Class 11 Physics practical reading To measure the diameter of a small spherical or cylindrical body using a vernier calliper.

Aim

To measure the diameter of a small spherical or cylindrical body using a vernier callipers.

Apparatus Required

A vernier callipers, a small spherical (e.g. a bob) or a small cylindrical body.

Theory

Vernier callipers consists of four main parts : (i) Vernier scale (ii) Main scale (iv) Metallic strips (iii) Movable jaws

When a body is held between the jaws of a vernier callipers, let zero of vernier scale lies ahead of Nth division of main scale. 

The main scale reading (M.S.R.) = N (in cm) and of nth division of vernier scale coincides with any of main scale division then vernier scale reading = n x V.C. (cm). 

Here vernier constant (V.C.) = 1 M.S.D. - 1 V.S.D. 

Total reading = M.S.R. + V.S.R. T.R. = [N + (n x V.C.)] cm 

Procedure

(i) Read the main scale and find the value of one main scale division (M.S.D). Also calculate the vernier constant using V.C. =1 M.S.D. 1 V.S.D.
(ii) Find the zero error, if any, positive or negative and record it. 

(iii) Hold the given solid body between jaws A and B, ensure that the body is held between the jaws without any undue pressure. Fig.

Vernier callipers to measure diameter of a sphere.

(iv) Note the main scale reading N to the left of zero mark of the vernier scale. Record it. 

(v) Note the number of vernier scale divisions (n) coinciding with any of the main scale division and record it Total Reading = [N + (n x V.C.)] cm. 

(vi) Turn the given body through 90° and again note N' and n' and hence T.R. is T.R. = [N' + (n' x V.C.)]. This complete one set of observation. 

(vii) Repeat the above steps (iii) to (vi) at two different positions of the given body. 

(viii) Calculate the mean corrected diameter.

Observations

Precautions

1. The movement of vernier scale on the main scale should be smooth. If not, oil it and clean the vernier callipers. 

2. The body should be gripped firmly between the jaws. 

3. Vernier constant and zero error should be carrefully calculated and recorded. 

4. Observations should be taken at right angles at one place. 

5. Use the magnifying lens to find the number of coinciding vernier divisions.

Sources of Error

1. Some errors may be creep due to parallex. 

2. The jaws may not be at exactly right angles to the main scale.