Question

If the screw on a screw-gauge is given six rotations, it moves by 3 mm on the main scale. If there are 50 divisions on the circular scale the least count of the screw gauge is :

(1) 0.001 mm

(2) 0.001 cm

(3) 0.02 mm

(4) 0.01 cm

Answer 1

Answer is (2) 0.001 cm

Given on six rotation, reading of main scale changes by 3mm. 

∴ 1 rotation corresponds to (1/2) mm 

Also no. of division on circular scale = 50. 

∴ Least count of the screw gauge will be

(0.5/50) mm = 0.001 cm.

Answer 2

Answer is (2) 0.001 cm

Pitch = 3/6 = 0.5 mm

L.C. = 0.5mm/50 = (1/100) mm

= 0.01 mm = 0.001 cm