Question

The main scale of a vernier callipers reads 10 mm in 10 divisions of Vernier scale coincide with 9 divisions of the main scale. When a cylinder is tightly placed between the two jaws, the zero of vernier scale lies slightly behind 3.2 cm and the fourth vernier division coincides with a main scale division. The diameter of the cylinder is :

• A. 3.09 cm
• B. 3.14 cm
• C. 3.04 cm
• D. 3.03 cm

Answer 1

The correct option is B 3.14 cm

Vernier constant $=\frac{1}{N}S=\frac{1}{10}=0.1mm$

The instrument has a positive error which is $e=NC=7\times 0.1mm=0.07cm$

Vernier scale reading $==4\times 0.01=0.04cm$ $($since the fourth vernier division with a scale division$)$

therefore$,$ he observed reading $3.1+004=3.14cm.$

Hence,

option $\left(B\right)$ is correct answer.