Question

In an experiment, the angles are required to be measured using an instrument. $29$ divisions of the main scale exactly coincide with the $30$ divisions of the vernier scale. If the smallest division of the main scale is half -a-degree $(0.5^?)$, then the least count of the instrument is

• A. half minute
• B. one degree
• C. half degree
• D. one minute

Answer 1

Answer: (D)

one minute

Answer 2

$29$ divisions of main scale coincide with $30$ divisions of vernier scale. Hence, one division of vernier scale $=\frac{30-29}{30}$ of main scale $=\frac{1}{30}\times0.5^{?}$ $=\frac{1}{30}\times0.5\times60\,min$ $=1\,min$