Question

The main scale of a vernier callipers reads 10 mm in 10 divisions. 10 divisions of Vernier scale coincide with 9 divisions of the main scale. When the two jaws of the callipers touch each other, the fifth division of the vernier coincides with some main scale divisions and the zero of the vernier is to the right of zero of main scale. When a sphere is tightly placed between the two jaws, the zero of vernier scale lies slightly behind 3.2 cm and the fourth vernier division coincides with a main scale division. The diameter of the sphere is :

(1) 2.07 cm

(2) 3.09 cm

(3) 4.05 cm

(4) 5.03 cm

Answer 1

Correct option is (2) 3.09 cm

Zero error = 0.5 mm = 0.05 cm.

Observed reading of sphere diameter = 3.1 cm + (4) (0.01 cm) = 3.14 cm

Actual thickness of sphere = (3.14) - (0.05) = 3.09 cm