# Using a Micrometer(Edexcel International A Level Physics)

Author

Katie M

Expertise

Physics

## Using a Micrometer

• A micrometer, or a micrometer screw gauge, is a tool used for measuring small widths, thicknesses or diameters
• For example, the diameter of a copper wire

• It has a resolution of 0.01 mm
• The micrometer is made up of two scales:
• The main scale - this is on the sleeve (sometimes called the barrel)
• The thimble scale - this is a rotating scale on the thimble

Components of a micrometer

• The spindle and anvil are clamped around the object being measured by rotating the ratchet
• This should be tight enough so the object does not fall out but not so tight that it is deformed
• Never tighten the spindle using the barrel, only using the ratchet. This will reduce the chances of overtightening and zero errors

• The value measured from the micrometer is read where the thimble scale aligns with the main scale
• This should always be recorded to 2 decimal places (e.g. 1.40 mm not just 1.4 mm)

The micrometer reading is read when the thimble scale aligns with the main scale

#### Exam Tip

The most common mistake in exam answers when reading from a micrometer is not giving the reading to the correct number of significant figures! For a micrometer, this is always 3 significant figures. This is especially important for values such as '2.30 mm' where the 0 must be on the end to make it 3 sf instead of just 2 s.f (which would be 2.3 mm).

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