Question

In an experiment the angles are required to be measured using an instrument. In this 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 degree $(={0.5}^o)$, 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

30 divisions of vernier scale coincide with 29 divisions of main scale.
$\therefore 1V.S.D=\frac{29}{30}M.S.D$

Least count$=1MSD-1VSD$

$=1MSD-\frac{29}{30}MSD$

$=\frac{1}{30}MSD=\frac{1}{30}\times {0.5}^o$

$=\frac{1}{30}\times 30min=1min$