The least count of the main scale of a vernier callipers is 1 mm. Its… | JEE Main 2020 (2 Sep, Shift 1)

Q53JEE Main 2020 · 2 SEP · SHIFT 1Difficult

Least Count, Vernier Callipers & Screw Gauge

The least count of the main scale of a vernier callipers is 1 mm. Its vernier scale is divided into 10 divisions and coincide with 9 divisions of the main scale. When jaws are touching each other, the 7th division of vernier scale coincides with a division of main scale and the zero of vernier scale is lying right side of the zero of main scale. When this vernier is used to measure length of a cylinder the zero of the vernier scale between 3.1 cm and 3.2 cm and 4th VSD coincides with a main scale division. The length of the cylinder is: (VSD is vernier scale division)

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Answer: (c)

LC $= 1 - 0.9 = 0.1\text{ mm} = 0.01\text{ cm}$
Vernier zero right of main zero: zero error $= +7\times 0.01 = +0.07\text{ cm}$
Observed reading $= 3.1 + 4\times 0.01 = 3.14\text{ cm}$
Length $= 3.14 - 0.07 = 3.07\text{ cm}$ . So the answer is (c).

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Least Count, Vernier Callipers & Screw Gauge question from JEE Main 2020 (2 Sep, Shift 1)

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