Why is the beam of a vernier caliper made long and rigid during construction?
To support long measurement range without bending
In a vernier caliper the beam is the long central bar that carries the fixed jaw and the graduated main scale, and along which the movable jaw slides. Its mechanical duty is to act as the load-bearing backbone of the whole instrument.
When the jaws grip a workpiece, a gripping force is applied at the jaw tips, which are set well away from the beam axis. This force tends to bend the beam.
Any bending of the beam would swing the jaws out of parallel and shift the movable jaw relative to the scale, so the reading would no longer represent the true size.
To measure large workpieces the jaws must be separated by a long distance, which means the beam must span that full range while still resisting the bending force acting over that length.
The beam is therefore made long enough to cover the required measuring range and stiff (rigid) enough that it does not deflect under the gripping load, keeping the jaws square and the reading true.
Providing a smooth guide (option 1) and a stable reference surface (option 2) are useful side benefits of a straight beam, but they are not the reason it is made long; they do not explain the length.
Rigidity does not change the least count (option 3), since least count depends only on the vernier graduations, not on beam stiffness.
Hence, the answer is To support long measurement range without bending.
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Important Questions from Caliper
How many divisions are graduated on the thimble of micrometer?
The least count of Vernier bevel protractor is ____
In a Vernier calliper, 39 main scale divisions are divided into 40 equal points on the Vernier scale. Then what is its least count (LC) in mm? (Take the value of main scale division = 1mm).
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