General instructions:

1.write diagram, Tabulation and calculation on the unruled paper.

2.Write Aim, Apparatus required, Formula, Formula expansion, Theory, Principle, Procedure, Result,
Precautions and Sources of Error on the ruled Paper.
3.Use scale and pencil to draw diagram and tabulation.

Vernier calliper
Aim:
To measure radius and volume of a small spherical bob using Vernier Callipers
Apparatus:

Vernier callipers, a spherical body (pendulum bob) or a cylinder and a magnifying lens.

Formula:
V.S.R = V.S.C X L.C
O.R = M.S.R + V.S.R
CR = OR -+ ZC
V = (4/3) πr³
Formula expansion:

V.S.C-Vernier scale Coincidence in division

M.S.R - Main scale reading in x10−2m
L.C - Least count x10−2m
C.R-Correct reading x10−2m
O.R =Observed reading x10−2m
V-volume of a sphere in x10−3m
Theory:

If with the body between the jaws, the zero of vernier scale lies ahead of Nth. division of
main scale, then main scale reading (M.S.R.) = N. If nth division of vernier scale coincides
with any division of main scale, then vernier scale reading (V.S.R.)
= n x (L.C.) (L.C. is least count of vernier callipers)
= n x (V.C.) (V.C. is vernier constant of vernier callipers)
Total reading, T.R. = M.S.R. + V.S.R. (L.C. = V.C.) = N + n x (V.C.).
Principle:

The difference in the magnitude of one main scale division and one vernier scale division
[V.S.D] is called the least count of the instrument, as it is the smallest distance that can be
measured using the instrument.

Procedure

1. Determine the vernier constant (V.C.) i.e. least count (L.C.) of the vernier callipers
and record it step wise.

2. Bring the movable jaw BD in close contact with the fixed jaw AC and find the zero
error. Do it three times and record them. If there is no zero error, record zero error nil.

3. Open the jaws, place the sphere or cylinder between the two jaws A and B and adjust
the jaw DB, such that it gently grips the body without any undue pressure on it. Tight
the screw S attached to the vernier scale V.

4. Note the position of the zero mark of the vernier scale on the main scale. Record the
main scale reading just before the zero mark of the vernier scale. This reading (1ST)
is called main scale reading (M.S.R.).

5. Note the number (n) of the vernier scale division which coincides with some division
of the main scale.

6. Repeat steps 4 and 5 after rotating the body by 90° for measuring the diameter in a
perpendicular direction.

7. Repeat steps 3, 4, 5 and 6 for three different positions. Record the observations in
each set in a tabular form.
8. Find total reading and apply zero correction.
9. Take mean of different values of diameter and show that in the result with proper unit.

DIAGRAM:
Observations:

Least count= Zero Error: Zero correction:

S.NO Main scale Vernier scale V.S.R = OR=MSC+VSR CR=OR-+ZC
reading coincidence VSC X LC
[MSR] [VSC]
unit x10−2m division x10−2m x10−2m x10−2m

Result:
The radius of the given sphere________
The volume of the bob is_________
Precautions:
1. Motion of vernier scale on main scale should be made smooth (by oiling if necessary).
2. Vernier constant and zero error should be carefully found and properly recorded.
3. The body should be gripped between the jaws firmly but gently (without undue pres-
sure on it from the jaws).
4. Observations should be taken at right angles at one place and taken at least as three
different places.
Sources of Error:
1. The vernier scale may be loose on main scale.
2. The jaws may not be at right angles to the main scale.
3. The graduations on scale may not be correct and clear.
4. Parallax may be there in taking observations.

SCREW GUAUGE

AIM:

To measure radius of a given wire using screw gauge.

Apparatus
Screw gauge, wire, half-metre scale and magnifying lens.

Formula:
 H.S.R=H.S.CXL.C

O.R=P.S.R+H.S.R

CR=OR-+ZC

Formula Expansion:

H.S.C-Head scale Coincidence in division.

P.S.R-Pitch scale reading in x10−2m.

L.C- Least count x10−2m.

C.R-Correct reading x10−2m.

O.R=Observed reading x10−2m.

Theory:
1. If with the wire between plane faces A and B, the edge of the cap lies ahead of Mb division
of linear scale.
Then, linear scale reading (L.S.R.) = N.
If nth division of circular scale lies over reference line.
Then, circular scale reading (C.S.R.) = n x (L.C.) (L.C. is least count of screw gauge) Total
reading (T.R.) = L.S.R. + C.S.R. = N+n x (L.C.).
2. D be the mean diameter and l be the mean length of the wire.

Principle:

The principle of a screw gauge is that the distance moved by the tip of a screw is directly
proportional to the number of rotations it makes when it's turned in a nut.

Procedure

1. Find the value of one linear scale division (L.S.D.).

2. Determine the pitch and the least count of the screw gauge and record it step wise.

3. Bring the plane face B in contact with plane face A and find the zero error. Do it three
times and record them. If there is no zero error, then record zero error nil.
 4. Move the face B away from face A. Place the wire lengthwise over face A and move
the face B towards face A using the ratchet head R. Stop when R turns (slips) without
moving the screw.

5. Note the number of divisions of the linear scale visible and uncovered by the edge of
the cap. The reading (IV) is called linear scale reading (L.S.R.).

6. Note the number (n) of the division of the circular scale lying over reference line.

7. Repeat steps 5 and 6 after rotating the wire by 90° for measuring diameter in a
perpendicular direction.

8. Repeat steps 4, 5, 6 and 7 for five different positions separated equally throughout the
length of the wire. Record the observations in each set in a tabular form.

9. Find total reading and apply zero correction in each case.

10. Take mean of different values of diameter.

11. Measure the length of the wire by stretching it along a half-metre scale. Keeping one
end of wire at a known mark, note the position of other end. Difference in position of
the two ends of the wire gives the length of the wire. Do it three times and record
them.

DIAGRAM:

Observations:

Least count= Zero Error: Zero correction:

S.NO Pitch scale Head scale H.S.R=HSCXLC OR=PSR+HSR CR=OR-
+
reading coincidence[HSC] ZC
[PSR]
unit x10−2m division x10−2m x10−2m x10−2m
Result
The radius of the given wire is………….

Precautions :

1. To avoid undue pressure; the screw should always be rotated by ratchet R and not by
cap K.

2. The screw should move freely without friction.

3. The zero correction, with proper sign should be noted very carefully and added
algebraically.

4. For same set of observations, the screw should be moved in the same direction to
avoid back-lash error of the screw.

5. At each place, the diameter of the wire should be measured in two perpendicular
directions and then the mean of the two be taken.

6. Readings should be taken at least for five different places equally spaced along the
whole length of the wire.

7. Error due to parallax should be avoided.

8. To avoid undue pressure; the screw should always be rotated by ratchet R and not by
cap K.
9. The screw should move freely without friction.
10. The zero correction, with proper sign should be noted very carefully and added
algebraically.
11. For same set of observations, the screw should be moved in the same direction to
avoid back-lash error of the screw.
12. At each place, the diameter of the wire should be measured in two perpendicular
directions and then the mean of the two be taken.
13. Readings should be taken at least for five different places equally spaced along the
whole length of the wire.
14. Error due to parallax should be avoided.