Q1
Parallax error occurs due to:
Aincorrect eye position while reading a scale
Busing a broken ruler
Cmeasuring a curved object
Dusing a metric scale
CBSEClass 6 (CBSE)ScienceCh 5 · Topic 2
Measuring Length Correctly
Learning the correct technique to measure length using a scale.
Core concept
To avoid parallax error, always look straight down at the measurement mark, with your eye level directly above the scale — not from an angle. When measuring curved or irregular objects, a flexible measuring tape works better than a rigid ruler, since it can bend along the curve. For very small measurements, more precise instruments like a vernier caliper are used instead of an ordinary ruler, as they can measure to a fraction of a millimetre.
Exam highlight
Key diagram
- Show correct vs incorrect eye position while reading a ruler, illustrating parallax error.
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Quick notes
• Align the ruler's zero mark exactly with the starting point of the object.
• Parallax error occurs when the eye is not directly above the scale reading.
• Flexible measuring tapes are better for curved or irregular objects.
• Vernier calipers are used for very precise, small measurements.