Q: The circular scale of a screw gauge has 200 divisions . When it is given 4 complete rotations , it moves through 2 mm . The least count of screw gauge is

(a) 0.25 x 10^{-2} cm

(b) 0.25 x 10^{-3} cm

(c) 0.001 cm

(d) 0.001 mm

Ans: (b)

Sol: $Pitch = \frac{2}{4} mm = 0.5 mm $

$\large L.C = \frac{Pitch}{200} = \frac{0.5}{200} mm $

Pitch = 0.25 x 10^{-2} mm

= 0.25 x 10^{-3} cm