Least Count

The least count of an instrument is the smallest measurement that can be taken accurately with it. The least count of meter scale is 1mm, and that of the ammeter shown below is 2 ampere.

Measurement of length with a meter scale

In daily life, the length is measured with the help of a meter scale. It is graduated in cm and mm such that the value of one small division is 1 mm. Thus a meter scale can be used to measure a length accurately up to 1 mm.

Vernier Callipers

Vernier callipers, an instrument for making very accurate linear measurements were introduced in 1631 by Pierre Vernier of France. Vernier Calipers are widely used in scientific laboratories and manufacturing for quality control measurements.

Vernier Calliper Parts

1. Main Scale – The main scale is similar to that on a ruler, graduated in mm and cm on one side; inches on the other side.

2. Vernier Scale – The vernier scale is a sliding scale. It slides parallel to the main scale and enables readings to be made to a fraction of a division on the main scale. The total number of divisions on the vernier scale is 100.

3. Screw – The vernier scale can be fixed at any position on the main scale with the help of a screw.

4. Jaws – It has two jaws. The lower jaws are called outside jaws, and they are used to measure the length of a rod the diameter of a sphere or the external diameter of a cylinder. The upper jaws are called the inside jaws which are used to measure the internal diameter of a hollow cylinder or pipe.

5. Strip – The thin strip is used to measure the depth of the objects like beakers.

Least count of Vernier Calliper

Least count of Vernier calliper= Smallest division on main scale/Number of divisions on Vernier scale.

Least count of Vernier calliper = 1mm/10 divisions

Least count of Vernier calliper = 0.1 mm

Uses of a Vernier Calliper

Vernier callipers are used to measure;

(i)The length of a rod or any object

(ii)The diameter of a sphere

(iii)The internal and external diameter of a hollow cylinder

(iv)The depth of a small beaker.

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