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A travelling microscope has a main scale with least count of 0.5 mm. On the vernier scale, 50 divisions coincide with 49 main scale divisions. If the main scale reading is 7.45 cm and the 29th vernier division coincides with a main scale line, what is the complete reading?

1. 7.459 cm
2. 7.453 cm
3. 7.479 cm
4. 7.48 cm

Correct answer: 7.479 cm

Solution

The vernier least count is 0.5 mm / 50 = 0.01 mm = 0.001 cm. With 29th vernier division coinciding, vernier reading = 29 x 0.001 cm = 0.029 cm. Total = 7.45 + 0.029 = 7.479 cm.

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