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

Options

A. 3.2 cm
B. 3.21 cm
C. 3.07 cm
D. 2.99 cm

Answer

C

Explanation

Least count of Vernier callipers `= (1 -9/10)xx1` mm
= 0.1 mm
`:.` Zero error `=7xx0.1=0.7` mm
Measured value = `(31+4xx0.1)` mm
= 31.4mm
`:.` Length of cylinder = 31.4 - 0.7
= 30.7mm
= 3.07 cm.