A vernier callipers is designed by dividing 19 M.S.D into 20 V.S.D & value of 1
M.S.D=1mm. When two jaws are kept in contact, zero of vernier is right of zero of
mains scale & 12th vernier division is coinciding with one of main scale division. If
this vernier callipers is used to find the length of the object, it is observed that zero of
vernier lies between 10 & 11th M.S.D & 10th vernier division is coinciding with one of
the main scale division. Then find length of cylinder ?
Answers
Explanation:
How much we know about the Vernier calipers?
Measurement is a fundamental part of all scientific experiments, including Physics. At one extreme, our vast universe extends this measuring exercise to light-years, the distances so vast that we cannot see them from our eyes. On the other extreme of the smallest distances, new discoveries are pushing it down to femto-meter (10-15 m) or even less. These distances are so small that we cannot see them from our eyes. At every 1-2 order of magnitude change in distance, our instruments to measure the distances accurately can differ. When the distances, we want to measure, are in the range of 10-2 mm to 1 mm, we use Vernier Calipers and Screw Gauge for precise measurement. In this article, we are going to focus on these measuring instruments only.
In class 11th Physics lab, we were trained to answer the following questions:
How to find the Least Count (LC) or Vernier Constant?
How to read Main Scale Reading (MSR) and Vernier Scale Reading (VSR)?
How to find the zero error?
How to use the above data to get the final measurement?
Answers to these how to questions kept us content for 22 years. But this was not adequate to solve the IIT JEE 2016 problem. We needed to figure out some more interesting why questions like:
Why least count is the ratio of "value of 1 Main Scale Division" to the "Total number of divisions on the vernier scale".
Why the measured value is given by: Observed Value = MSR + LC×VSR.
Why the zero error is subtracted from the observed value i.e., True Value = Measured Value - Zero Error.
Let us start our journey with a Vernier calipers without zero error. When two jaws are closed, 0th mark on the Vernier scale is aligned with the 0th mark on the main scale as shown in the figure 1. Also note that 10th mark on Vernier scale coincides with the 9th mark on main scale.
One main scale division (MSD) is the distance between two successive marks on the main scale. It is given in the figure 1 that 1 MSD is equal to 1 mm. One Vernier scale division (VSD) is the distance between two successive marks on the Vernier scale. It is given that 10 VSD = 9 MSD. Thus, 1 VSD = (9/10) MSD = 0.9 mm i.e., distance between two successive marks on the Vernier scale is 0.9 mm.