Measuring length, volume and time
International IGCSE Physics - separate from the Egyptian Baccalaureate / Thanaweya Amma syllabus. Physics begins with measurements. In this lesson, you will choose the right tool, read it carefully, and use a simple trick to measure things that are too small or quick to measure once.
Measure length from the scale, not the ruler’s edge
A length is the distance between two points. Use a ruler for short objects and a tape measure for longer distances. Put the zero mark (not automatically the physical end of the ruler) at one end of the object, then read the other end. Keep your eye directly above that mark.
Open the worked example
Suppose a pencil begins at 0.0 cm and ends at 12.4 cm. Its length is 12.4 − 0.0 = 12.4 cm. If it begins at 1.0 cm and ends at 13.4 cm, its length is still 13.4 − 1.0 = 12.4 cm.
Quick check: Why do we read with the eye directly above the scale mark?
Think, then reveal: Looking from the side changes the apparent position of the mark. This is parallax error.
Try the measurement ideas
Try the measuring-cylinder model
Move the liquid level. Practise looking at the bottom of the meniscus, with your eye level with that point.
The bottom of this model meniscus is at 40 cm³.
Practise water displacement
Adjust the two cylinder readings. Imagine the object is fully submerged with no air bubbles. Work out the rise in the water level.
Object volume = final reading − starting reading = 47 − 35 = 12 cm³
The object’s volume is the rise in the water reading, not the final reading by itself.
Explore why we time several swings
This model uses a pendulum period of 1.60 s and a reaction-time uncertainty of about 0.20 s. Change the number of swings timed.
Total time ≈ 1.60 s · reaction-time fraction ≈ 12.5%
More swings make the total time longer, so the same 0.20 s timing uncertainty is a smaller percentage. To get the period, divide the total time by 1.
Practise, then read the explanation
Choose an answer and submit it to see feedback. Or use “Study the answer” when you are reviewing.
Optional hint
Choose the instrument with a scale for liquid volume.
This lesson is an original explanation and practice set aligned to Cambridge IGCSE Physics 0625 objectives 1.1.1, 1.1.2 and 1.1.3. Use the supplied Volume A as the fuller reading; the page references above identify the matching section.