Using venier calipers, which of the following readings gives the correct measurement for the length of a rod?

Analyze the question

The question asks which reading is a valid measurement from a vernier caliper. The key is the precision (least count) of the instrument.

Concept

A standard vernier caliper has:

• Main scale divisions of 1 mm (0.1 cm)
• A vernier scale with 10 divisions, giving a least count of 0.1 mm = 0.01 cm

So a reading from a vernier caliper is recorded to two decimal places in centimetres (the nearest 0.01 cm).

Reading = main scale reading + (vernier division coinciding × 0.01 cm)

Solution

Check each option:

• A. 4.1 cm – only one decimal place. This is the precision of a plain ruler (nearest mm), not a vernier caliper. It doesn't show the vernier contribution.
• B. 4.13 cm – two decimal places (main scale 4.1 cm + vernier 3 × 0.01 cm). This matches the precision of a vernier caliper. ✔
• C. 125 cm – no decimal places, and far too long. Vernier calipers measure small lengths (typically up to about 15 cm). ✘
• D. 1254 cm – about 12.5 m, impossible for a vernier caliper and has no decimal precision. ✘

Answer

The correct option is B (4.13 cm).

Tip

For vernier calipers, remember: cm readings with 2 decimal places (or mm readings with 1 decimal place). For a micrometer screw gauge, the reading is usually in mm with 2 decimal places (e.g., 4.13 mm). Always check the least count first and make sure your answer matches that precision.