When both jaws of vernier callipers touch each other, zero mark of the vernier scale is right to zero mark of main scale, 4ᵗʰ mark on vernier scale coincides with certain mark on the main scale. While measuring the length of a cylinder, observer observes 15 divisions on main scale and 5ᵗʰ division of vernier scale coincides with a main scale division. Measured length of cylinder is ____ mm.
(Least count of Vernier calliper =0.1 mm )

Solution

Physics sir · 3 steps

Take the reading first, then fix it. The zero error is positive here, so subtract it.

1. Find zero error. With the jaws closed, the vernier zero sits to the right of the main scale zero. That is a positive zero error, and its size is 4 × 0.1 = +0.4 mm.
2. Observed reading. The main scale reads 15 divisions, which is 15 mm. The 5th vernier division coincides, which adds 5 × 0.1 = 0.5 mm. The observed reading is 15.5 mm.

   True length = Observed reading - Zero error = 15.5 - 0.4

3. So. The measured length of the cylinder is 15.1 mm, which is option (d).

The idea to keep. Vernier zero to the right of the main zero means the instrument already reads too much, so the zero error is positive and you subtract it. To the left means negative, so you add.

Answer from the NTA final answer key. Solution by PrepWiser.