Vernier caliper is an instrument used to measure the length, diameter, radius etc. It can measure up to 1/10 of mm (or 0.1 mm 0.01 cm) which is called at least count of V.C.It is used by the lathe mechanic for making metallic cylinders of different sizes.
There are two scales of V.C
- Vernier scale
- Main scale
The main scale is graduated is centimeter while Vernier scale slides along the main scale and is graduated in division (less than the millimeter).
Parts and function of vernier caliper
There are two sets of jaws:
- Two jaws
- Main scale
- vernier scale
(1) Lower Jaws:
The lower jaws A and B are used to measure length. The thickness or external diameter of an object.
The upper jaws C and D are used to measure the internal diameter of objects like a hollow cylinder or tube.
The jaws A and B are fixed where B and D are moveable. The movable jaws are attached to the vernier and they slide along the main scale.
- The smallest reading which can be accurately measured with a vernier caliper is called its least count (L.C),it is also known as vernier constant. It is the difference between one main scale division which is 1 mm and one vernier division which is (0.9) .
L.C = 1 mm – 0.9 mm =0.1 mm
There is another method to find least count which is given as:
Vernier caliper zero error
When the jaws of Vernier calipers are brought into contact, the zero of the Vernier must coincide with the zero of the main scale. Otherwise, the instrument has an error called zero error. Zero error can be negative or positive.
Negative Zero Error
If the zero of the Vernier scale is to the left of the zero of the main scale then the error is negative. Since the zero error is negative, the zero correction will be positive.
Positive zero error
If the zero of the Vernier scale is to the right of the zero of the main scale then the error is positive. Since the zero error is positive, the zero correction will be negative.
How to read a vernier caliper?
We can learn about the use of V.C with the help of an example by measuring the area of the cross-section of a solid cylinder by measuring its diameter with Vernier caliper. We will solve this example step by step.
- Find the least count. Close the jaws to check the Zero error and calculate the zero correction.
- Hold the cylinder between the two jaws of the vernier calliper . Tighten the jaws gently .
- Note the main scale division which is either coinciding or is on the left of vernier scale zero.
- Record this value as main scale reading (M).
- Note the vernier division (n) which exactly coincides with any one division of the main scale.
- Multiply this “n” with least count and calculate the value of fraction (x) which is to be added in the main scale reading.
X = ( n × LC )
- Add the values ‘M ‘ and ‘X ‘ to observed value (Y) of diameter.
Y = M + X
- Apply zero correction to obtain correct diameter.(D)
D = Y ± Z C
- Take at least two readings by inserting the cylinder cross-section wise between the jaws and get the average diameter.
- Calculate the radius of the cylinder
Observations and Data
Least count (LC) = 0.1 mm = 0.01 cm
Suppose zero error is = 0.7 cm which is positive error so:
Zero correction ( ZC ) = -0.07 cm
|No of Obs||
Main scale reading
No of vernier divisions
coinciding with the main scale divisions ( n)
Fraction to be added
X=n × LC
D=Y ± ZC
|1||2.2 cm||6||6 × 0.01=0.06 cm||2.2 + 0.06=2.26 cm||2.26 -0.07=2.19 cm|
|2||2.3 cm||6||6 × 0.01=0.06 cm||2.3+0.06=2.36 cm||2.36 -0.07=2.29 cm|
|3||2.4 cm||6||6 ×0.01=0.06 cm||2.4+0.06=2.46 cm||2.46 -0.07=2.39 cm|
Mean diameter (D) = 2.29 cm
Radius of the cylinder (r ) = D/2 = 2.29 /2 = 1.145 cm
Area of cross section of solid cylinder = π r²
=3.14 (1.145)² cm²
Area of cross section of solid cylinder will be =4.11 cm²
Cautions about use of V caliper
- Jaws of V C should be closed gently
- Zero correction should be applied
- Both jaws should touch the cylinder
Uses of vernier caliper
- It is used to find diameter internally and also externally.
- Plumbers,aluminium and steel window makers also use it.
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