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Question: Answered & Verified by Expert
A vernier calipers has $1 \mathrm{~mm}$ marks on the main scale. It has 20 equal divisions on the vernier scale which match with 16 main scale divisions. For this vernier calipers, the least count is
PhysicsExperimental PhysicsJEE AdvancedJEE Advanced 2010 (Paper 2)
Options:
  • A
    $0.02 \mathrm{~mm}$
  • B
    $0.05 \mathrm{~mm}$
  • C
    $0.1 \mathrm{~mm}$
  • D
    $0.2 \mathrm{~mm}$
Solution:
2990 Upvotes Verified Answer
The correct answer is:
$0.2 \mathrm{~mm}$
Least count of vernier calipers
$$
\begin{aligned}
& \text { LC }=1 \mathrm{MSD}-1 \text { VSD } \\
& =\frac{\text { Smallest division on main scale }}{\text { Number of divisions on vernier scale }} \\
& 20 \text { divisions of vernier scale } \\
& =16 \text { divisions of main scale } \\
& \therefore \quad 1 \mathrm{VSD}=\frac{16}{20} \mathrm{~mm}=0.8 \mathrm{~mm} \\
& \therefore \quad \text { LC }=1 \mathrm{MSD}-1 \mathrm{VSD} \\
& =1 \mathrm{~mm}-0.8 \mathrm{~mm} \\
& \therefore \quad=0.2 \mathrm{~mm} \\
&
\end{aligned}
$$
$\therefore$ The correct option is (d).

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