9th Class Physics Notes “Working & Verniercalliper”

Working:

Let we have a meter rule and we want to measure the length of a book with help of meter rule, we have to place our eyes vertically above the mark reading. If we do not kept our eye vertically above the meter ruler then certain error occur in the measurement called parallax error, to improve accuracy, take several reading, and use the average of these readings for better result.

Figure:

meter rule with parallax error

Example:

If we want to measure the length of pencil, we take three reading from different position; in first case we read that length of pencil is 14cm at position (1). Form position (2) which is vertically above we read 15cm, and from position (3) we reads the length of pencil 16cm in all the three reading the position (2) reading is correct because it is vertically above the point and in this reading there is no parallax error, In order to take more accurate reading we take more reading and finally take their average.

Q:Explain the construction and working of vernier calliper.

Verniercalliper:

Definition:

An instrument which is used to for the measurement of short length up to 0.01cm or 0.1mm accurately is known as verniercalliper.

Inventor:

Verniercalliper was invented in 1631 by a French mathematician Pierre Vernier.

Purpose:

Verniercalliper is used to measure the thickness, diameter or the width of an object and the internal, external diameter of hollow cylinder, and depth.

Construction:

Veniercalliper consists of:

• Two lower jaws (used for the measurement of external diameter)
• Two upper jaw (used for the internal diameter)
• Needle (used the measurement of depth)

Scale of verniercalliper:

There are two scale of venire calliper,

1. Main scale.
2. Vernier scale.

Verniercalliper:

1. Main scale: Main scale is in the form of steel bar and is graduated in centimeter and millimeter.
2. Vernier scale: Vernier scale can slide over the main scale. It has the length of 9mm, and divided equally into 10 divisions. The separation between two venire lines is 0.9mm.

Least count of vernier constant:

The difference between one main scale division and one vernier division is called vernier constant or least count.

OR
The minimum length which can be measured with help of veniercalliper is called least count.

There two method for finding the least count of venire calliper.

Method of finding least count:

First method:

Least count of verniercalliper is equal to the difference b/w one main scale division and one vernier scale division i.e.

One main scale division = 1mm
One vernier scale division = 0.9mm

Least count = 1mm – 0.9mm
Least count = 0.1mm
Or least count = 0.01cm

2nd method:

Least count of veniercalliper can also be found out mathematically by following method.

Least count = value of smallest division on main scale / total number of division of vernier scale