Q 11-01-179JEE MainJEE Main 2021 (25 Feb, Shift 1)Medium
The pitch of the screw gauge is 1 mm and there are 100 divisions on the circular scale. When nothing is put in between the jaws, the zero of the circular scale lies 8 divisions below the reference line. When a wire is placed between the jaws, the first linear scale division is clearly visible while 72nd division on circular scale coincides with the reference line. The radius of the wire is
Answer: (B) 0.82 mm
Least count $= \dfrac{1\ \text{mm}}{100} = 0.01$ mm.
With the circular-scale zero 8 divisions below the reference line, the zero error is $+8\times0.01 = +0.08$ mm.
Observed reading $= 1 + 72\times0.01 = 1.72$ mm. Corrected diameter $= 1.72 - 0.08 = 1.64$ mm, so the radius is $0.82$ mm.
Solution by Sreeraj P, M.Sc Physics