Question

A micrometer is made using a bar having 20 threads per cm. On its circular scale it has 100 divisions. A student reads 5 divisions after 1 cm mark on linear scale and 37 division of circular scale, coinciding with mainscale for the diameter of a cylinder. Write the diameter.

• A. 1.2537 cm
• B. 1.2685 cm
• C. 1.2537 ± 0.0005 cm
• D. 1.2685 ± 0.0005 cm

Answer 1

Answer: (D)

1.2685 ± 0.0005 cm

Answer 2

d = pitch × (number of divisions on linear scale) + least count (number of circular scale divisions coinciding with linear scale)

= $\frac { 1 } { 20 }$ (25) + $\frac { 1 } { 20 \times 100 }$ × 37 = 1.2685

d = 1.2685 ± 0.0005 cm