A brilliant student of Class `XII` constructed a vernier calipers as shown. He used two identical inclines of inclination `37^(@)` and tried to measure the length of line `AB`. The length of line `AB` is
.

Options

A. `(21)/(4)`mm
B. `(25)/(4)` mm
C. `(18)/(4)` mm
D. None of these

Answer

B

Explanation

Least count `=(l)/(cos theta)-l=1((1)/(4//5)-1)=((5)/(4)-1)=(1)/(4)`mm
Length `AB=(4)((l)/(cos theta))+(5)((l)/(cos theta)-l)=4((5)/(4))+5((1)/(4))=5+(5)/(4)=(25)/(4)`mm.