How Vernier Caliper actually measures the length?
Let us suppose we are having a small rod and cm scale as
shown:
If we ask you what is the length of the rod you would say it
is somewhere between 2.1 cm and 2.2 cm and for general practical purpose we
would treat it to be 2.2 cm, as it seems somewhat closer to 2.2 cm.
Here the smallest measurement which can be made is 0.1 cm, this is nothing but the Least Count (L.C.) of this centimeter scale. So we here infer that if our object lies between two successive markings as in above case, we won’t be able to correctly define its length.
When we deal with experiments where accuracy up to 2nd decimal(as in cm) is required, using this normal scale won’t be a great idea! This is where Vernier Caliper comes into the picture. This length measuring instrument was invented by Pierre Vernier the French Mathematician in 1631.
The regular vernier caliper allow us to find length up to 2nd
decimal (as in cm) without actually need to magnify the scale. This caliper
uses another scale called ‘vernier scale’ along with regular scale to get
higher precise and accurate readings.
1. Outside
large jaws: used to measure external diameter of an object (like a hollow
cylinder) or width of an object (like a rod), diameter of an object (like a
sphere)
2. Inside
small jaws: used to measure internal diameter of an object (like a hollow
cylinder or pipe)
3. Depth
probe/rod: used to measure depths of an object (like a small beaker) or a
hole
4. Main
scale (Metric): scale marked every mm and helps to measure length correct
up to 1 mm
5. Main
scale (Imperial): scale marked in inches and fractions
6. Vernier
scale (Metric) gives interpolated measurements to 0.1 mm or
better
7. Vernier
scale (Imperial) gives interpolated measurements in fractions of an
inch
8. Retainer:
used to block movable part to allow the easy transferring of a measurement
The portion between two successive markings is called as 1 Division.
Here in our case MS having 1 division of length 1mm (or 0.1cm). We would
call it as 1 MSD = 1 mm.
Similarly we would define a Vernier Scale Division i.e. 1
VSD in a following way,
In most of the cases we use regular Vernier Caliper which
has 10 VSD = 9 MSD.
This result gives us
1 VSD = 0.9 MSD
1 VSD = 0.9 x (1 mm) or
1 VSD = 0.9 mm
In case of Vernier Caliper we define Least count(LC) as,
LC
= 1 MSD – 1 VSD
So in our regular Vernier Caliper LC = 1 mm – 0.9 mm
LC = 0.1 mm
Let us suppose we are having a rod AB as shown in below
figure:
Procedure to measure length of a rod:
1) Hold
the given object between two outside large jaws of the vernier calliper. Make
sure you are not tightening it too much.
2) Then
see division on main scale just before the 0 of Vernier scale, this would give
us the Main Scale Reading (MSR).
In the above
diagram 24th division of MS is just before the 0 of VS.
Therefore, MSR=
MSD * 1 mm
=
24 * 1 mm
MSR= 24 mm
3) Now the division on Vernier scale which exactly coincides
with the Main Scale Divisions is called as VSD. Then the Vernier Scale Reading
can be defined by the following way
We
define VSR = LC * (VSD coinciding with that of MSD)
Here 8th
Division on Vernier Scale Coincides with one of the divisions of the Main Scale.
Thus, VSR = 0.1 mm * ( 8)
VSR = 0.8 mm
Let us suppose we are having a rod AB as shown in below
figure:
Procedure to measure length of a rod:
Now Total Reading(TR) is sum of MSR and VSR
Therefore, TR =
MSR + VSR
TR = 24 mm + 0.8 mm
TR = 24.8 mm
5) So finally we got the length of the rod as 24.8 mm (2.48 cm)
You might be wondering about why we took VSR = LC * (VSD coinciding with that of MSD)
In that case let’s take a closure look at the Vernier
Caliper once again and you would find answer to your question:
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