Measurement of Length and Motion Part 1: MCQs (Q1–Q25)
Part 1 — Questions 1–25 (Units of length, standard units, measuring instruments)
1. The SI unit of length is
A. Gram
B. Second
C. Metre (m) ← Correct answer: C
D. Litre
Explanations:
A) Incorrect — gram is unit of mass.
B) Incorrect — second is unit of time.
C) Correct — the metre is the SI base unit for length.
D) Incorrect — litre is for volume.
2. Which one is the smallest among these units of length?
A. Kilometre
B. Metre
C. Centimetre
D. Millimetre (mm) ← Correct answer: D
Explanations:
A) Incorrect — 1 km = 1,000 m (largest).
B) Incorrect — metre larger than cm and mm.
C) Incorrect — 1 cm = 10 mm.
D) Correct — millimetre is smallest (1 m = 1000 mm).
3. Which instrument is best to measure the length of a classroom blackboard?
A. Vernier caliper
B. Micrometer screw gauge
C. Measuring tape (or metre scale) ← Correct answer: C
D. A thermometer
Explanations:
A/B) Incorrect — these are for small, precise measurements.
C) Correct — measuring tape/metre scale suitable for long objects.
D) Incorrect — thermometer measures temperature.
4. A metre scale shows divisions up to centimetres and millimetres. How many millimetres are there in 1 cm?
A. 100 mm
B. 10 mm ← Correct answer: B
C. 1 mm
D. 0.1 mm
Explanations:
A) Incorrect — 100 mm = 10 cm.
B) Correct — 1 cm = 10 mm.
C) Incorrect — 1 mm is the smallest unit here.
D) Incorrect — 0.1 mm is tenth of mm.
5. Which device gives the most precise measurement for the diameter of a thin wire?
A. Ruler
B. Measuring tape
C. Micrometer screw gauge ← Correct answer: C
D. Stop watch
Explanations:
A/B) Not precise for very small diameters.
C) Correct — micrometer measures small thicknesses to 0.01 mm accuracy.
D) Incorrect — stopwatch measures time.
6. A vernier caliper is used to measure
A. Volume of liquids only
B. External and internal diameters and depths (lengths) ← Correct answer: B
C. Temperature only
D. Mass only
Explanations:
A/C/D) Incorrect.
B) Correct — vernier caliper measures external/internal dimensions and depth with precision.
7. Which reading instrument is used to measure small lengths like wire diameter to a high precision (usually 0.01 mm)?
A. Ruler
B. Micrometer screw gauge ← Correct answer: B
C. Tape measure
D. Balance
Explanations:
A/C) Less precise.
B) Correct — micrometer provides high precision for small lengths.
D) Incorrect — balance measures mass.
8. A student measures a pencil length as 12.3 cm using a ruler. The .3 in 12.3 represents
A. 3 metres
B. 3 millimetres ← Correct answer: B
C. 30 centimetres
D. 0.3 metre
Explanations:
A) Incorrect.
B) Correct — 12.3 cm = 12 cm + 0.3 cm = 12 cm + 3 mm.
C/D) Incorrect scale conversions.
9. Which statement is TRUE about estimation before measuring?
A. Estimation wastes time always
B. Estimation gives a rough idea and helps choose correct measuring range/instrument ← Correct answer: B
C. Estimation replaces the need for measurement
D. Estimation always gives exact value
Explanations:
A/C/D) Incorrect.
B) Correct — estimation helps plan measurement and detect large errors.
10. Which instrument would you use to measure the length of a biological specimen under microscope?
A. Measuring tape
B. Vernier caliper or an ocular/micrometer scale (microscope scale) ← Correct answer: B
C. Stopwatch
D. Thermometer
Explanations:
A) Too coarse.
B) Correct — microscope-based scales or vernier suitable for small specimens.
C/D) Not length instruments.
11. Which is NOT a standard unit of length?
A. Metre
B. Kilometre
C. Foot (in SI context) ← Correct answer: C
D. Centimetre
Explanations:
A/B/D) SI units or derived metric units (km is 1000 m).
C) Correct — foot is not an SI unit (it is imperial).
12. A student finds length of a book as 24.0 cm and another finds 24.00 cm using vernier. The difference is mainly due to
A. Different units used
B. Different precision (instrument accuracy) ← Correct answer: B
C. One student lied
D. None of the above
Explanations:
A) Units same (cm).
