I WANT MORE INFORMATION AND VIVA QUESTIONS ABOUT PHYSICS PRACTICALS ESPECIALLY ABOUT SCREW GUAGE ,VERNIER CALIPERS,SIMPLE PENDULUM ,VELOCITY OF SOUND AND SPEHERO METER
To measure the diameter of the given lead shot.
To measure the diameter of a given wire and find its volume.
To measure the thickness of a given glass plate and find its volume.
To measure the volume of an irregular lamina.
The Theory
The screw gauge is an instrument used for measuring accurately the diameter of a thin wire or the thickness of a sheet of metal. It consists of a U-shaped frame fitted with a screwed spindle which is attached to a thimble.
Parallel to the axis of the thimble, a scale graduated in mm is engraved. This is called pitch scale. A sleeve is attached to the head of the screw.
The head of the screw has a ratchet which avoids undue tightening of the screw. On the thimble there is a circular scale known as head scale which is divided into 50 or 100 equal parts. When the screw is worked, the sleeve moves over the pitch scale.
A stud with a plane end surface called the anvil is fixed on the ‘U’ frame exactly opposite to the tip of the screw. When the tip of the screw is in contact with the anvil, usually, the zero of the head scale coincides with the zero of the pitch scale.
Pitch of the Screw Gauge
The pitch of the screw is the distance moved by the spindle per revolution. To find this, the distance advanced by the head scale over the pitch scale for a definite number of complete rotation of the screw is determined.
The pitch can be represented as;
Least Count of the Screw Gauge
The Least count (LC) is the distance moved by the tip of the screw, when the screw is turned through 1 division of the head scale.
The least count can be calculated using the formula;
Zero Error and Zero Correction
To get the correct measurement, the zero error must be taken into account. For this purpose, the screw is rotated forward till the screw just touches the anvil and the edge of cap is on the zero mark of the pitch scale. The Screw gauge is held keeping the pitch scale vertical with its zero down wards.
When this is done, anyone of the following three situations can arise:
The zero mark of the circular scale comes on the reference line. In this case, the zero error and the zero correction, both are nil.
The zero mark of the circular scale remains above the reference line and does not cross it. In this case, the zero error is positive and the zero correction is negative depending on how many divisions it is above the reference line.
The zero mark of the head scale is below the reference line. In this case, the zero error is negative and the zero correction is positive depending on how many divisions it is below the reference line.