Q86 / 90 · JEE Main 2009 · Physics

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 $\left(=0.5^{\circ}\right)$, then the least count of the instrument is

  • Correct answer
    A
    one minute
  • B
    half minute
  • C
    one degree
  • D
    half degree

Solution

$$ \text { Least count }=\frac{\text { value of main scale division }}{\text { No of divisions on vernier scale }}=\frac{1}{30} \mathrm{MSD}=\frac{1}{30} \times \frac{1}{2}^{\circ}=\frac{1}{60}^{\circ}=1 \text { minute } $$

Hence, the correct answer is option: 'A'.

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