B) Correct — more decimal places indicate higher precision from vernier.
C/D) Incorrect.
13. When using a metre scale, parallax error occurs because of
A. Incorrect units on scale
B. Observer’s eye not positioned perpendicular to the scale reading ← Correct answer: B
C. Scale not long enough only
D. Scale melting
Explanations:
A/C/D) Incorrect.
B) Correct — parallax occurs when viewing angle misreads the mark.
14. Which is the best method to reduce parallax error when reading a scale?
A. Read from any angle
B. Keep eye level directly above the scale mark ← Correct answer: B
C. Close one eye and look at far away object
D. Read value upside down
Explanations:
A/C/D) Incorrect.
B) Correct — eye directly perpendicular to scale removes parallax.
15. The length of a pen measured with a metre scale is 14.8 cm. What is the length in millimetres?
A. 1480 mm
B. 148 mm ← Correct answer: B
C. 1.48 mm
D. 14.8 mm
Explanations:
A) 1480 mm = 148 cm (wrong).
B) Correct — 14.8 cm × 10 = 148 mm.
C/D) Incorrect unit conversions.
16. Which device is best to measure the internal diameter of a pipe?
A. Ruler placed outside pipe
B. Vernier caliper (internal jaws) ← Correct answer: B
C. Stopwatch
D. Magnet
Explanations:
A) Not accurate for internal dimension.
B) Correct — calipers have internal jaws for such measurement.
C/D) Irrelevant.
17. What is the least count of a standard metre (plastic) scale that has smallest division 1 mm?
A. 1 metre
B. 1 millimetre (0.1 cm) ← Correct answer: B
C. 0.01 mm
D. 10 cm
Explanations:
A/C/D) Incorrect.
B) Correct — least count equals smallest marked division = 1 mm.
18. To measure the length of a curved object like a piece of rope, you should use
A. Vernier caliper only
B. Micrometer screw gauge only
C. Measuring tape (flexible tape) ← Correct answer: C
D. Thermometer
Explanations:
A/B) Not suitable for flexible curves.
C) Correct — flexible tape follows curve for accurate length.
D) Irrelevant.
19. Which among the following is NOT measured in metres?
A. Height of a tree
B. Distance between two cities
C. Mass of a stone ← Correct answer: C
D. Length of classroom
Explanations:
A/B/D) Length/distance measured in metres (or km).
C) Correct — mass measured in kilograms/grams, not metres.
20. Which property of instrument defines how small a change it can detect?
A. Colour
B. Least count (precision) ← Correct answer: B
C. Weight only
D. Length only
Explanations:
A/C/D) Irrelevant.
B) Correct — least count indicates smallest measurable increment (precision).
21. 0.005 m equals how many millimetres?
A. 0.5 mm
B. 5 mm ← Correct answer: B
C. 50 mm
D. 500 mm
Explanations:
A) Incorrect conversion.
B) Correct — 0.005 m = 5 mm (since 1 m = 1000 mm).
C/D) Incorrect.
22. The purpose of calibrating a measuring instrument is to
A. Make it colourful
B. Ensure correct and accurate readings against a standard ← Correct answer: B
C. Change its unit system randomly
D. Break it purposely
Explanations:
A/C/D) Incorrect.
B) Correct — calibration aligns instrument with known standard.
23. While using a vernier caliper, the zero error is checked to ensure
A. The instrument is clean only
B. The zero on main scale and zero on vernier coincide when jaws fully closed ← Correct answer: B
C. The instrument is heavy
D. The instrument is magnetic
Explanations:
A/C/D) Not core reason.
B) Correct — zero error affects accuracy and must be accounted.
24. Which of the following is true for micrometer screw gauge?
A. It measures very long distances
B. It measures small lengths with high precision using screw mechanism ← Correct answer: B
C. It measures time intervals
D. It is same as a ruler
Explanations:
A/C/D) Incorrect.
B) Correct — micrometer gives fine measurements using screw pitch.
25. A student measures length repeatedly with different instruments and gets slightly different values. The best scientific response is to
A. Ignore differences and pick favourite value
B. Record all readings, calculate average and note instrument precision ← Correct answer: B
C. Burn the instruments
D. Say measurement is impossible
Explanations:
A/C/D) Not scientific.
B) Correct — averaging and noting precision improves reliability and documents uncertainty.