The smallest unit on the sleeve of a micrometer screw gauge is 0.5mm. There are fifty divisions on the thimble…

Analyze the question: The smallest length a micrometer screw gauge can measure is its least count (also called its accuracy or resolution).

Concept: The pitch is the distance the screw advances in one full turn of the thimble. Here, the smallest unit on the sleeve is 0.5 mm, so the pitch is 0.5 mm.

Least count = Pitch ÷ Number of divisions on the thimble

Solution: Least count = 0.5 mm ÷ 50 = 0.01 mm

Now convert to cm, since the options are in cm: 0.01 mm = 0.01 ÷ 10 = 0.001 cm

Checking the other options:

• A (0.05 cm) = 0.5 mm, which is just the pitch, not the least count.
• B (0.01 cm) = 0.1 mm, which is wrong. It comes from forgetting to convert properly.
• C (0.005 cm) = 0.05 mm, which is wrong.
• E (0.0001 cm) = 0.001 mm, which is too small for this instrument.

Tip: Always keep track of the units. Many students compute 0.01 and pick B without noticing that 0.01 is in mm, while the options are in cm. Remember: to go from mm to cm, divide by 10.