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JEE Main · 2014 · 06 Apr 2014 · Offline · Units & Measurement

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A student measured the length of a rod and wrote it as 3.50 cm. Which instrument did he use to measure it?
  1. (A)A screw gauge having 100 divisions in the circular scale and pitch as 1 mm.
  2. (B)A screw gauge having 50 divisions in the circular scale and pitch as 1 mm.
  3. (C)A meter scale.
  4. (D)A vernier calliper where the 10 divisions in vernier scale matches with 9 division in main scale and main scale has 10 divisions in 1 cm.✓ Correct

Answer: (D)

Solution

The reading 3.50 cm is quoted to the nearest 0.01 cm, so the instrument's least count must be 0.01 cm. For the vernier described, one main-scale division is cm and ten vernier divisions cover nine main-scale divisions, so one vernier division is cm; the least count is cm, matching exactly. A metre scale reads only to cm, too coarse, while the two screw gauges read to mm and mm, far finer than the stated figure. The vernier calliper is the instrument that fits.

JEE Main · 2014 · 06 Apr 2014 · Offline · Single correct option

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