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If the screw of a screw-gauge is given six rotations, it moves 3 mm on the main scale. If there are 50 divisions on the circular scale, the least count of the screw gauge is

Asked in JEE Main 9th Jan 1st Shift 2020 · Pitch and least count

• (1) 0.001 cm
• (2) 0.01 cm
• (3) 0.02 mm
• (4) 0.001 mm

Step-by-step solution

Why the other options are wrong

• (2) Correct number, wrong unit: 0.01 mm=0.001 cm, not 0.01 cm.
• (3) Takes the pitch as 1 mm instead of 0.5 mm.
• (4) Off by a factor of ten: 0.01 mm mis-written as 0.001 mm.

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