2

EXPT NO: 2. USE OF MICROMETER SCREW GAUGE

Aim :  To measure cross sectional area of uniform wire and the thickness of plate.

Apparatus : Micrometer screw gauge, plate, a metal wire of uniform diameter.

Diagram :

Screw Gauge

Formula : Pitch of micrometer screw gauge.

 Least count of micrometer screw gauge.

Procedure :                To find the least count of screw gauge :

·         Note the value of the smallest division on main scale of screw gauge.

·         Coincide the zero of circular scale with reference line and note the main scale reading.

·         Rotate the screw to complete 5 full rotations. Again note down the main scale reading.

·         The difference between these two main scale readings gives the distance covered by the screw tip in 5 rotations. Then calculate pitch of micrometer screw gauge.

·         Then, note down the total number of divisions of circular scale (N)

·         Finally, calculate least count of the micrometer screw gauge.

:To find the zero error :

·         Bring the two jaws of gauge in contact with each other.

·         Observe and conclude according to the following given conditions.

·         If zero of circular scale coincides with reference line.

There is no zero error. (Z) = 0

·         If zero of circular scale is below reference line. If nth division of circular scale coincides with reference line.

There is Positive error (Z) = + (n x L.C)

·         If zero of circular scale is above the reference line.  If nth division of circular scale coincides with reference line and N is total number of division on circular scale.

There is negative error (Z) = [(N - n) x L.C.]

:To determine the diameter of wire :

     Hold the wire between the jaws of micrometer and note down the following :

      Note the main scale reading (A)

            Note the circular scale division that coincides with reference line (B).

      Then, calculate the total reading (T) with the following formula C = A + (B x L.C.)

      Take three independent readings for different positions of the wire.

      Find the corrected reading according to the zero error (T=C + Z) and find the mean value of diameter of wire.

Find the thickness of plate in similar manner.

Observations:

Number of rotations to screw                              n          =………………..

Distance advanced by screw in N rotations        X         =………………..

Pitch of the screw (P = X/n)                                 P          =………………..

Total number of divisions on the circular scale N        =………………..

Least count of screw gauge                      L.C=(P/N)      =………………..

Zero error  (positive/negative)                 Z                      =………………..

Observation Table :

Diameter of the wire / thickness of the plate.

Object	Obs No	Dimension	Main Scale reading A cm	Circular Scale reading B	Total reading C=A+(BxL.C)	Corrected reading T=C+Z cm	Mean reading cm
Wire	01	Diameter
	02
	03
Plate	01	Thickness
	02
	03

Calculations :

Least Count :

Value Log p=3.14 Log3.14=………… R= Log(         )=…….. R= Log(         )=…….. Y   =   +  A=  Antilog Y A  =

Results :          i)      Cross sectional Area                 =…………..cm²

                        ii)      Thickness of Plate                    =……………..cm

 Precautions :

      While rotating the micrometer screw, do not apply an excessive pressure on the object.

      Use the ratchet to avoid the excessive pressure.

      The screw sleeve should not be rotated instead of its head.

      The screw should move freely without friction.

      The zero correction, with proper sign should be noted very carefully and added or subtracted.

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