In a complete rotation, spindle of a screw gauge advances by `(1)/(2)mm`. There are `50` divisions on circular scale. The main scale has `(1)/(2)mm` marks to (is graduated to `(1)/(2)mm`)
If a wire is put between the jaws, `3` main scale divisions are clearly visible, and `20th` division of circular scale coincides with reference line. Find diameter of wire in correct significant figures.

Options

A. 1.7 mm
B. 1.70 mm
C. 1.58mm
D. 1.30 mm

Answer

B

Explanation

Reading `3 xx 1/2 + 20 xx "Least count"`
least count = `("pitch")/("Number of division") = ((1)/(2))/(50) mm = 0.01 mm`
So, reading = `1.5 + 20 xx .01 = 1.70 mm`.