**Describe the construction and working of Vernier calipers?**

Difficulty: Hard

**Vernier calipers:**

An instrument used to measure small lengths such as internal or external diameter or Length of a cylinder etc. is called Vernier Calipers.

**Construction: **

A Vernier Calipers consists of two jaws. One is a fixed jaw with the main scale attached to it.

**Main scale:**

The main scale has centimeter and millimeter marks on it. The other jaw is moveable.

**Vernier scale:**

It has a Vernier scale having 10 divisions over it such that each of its divisions is 0.9 mm.

**Least count (LC)/Vernier constant:**

The difference between one small division on the main scale division and one Vernier scale division is 0.1 mm. It is called the least count (LC) of the Vernier Calipers. The least count of the Vernier Calipers can also be found as given below:

Least count of Vernier Calipers = smallest reading on main scale ÷number of divisions on Vernier scale

= 1mm ÷ 10 divisions

** Hence** LC=0.1mm= 0.01 cm

**Working of a Vernier Calipers: **

First of all, find the error, if any, in the measuring instrument. It is called the zero error of the instrument. Knowing the zero error, necessary corrections can be made to find the correct measurement. Such a correction is called the zero correction of the instrument. Zero correction is the negative of zero error.

**Taking a Reading on Vernier Calipers:**

Let us find the diameter of a solid cylinder using Vernier Calipers. Place the solid cylinder between the jaws of the Vernier Calipers. Close the jaws till they press the opposite sides of the object gently.

Note the complete divisions of the main scale past the Vernier scale zero in a tabular form. Next, find the Vernier scale division that is coinciding with any division on the main scale. Multiply it by feast count of Vernier Calipers and add it to the main scale reading. This is equal to the diameter of the solid cylinder. Add zero correction (Z.C) to get the correct measurement. Repeat the above procedure and record at least three observations with the solid cylinder displaced or rotated each time.

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