The least count of the main scale of a vernier callipers is $1 \mathrm{~mm}$. Its vernier scale is divided into 10 divisions and coincide with 9 divisions of the main scale. When jaws are touching each other, the $7^{\text {th }}$ 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 betwen $3.1 \mathrm{~cm}$ and $3.2 \mathrm{~cm}$ and $4^{\text {th }}$ VSD coincides with a main scale division. The length of the cylinder is : (VSD is vernier scale division)
Correct Option: 3
(3) L.C. of vernier callipers $=1 \mathrm{MSD}-1 \mathrm{VSD}$
$=\left(1-\frac{9}{10}\right) \times 1=0.1 \mathrm{~mm}=0.01 \mathrm{~cm}$
Here $7^{\text {th }}$ 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.
Zero error $=7 \times 0.1=0.7 \mathrm{~mm}=0.07 \mathrm{~cm}$
Length of the cylinder $=$ measured value $-$ zero error $=(3.1+4 \times 0.01)-0.07=3.07 \mathrm{~cm}$.
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