The distance moved by the screw of a screw gauge is 2 mm in four rotations and there are 50 division

Question

The distance moved by the screw of a screw gauge is 2 mm in four rotations and there are 50 divisions on its cap. When nothing is put between its jaws, $30^{	ext {th }}$ division of circular scale coincides with the reference line, with zero of circular scale lying above the reference line. When a plate is placed between the jaws, the main scale reads 2 divisions and the circular scale reads 20 divisions. The thickness of the plate is.....

Professor PC Thomas Classes · Answer

$\begin{aligned} & L \cdot C=\frac{	ext { Pitch }}{N}=\frac{0.5 \mathrm{~mm}}{50}=0.01 \mathrm{~mm} \ & 	ext { zero error }=M S R+C S R \ & =-1 	imes 0.5+30 	imes 0.01 \ & =-0.20 \mathrm{~mm} \ & 	ext { Reading }=2 	imes 0.5+20 	imes 0.01 \ & =1.20 \mathrm{~mm} \ & 	ext { thickness }=	ext { Reading - zero error } \ & =1.20-(-0.20) \ & =1.40 \mathrm{~mm}\end{aligned}$