Two full turns of the circular scale of a screw gauge cover a distance of 1 mm on its main scale. The total number of divisions on the circular scale is 50. Further, it is found that the screw gauge has a zero error of -0.03 mm while measuring the diameter of a thin wire, a student notes the main scale reading of 3 mm and the number of circular scale divisions in line with the main scale as 35. The diameter of the wire is
- (A)3.32 mm
- (B)3.73 mm
- (C)3.67 mm
- (D)3.38 mm✓ Correct
Answer: (D)
Solution
Two full rotations advance the screw by , so the pitch is per turn, and dividing by the circular divisions gives a least count of . The raw reading is the main-scale plus , i.e. . The zero error is , and a negative zero error is corrected by adding its magnitude, so the true diameter is .
JEE Main · 2008 · 27 Apr 2008 · Offline · Single correct option