1. Unit 1: Measurements
Measurement of Length

2. What are we learning today?
Instruments used to measure length
Accuracy / Precision
Errors
Vernier calipers
Micrometer Screw Gauge

3. Instruments to measure length
Measuring tape is used to measure the distance a ball thrown.
Metre rule is used to measure the length and breadth of a table.
Vernier calipers is used to measure the diameter of a coin/rod.
Micrometer screw gauge is used to measure the thickness of papers.

4. Accuracy / Precision
Precision / Accuracy of an instrument is the smallest unit it can accurately measure.

5. Instruments used to measure length
Accuracy / Precision
Instruments used to measure length
Precision / Accuracy
Measuring tape
0.1 cm
Metre rule
Vernier calipers
0.01 cm
Micrometer screw guage
0.001 cm / 0.01 mm

6. Errors
Parallax Error
Human
Zero Error
Instrument

7. Errors To avoid parallax error:
The eye must be positioned vertically above the mark on the scale.
Several readings and the average must be taken.

8. Vernier Calipers
Vernier calipers consist of a main scale and a sliding vernier scale.

9. Vernier Calipers
Vernier calipers are used to measure the internal diameters, external diameters and depth of an object.

10. Vernier Calipers The procedure of reading a vernier calipers:
Read the main scale opposite the zero mark of the vernier scale. This will give value up to one decimal place.
Look out for the vernier mark that coincides with the marking on the main scale. This will give the value for the second decimal place.

11. Reading The Vernier Calipers
MAIN SCALE
VERNIER SCALE 2 3 1
Step 1
Step 2

12. Reading The Vernier Calipers
Step 1
Step 2
Step 1: Reading = 0.1_ cm
Step 2: Reading = 0.15 cm

13. Reading The Vernier Calipers
Step 1
Step 2
Step 1: Reading = 4.1_ cm
Step 2: Reading = 4.17 cm

14. Reading The Vernier Calipers
Step 1
Step 2
Step 1: Reading = 2.5_ cm
Step 2: Reading = 2.55 cm

15. Reading The Vernier Calipers
Step 1
Step 2
Step 1: Reading = 0.8_ cm
Step 2: Reading = 0.84 cm

16. Micrometer Screw Gauge
Micrometer screw gauge is used to measure anything less than 1 cm and is too small for the vernier calipers to measure.

17. Micrometer Screw Gauge
The procedure of reading a micrometer screw gauge:
Read the main scale at the edge of the thimble. This will give value up to one decimal place in millimetres.
The thimble scale has 50 divisions, each of which is 0.01 mm. Look out for the thimble mark that coincides with the datum line. This will give the value for the second decimal place in millimetres.

18. Reading The Micrometer Screw Gauge
Step 1: Reading
= 0.2__ cm
Step 2: Reading
= cm
Step 1
Step 2

19. Reading The Micrometer Screw Gauge
Step 1: Reading
= 0.35_ cm
Step 2: Reading
= cm
Step 2
Step 1

20. Reading The Micrometer Screw Gauge
Step 1: Reading
= 0.1__ cm
Step 2: Reading
= cm
Step 1
Step 2

21. Reading The Micrometer Screw Gauge
Step 1: Reading
= 0.15_ cm
Step 2: Reading
= cm
Step 1
Step 2

22. Pop Quiz #1
A piece of paper is m long, 35.2 mm wide and 1.5 mm thick. What is the appropriate instrument for measuring (a) the length, (b) width and (c) thickness?
Which instrument can be used to measure the internal diameter of a measuring cylinder?