# To measure the thickness of a given sheet using screw gauge

With Vernier Callipers, one is able to measure the length accurately up to 0.1 mm. More accurate measurements up to 0.01 mm or 0.005 mm, may be done using a screw gauge. Screw gauge is an instrument with higher precision than the vernier calliper. Here, in the experiment, we will be discussing how to measure the thickness of a given sheet using screw gauge.

## Aim

To measure the thickness of the sheet using screw gauge.

## Apparatus/ Materials Required

• Screw Gauge
• Sheet
• Magnifying Lens

## Theory

Screw gauge is an instrument used to accurately measure the thickness of a sheet of metal. It is comprised of a U-shaped frame fitted to a screwed spindle which is attached to a thimble. A scale graduated in mm is engraved parallel to the axis of the thimble. This is known as the pitch scale. The head of the screw consists of a rachet that avoids undue tightening of the screw. On the thimble, there is a circular scale known as the head scale which is divided into 50 to 100 equal parts. The pitch of the screw is the distance moved by the spindle per revolution. The distance moved by the tip of the screw when the screw is turned through 1 division of the head scale is known as the least count.

Formula:

• $Pitch\, of\, the\, Screw=\frac{Distance\,moved\,by\,the\,screw}{No\,of\,full\,rotations\,given}$
• $Least\,Count=\frac{Pitch}{Total\,Number\,of\,Divisions\,on\,the\,Circular\,Scale}$

## Procedure

• Insert the sheet between the studs of the screw gauge and determine the thickness at five different positions.
• Find the average thickness and determine the correct thickness by applying the zero error.

## Observations

Least count of the screw gauge = ….. mm

Zero Error of screw gauge = ….. Mm

 S.No Linear Scale Reading M (mm) Circular Scale Reading n Thickness t = M + n × L.C (mm) 1 2 3 4 5

Mean thickness of the given sheet = ….. mm.

Mean corrected thickness of the given sheet = Observed thickness – Zero error = …… mm.

## Result

The thickness of the given sheet is …..m.

## Viva Voice

1. What is meant by the pitch of a screw?

Answer: The distance between two nearest threads along the axis of screw is known as the pitch of the screw.

2. What is the least count of the screw gauge?

Answer: The least count of the screw gauge is 0.001 cm.

3. What is meant by the zero error of a screw gauge?

Answer: The error that arises when the zero of circular scale does not coincide with the zero of the main scale upon joining the two studs.

4. When is the zero error positive?

Answer: If the zero of the circular scale lies above the reference line, provided that the fixed and movable studs are in contact.

5. What is meant by the range of the screw gauge?

Answer: The maximum length of the main scale is known as the range of the screw gauge.

6. Does the diameter of the screw depend on the temperature?

Answer: Yes, the diameter of the screw depends on the temperature. When the temperature increases the diameter of the screw increases.

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