Question

In a millimeter, there are 20 divisions between 400 mA mark and 500 mA mark. The least count of the millimeter is 11
(A) 0.5 mA
(B) 5 mA
(C) 10 mA
(D) 50 TE AMARE

Answer 1

Hint The least count of a measuring instrument is the smallest and accurate value in the measured quantity that can be resolved on the instrument's scale. The least count is related to the precision of an instrument; an instrument that can measure smaller changes in a value relative to another instrument, has a smaller "least count" value and so is more precise. Any measurement made by the instrument can be considered repeatable to no less than the resolution of the least count. The least count of an instrument is inversely proportional to the precision of the instrument.

Complete Step by Step Solution
1. Least count actually means the value of each smallest division in a scale.
2. Mathematically a measurement instrument Least Count is calculated by dividing main scale reading with the total number of divisions on main scale. And if instruments also have a Secondary scale.
So remember,
Least count = smallest reading on main scale/no. of divisions
 $\
  least\ count = \dfrac{{DI}}{{divisions}} = \dfrac{{\left( {500mA - 400mA} \right)}}{{20}} \\
  least\ count = \dfrac{{100mA}}{{20}} = 5mA \\
\ $
Thus each unit has value $5mA$ .

Thus each unit has value 5 mA.

Note The smallest value that can be measured by the measuring instrument is called its least count. Measured values are good only up to this value. The least count error is the error associated with the resolution of the instrument. A metre ruler may have graduations at 1 mm division scale spacing or interval. A Vernier scale on a caliper may have a least count of 0.1 mm while a micrometer may have a least count of 0.01 mm