An angle measuring instrument reading up to one-sixth of a degree on the main scale is equipped with a Vernier having 19 main scale divisions divided into 20 parts. The correct least count of the instrument is
- A60 seconds
- B30 secondsCorrect
- C20 seconds
- D10 seconds
Solution
Concept
Least count of a vernier
Formula
Least count = (value of one main scale division) / (number of vernier divisions)
Step-by-step solution
1. One main scale division = 1/6° = 10′ = 600″. 2. Vernier has 20 divisions equal to 19 main scale divisions. 3. Least count = 600″ / 20 = 30″.
Explanation
Least count = smallest main scale division divided by the number of vernier divisions: 10′ ÷ 20 = 0.5′ = 30″.
Shortcut
LC = S ÷ n.
Common mistake
Dividing by 19 instead of 20.
Correct answer: B) 30 seconds