🌈 Screw Gauge Mind Map | Class 9 Physics Made Easy

Rainbow Mind Map: Screw Gauge

1. Definition

A screw gauge is a device used to measure very small lengths or thicknesses (up to 0.01 mm or 0.001 cm) with high accuracy.

2. Main Parts

• U-shaped Frame
• Thimble
• Sleeve (Main Scale)
• Ratchet

3. Pitch of the Screw

• Distance moved by the spindle in one complete rotation
• Pitch = Distance moved / Number of rotations

4. Least Count

• Smallest value the instrument can measure
• Least Count = Pitch / Number of divisions on circular scale
• Usually 0.01 mm or 0.001 cm

5. Uses

• Measuring thickness of a wire
• Measuring diameter of small spherical objects
• Measuring thickness of thin sheets

6. Zero Error

• If zero of circular scale doesn’t coincide with baseline on main scale
• Types: Positive, Negative, or Zero
• Must be corrected in final reading

7. Formula for Total Reading

• Total = Main Scale Reading (MSR) + (Circular Scale Reading × Least Count)
• Final Measurement = Total Reading ± Zero Error

Your Turn!
Can you calculate the diameter of a wire if the main scale reads 2.5 mm, circular scale reads 35, and least count is 0.01 mm?

Comment your answer below and see who gets it right first!