Question

The thimble of a screw gauge has 50 divisions for one rotation. The spindle advances 1 mm when the screw is turned through two rotations.

1. What is the pitch of the screw?
2. What is the least count of screw gauge?
3. When the screw gauge is used to measure the diameter of wire the reading on the sleeve is found to be 0.5 mm and reading on thimble is found, 27 divisions. What is the diameter of the wire in centimetres?

Answer 1

Pitch of screw gauge is the distance moved by spindle in one revolution = 1/2 = 0.5 mm

(1) ∴ Pitch = 0.5 mm OR 0.05 cm

(2) The thimble of a screw gauge has 50 divisions for one rotation.
⇒ No. of circular scale divisions = 50

Least count (L.C.) = `"Pitch"/"No. of circular scale divisions"`

= `0.05/50` cm

= 0.001 cm

(3) Main scale reading = 0.5 mm = 0.05 cm
Circular scale reading = 27 div.
Diameter of wire = M.S. reading + L.C. × C.S. reading
= 0.05 + 0.001 × 27
= 0.05 + 0.027
Diameter of wire = 0.077 cm