Q.

The main scale of a vernier callipers has n divisions/cm. n divisions of the vernier scale coincide with (n-1) divisions of main scale. The least count of the vernier callipers is  [2019]

1 1(n+1)(n-1)cm  
2 1ncm  
3 1n2cm  
4 1n(n+1)cm  

Ans.

(3)

If n divisions of the vernier scale coincide with (n−1) divisions of the main scale:

Therefore, nVSD=(n-1)MSD1VSD=(n-1)nMSD

Least count= 1MSD-1VSD=1MSD-(n-1)nMSD =1MSD-1MSD+1nMSD=1nMSD
1n×1n=1n2cm     1MSD=1ncm