$
The above rod is of length 1m, is not divided into any number of equal parts. Hence, the minimum reading one can take using the rod of 1m is 1m itself. Hence the least count of the rod is 1m.

Hence we can conclude that the correct answer is option c.

Note:
It is to be noted that one can take minimum reading 1cm as well as 1mm using the 1m rod if we divide the rod as required. We cannot actually take more minimum reading than 1mm using a 1m rod cause in reality it is not possible to divide a rod more than a thousand times. If we divide also, it will not be properly visible to the human eye.