Vernier Callipers Viva Questions – Measuring Diameter and depth
Vernier Callipers Viva Questions – Measuring Diameter and depth
Aim
(i) To measure the diameter of a given spherical body (e.g. a glass marble) using Vernier Callipers
(ii) To measure the internal diameter and depth of a given beaker using Vernier Callipers, and hence to determine its volume.
Basic Concepts
1. What is a vernier caliper?
An instrument used to measure lengths, diameters (internal and external), and depths accurately, up to 0.01 cm or 0.02 cm.
2. What is the principle of a vernier caliper?
It works on the principle that the difference between the values of one main scale division and one vernier scale division gives the least measurable value (vernier constant), allowing fractional parts of the smallest main scale division to be read accurately.
3. Name the parts of a vernier caliper.
Main scale, vernier scale, upper (internal) jaws, lower (external) jaws, depth probe/strip, and a screw (retainer) to fix the sliding jaw in position.
Vernier Constant (Least Count)
4. What is vernier constant (least count) of a vernier caliper?
The smallest length that can be measured accurately with it; V.C. = 1 M.S.D. − 1 V.S.D.
5. What is 1 M.S.D.?
The value of one smallest division on the main scale (usually 1 mm).
6. What is 1 V.S.D.?
The value of one division on the vernier scale, found by dividing the total length covered by n vernier divisions by n.
7. What is the alternate formula for vernier constant?
V.C. = Value of 1 main scale division / Total number of vernier scale divisions.
8. What is the usual value of vernier constant?
0.01 cm (when 1 M.S.D. = 1 mm and the vernier scale has 10 divisions equal to 9 main scale divisions).
9. If 1 M.S.D. = 1 mm and 10 V.S.D. = 9 M.S.D., what is the vernier constant?
1 V.S.D. = 0.9 mm; V.C. = 1 mm − 0.9 mm = 0.1 mm = 0.01 cm.
10. How can the vernier constant be reduced further?
By increasing the number of divisions on the vernier scale, so that each vernier division becomes closer in value to a main scale division.
11. Why do we need a vernier constant at all?
It tells us the smallest reliable reading the instrument can give, and hence the possible error in every measurement taken with it.
Zero Error
12. What is zero error in a vernier caliper?
The error that occurs when the zero of the vernier scale does not coincide with the zero of the main scale when the jaws are fully closed.
13. What are the types of zero error?
Positive zero error and negative zero error.
14. When is the zero error said to be positive?
When the zero of the vernier scale lies to the right of the zero of the main scale when the jaws are closed.
15. When is the zero error said to be negative?
When the zero of the vernier scale lies to the left of the zero of the main scale when the jaws are closed.
16. How is zero error corrected?
Corrected reading = Observed reading − Zero error (using the proper sign).
17. If zero error is −0.02 cm, is it added or subtracted from the observed reading?
Added (since correction = −Zero error, so we subtract −0.02 cm, i.e. add 0.02 cm).
18. Why must zero error be checked before every set of readings?
Because repeated use can wear the jaws slightly, and different instruments may have different zero errors, so it must be verified each time for accuracy.
Construction and Working
19. What are the lower (external) jaws used for?
To measure the external dimensions of an object, such as the diameter of a sphere, cylinder, or a rod.
20. What are the upper (internal) jaws used for?
To measure the internal dimensions of an object, such as the internal diameter of a hollow tube or a beaker.
21. What is the depth probe (strip/tail) used for?
To measure the depth of a hollow object such as a beaker, bottle, or cylinder.
22. What is the main scale?
The fixed scale (marked in cm and mm) on the body of the caliper, along which the vernier scale slides.
23. What is the vernier scale?
A small, movable auxiliary scale that slides along the main scale and helps read fractional parts of a main scale division.
24. What is the function of the screw (retainer) on a vernier caliper?
To lock the vernier scale in a fixed position after a measurement, so the reading can be noted without the jaws slipping.
Taking Readings
25. What is the Main Scale Reading (M.S.R.)?
The reading on the main scale just before (to the left of) the zero of the vernier scale.
26. What is the Vernier Scale Reading (V.S.R.)?
The number of the vernier division that exactly coincides with any division on the main scale.
27. What is the formula for the total (observed) reading?
Total Reading = M.S.R. + (V.S.R. × Vernier Constant).
28. Why do we look for the vernier division that “exactly” coincides with a main scale division?
Because that coinciding division tells us precisely how much extra length beyond the M.S.R. is present, which is the basis of the vernier’s precision.
29. Why do we take multiple readings at different points/orientations of the object?
Because the object may not have a perfectly uniform shape, so several readings give a more accurate and reliable average value.
Precautions and Errors
30. Why should parallax error be avoided while reading a vernier caliper?
Because viewing the scale at an angle instead of directly from the front can make the coinciding division appear different from the actual one, causing an error.
31. What precautions should be taken while using a vernier caliper?
Handle it gently, check zero error before use, do not apply excessive force on the jaws, avoid parallax, and keep it clean, dry, and rust-free.
32. Why shouldn’t excessive force be applied while closing the jaws on an object?
It can compress soft objects or damage the jaws/screw, leading to an inaccurate reading and wear on the instrument.
33. What error can occur due to worn-out or loose jaws?
Readings become inconsistent or systematically incorrect, since the jaws no longer close perfectly, effectively introducing an additional zero error.
34. Why should the object be held perpendicular to the jaws while measuring?
A tilted object gives a reading larger than the actual dimension, since the caliper would be measuring a slant length instead of the true one.
Applications and Comparisons
35. What are the uses of a vernier caliper?
Measuring external length/diameter, internal diameter, and depth of objects like spheres, cylinders, tubes, beakers, and coins.
36. How is the internal diameter of a tube measured using a vernier caliper?
By inserting the upper (internal) jaws into the tube, opening them till they touch the inner walls, and taking the reading — sometimes adding the jaw thickness if the instrument requires it.
37. How is depth measured using a vernier caliper?
By resting the caliper’s main body on the rim of the object and lowering the depth probe/strip until it touches the bottom, then taking the reading.
38. What is the typical range of a laboratory vernier caliper?
0 to 15 cm (or 0 to 20 cm), though this varies by instrument.
Numerical/Conceptual
39. If M.S.R. = 2.3 cm, V.S.R. = 4, and V.C. = 0.01 cm, what is the observed reading?
Observed Reading = 2.3 + (4 × 0.01) = 2.34 cm.
40. If zero error is +0.02 cm and observed reading is 3.45 cm, find the corrected reading.
Corrected Reading = 3.45 − 0.02 = 3.43 cm.
41. Why is it important to note the vernier constant before starting the experiment?
Because every subsequent calculated reading depends on it, and it tells us the maximum precision (and hence possible error) of our final result.
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