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Government Polytecnic, Jamnagar.

Practicals in Physics

By

Dr. U M Joshi

Lecturer in Physics

EXPERIMENT - 2

LINEAR DIMENSION BY MICROMETER SCREW

Experiment - 2 A

Aim: To measure the volume of a given wire.

INSTRUMENT/MATERIAL:

1 Micrometer screw gauge.

2 A metallic wire

3 Vernier calipers

IMAGE OF MICROMETER SCREW Courtesy: Miniphysics

IMAGE OF MICROMETER SCREW Courtesy: https://www.cyberphysics.co.uk/practical/skills/micrometer.htm

Theory of Micrometer Screw gauge

Theory:

The micrometer screw gauge is an instrument used for measuring precisely the diameter of a thin wire or thickness of metal sheet.

It consists of a U-shaped frame fitted with a screwed spindle which is attached to a thimble.

Pitch of the screw

Pitch:

Pitch of the screw gauge is defined as the distance between two consecutive threads of the micrometer screw. It is denoted as p.

Image of micrometer screw pitch

Least count formula of micrometer screw

Least count = Pitch =p/n

Number of division on head scale

Where p= pitch of the screw

n= number of divisions on head scale or

circular scale

Least count of = (0.5 mm)/(50) = 0.01 mm

Image of micrometer screw

Micrometer

Micrometer

Video Link of micrometer screw gauge

• https://youtu.be/_NbQV9OEsoQ

• https://youtu.be/phFRSS7mH9Y

• https://youtu.be/tMILwd6mkfE

• https://youtu.be/TD5wM9Q6BAk

• https://youtu.be/7g_JE9dxEuw

Error in Micrometer screw

Zero Error :

When the anvil face & spindle are just in contact with ratchet and If the base line of the main scale coincides with the zero of the head scale (circular scale) than error is known as zero error

Image of Zero error

Positive Error:

When the anvil face & spindle are just in contact with ratchet and If zero of the head scale (circular scale) below the base line of the main scale than error is known as positive zero error

Error in Micrometer screw

Image of positive error

Error in Micrometer screw

Negative Error:

When the anvil face & spindle are just in contact with ratchet and If zero of the head scale (circular scale) above the base line of the main scale than error is known as negative zero error

Image of Negative Error

Image of all Error in micrometer

Image of all Error in micrometer

Virtual Lab link for Micrometer

• http://amrita.olabs.edu.in/?sub=1&brch=5&sim=156&cnt=4

Procedure of Exp – 2A

Procedure :

(1) Determine the pith of the screw and record it.

(2) Count the number of division (n) on the head

scale

(3) Least count (LC) = Pitch

Number of division on head scale

=p/n

(4 ) Determine the zero error C’ of the screw and obtain

the correction C.

(5 ) Hold the wire between the flat ends A and B of the

screw .

(6) Find out which division of main scale touches the edge

of head scale and consider it as a main scale reading A

(7) Now note the number n of head scale or circular scale

which coincides with base line. Multiply n with L.C.

and considered as head scale reading B.

(8) Measure the diameter of the wire at three different

places of the wire and calculate the average diameter .

(9) Do the correction in the average value if there is zero

error either positive or negative.

(10) Measure the length of wire with the vernier caliers.

Procedure of Exp – 2A

• OBSERVATION:

• Pitch of the micrometer screw (p) = 0.5 mm

• Number of division on head scale (n) = 50

• Least count x = p/n = 0.5/50 = 0.01 mm

• Zero error positive/negative c’ = 0.00

• Correction c = 0.00

Procedure of Exp – 2A

Table by micrometer

Dimension of object

No.of obs.

Main scale obs. A mm

Head scale obs. Div.On Its value Head scale B= N×X N

Value of dimension D’=A+B

Average value D’ mm

Corrected value D=D’±C mm

Diameter of wire

1 2 46 0.46 2.46 2.19 2.19+ 0.00= 2.19

2 2 6 0.06 2.06

3 2 6 0.06 2.06

Table by vernier

Dimension of object

No. of obs.

Main scale obs A mm

Vernier scale obs. coincident Its value

Mark B=N×x

Value of dimension L’= A+B

Average Value L ‘

Corrected value L=

Length of wire

1 13.00 0.00 0.00 13 13 13.00 mm 2 13.00 0.00 0.00 13 13

3 13.00 0.00 0.00 13 13

Calculation

Volume of wire v= Π D2L

4

=3.14 x (2.19)2 ×13

4

= 484.44 mm3 =484.44/1000

= 0.484 cm3

1mm=1/10cm

1mm3 =1/10x1/10x1/10=1/1000

EXPERIMENT 2 B

Aim: To measure the volume of rectangular block by measuring thickness by micrometer screw and length and breadth by vernier calipers.

INSTUMENT/MATERIL : 1 Micrometer screw

2 A rectangular block

3 Vernier calipers

Procedure :

(1) Measure least count and zero error

correction in micrometer.

(2 )Hold the thickness of metallic piece

between two flat ends of micrometer.

(3 )Take main scale reading A and record it

(4)Find the coincident mark with base line

and record it.

(5 )Find the reading on head scale record as B

Procedure of Exp – 2B

(6 ) Take the readings for three times.

(7) Find average value & correct value of thickness .

(8 ) Compare the thickness obtained by vernier caliper and

micrometer.

(9) Calculate volume of rectangular block with the help of

readingslength (L) and breadth (b )from experiment 1B

Observation : micrometer screw Range = 0 to 25 mm

Least count(LC) = p/n

=0.5/50

=0.01 mm

Correction C’= +0.00

Procedure of Exp – 2B

Observation Table

Dimension of object

No. of obsearvation

Main scale obs. A mm

Vernier scale Observation Coincident Its mark N Value B= N×X

Value of Dimension H=A+B

Average Value H mm

Corrected value Y= H±c

Thickness

1 5 11 0.11 5.11 5.19 5.19+0.00=5.19 2 5 34 0.34 5.34

3 5 13 0.13 5.13

Dimension of wire

No. of obs.

Main scale Obs A mm

Vernier scale obs. Coincident Its Mark Value N B=N×X

value of Dimension l ’=A+B/ b’=A+B

Average Value l’/b’ mm

Corrected value l=l’+c B=b’+c

Length 1 47 30 0.60 47.60 47.235 47.24

2 47 28 0.56 47.56

3 46 30 0.60 46.60

Breadth 1 11 40 0.80 11.80 11.44 11.44

2 11 11 0.22 11.22

3 11 15 0.30 11.30

Calculation of Exp- 2B

Volume of rectangular block with micrometer screw

= l X b X h

=47.24 X 11.44 X 5.19

= 2805.40 mm3

= 2.805 cm3

Questions

(1 ) why is instrument named as micrometer screw ? Ans: The micrometer screw gauge works on the principal of a perfect screw fixed in a nut. (2 )Explin the terms (1) pitch (2) least count Ans: (1) pitch of the screw is the distance between two consecutive threads of the screw.

(2) Least count = pitch (p)

Number of Division on head scale (n)

(3)When is zero error said to be positive or negative ?

Ans: If the zero of the head scale stands blow the base line is

called positive error & if the zero of the head scale stand

above the base line ,the error is said to be negative.

(4) Fill up the gap:

(1) 1 micrometer = 10-6 meter (2) 1 millimeter = 10-3 meter

(3) 1 Nanometer = 10-9 meter (4) 1 meter =1010 angstrom

Questions

THANK YOU