Physics SCREW GAUGE

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SCREW GAUGE

Screw Gauge

Screw gauge is a device which can measure very small lengths (or thickness) up to one – hundredth part of a millimeter. It can be used to measure diameter of a wire, thickness of a thin metal sheet, etc.

A Screw Gauge is shown here and its main parts are described below.

`text(Frame -)` It consists of U shaped metallic frame.To one side of this U frame there is a long hollow cylindrical tube with a nut inside it, the inner side of cylindrical nut contains a uniform thread cut in it.On the other side of U frame a fixed stud with a plane face is attached.

`text(Main scale -)` The extended portion of the nut , graduated in millimeters or half millimeters is called the main scale. It has a base line along the axis of the nut.

`text(Thimble -)` The hollow cylinder at the end of the screw is called thimble.

`text(Circular scale -)` The graduated head of the thimble is called circular scale (C.S.).The CS is generally divided into 50 or 100 equal divisions.

`text(Ratchet -)` The ratchet avoids undue tightening of the screw and helps in holding the object between the stud and the end of the screw.

Screw gauge is a device which can measure very small lengths (or thickness) up to one – hundredth part of a millimeter. It can be used to measure diameter of a wire, thickness of a thin metal sheet, etc.

A Screw Gauge is shown here and its main parts are described below.

`text(Frame -)` It consists of U shaped metallic frame.To one side of this U frame there is a long hollow cylindrical tube with a nut inside it, the inner side of cylindrical nut contains a uniform thread cut in it.On the other side of U frame a fixed stud with a plane face is attached.

`text(Main scale -)` The extended portion of the nut , graduated in millimeters or half millimeters is called the main scale. It has a base line along the axis of the nut.

`text(Thimble -)` The hollow cylinder at the end of the screw is called thimble.

`text(Circular scale -)` The graduated head of the thimble is called circular scale (C.S.).The CS is generally divided into 50 or 100 equal divisions.

`text(Ratchet -)` The ratchet avoids undue tightening of the screw and helps in holding the object between the stud and the end of the screw.

Principle of the screw gauge

The screw gauge works on the principle of screw.

When a screw is rotated in a nut, it exhibits both linear and rotational motions.

When a screw is moved in a fixed nut , the linear distance travelled by the screw on the main scale when the circular is given one complete rotation is called `text(Pitch of the screw)`.

`text(Least count of the screw gauge)`

`text[Least count (L.C) =] text(Pitch of the screw) / text(Total number of divisions on the circular scale)`

Generally , the pitch of the screw gauge is 1 mm and it has 100 divisions on its circular scale .

Hence , L.C. = 1 mm / 100 = 0.01 mm or 0.001 cm

`text(Determination of the diameter 'd' of a wire)`

Place the wire between the stud and spindle end as indicated in the diagram.

Rotate the thimble until the wire is firmly held between the stud and the spindle.

The ratchet is provided to avoid excessive pressure on the wire. It prevents the spindle from further movement - squashing the wire!.

To take a reading first look at the main scale and note the main scale reading (M.S.R).

Note the division of the circular scale which coincides with the base line of the main scale. This circular scale division (C.S.D) when multiplied by the least count(L.C) ,gives the circular scale reading(C.S.R)

Add the Main scale reading (M.S.R) and the circular scale reading (C.S.R).This gives the observed reading.

`text(Observed reading = M.S.R. + C.S.R.)`

OR

`text[Observed reading = M.S.R. + (C.S.D. x L.C.)]`

The screw gauge works on the principle of screw.

When a screw is rotated in a nut, it exhibits both linear and rotational motions.

When a screw is moved in a fixed nut , the linear distance travelled by the screw on the main scale when the circular is given one complete rotation is called `text(Pitch of the screw)`.

`text(Least count of the screw gauge)`

`text[Least count (L.C) =] text(Pitch of the screw) / text(Total number of divisions on the circular scale)`

Generally , the pitch of the screw gauge is 1 mm and it has 100 divisions on its circular scale .

Hence , L.C. = 1 mm / 100 = 0.01 mm or 0.001 cm

`text(Determination of the diameter 'd' of a wire)`

Place the wire between the stud and spindle end as indicated in the diagram.

Rotate the thimble until the wire is firmly held between the stud and the spindle.

The ratchet is provided to avoid excessive pressure on the wire. It prevents the spindle from further movement - squashing the wire!.

To take a reading first look at the main scale and note the main scale reading (M.S.R).

Note the division of the circular scale which coincides with the base line of the main scale. This circular scale division (C.S.D) when multiplied by the least count(L.C) ,gives the circular scale reading(C.S.R)

Add the Main scale reading (M.S.R) and the circular scale reading (C.S.R).This gives the observed reading.

`text(Observed reading = M.S.R. + C.S.R.)`

OR

`text[Observed reading = M.S.R. + (C.S.D. x L.C.)]`

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