Q 11-01-188JEE MainJEE Main 2021 (26 Aug, Shift 1)Easy
In a Screw Gauge, fifth division of the circular scale coincides with the reference line when the ratchet is closed. There are $50$ divisions on the circular scale, and the main scale moves by $0.5$ mm on a complete rotation. For a particular observation the reading on the main scale is $5$ mm and the $20^{\text{th}}$ division of the circular scale coincides with reference line. Calculate the true reading.
Answer: (C) $5.15$ mm
Least count $= \dfrac{0.5}{50} = 0.01$ mm.
Zero error $= +5\times0.01 = +0.05$ mm.
Observed reading $= 5 + 20\times0.01 = 5.20$ mm.
True reading $= 5.20 - 0.05 = 5.15$ mm.
Solution by Sreeraj P, M.Sc Physics