Question

Fig., below shows the reading obtained while measuring the diameter of a wire with a screw gauge. The screw advances by 1 division on the main scale when circular head is rotated once.  

Find:
(i) Pitch of the screw gauge,
(ii) Least count of the screw gauge and
(iii) The diameter of the wire.

Answer 1

No. of divisions on the circular scale = 50

(i) Pitch = Distance moved ahead in one revolution

 = 1 mm/1 = 1 mm.

(ii) L.C. = Pitch/No. of divisions on the circular head

 = (1/50) mm

 = 0.02 mm

(iii) Main scale reading = 4 mm

No. of circular division coinciding with m.s.d. (p) = 47

Circular scale reading = p × L.C.

 = (47 × 0.02) mm

 = 0.94 mm

Diameter (Total reading) = M.s.r. + circular scale reading

 = (4 + 0.94) mm

   = 4.94 mm