IGCSE Physics: Physical Quantities and Measurement Practice Questions
Every physical quantity has a magnitude and a unit. Scalar quantities have magnitude only, while vector quantities have both magnitude and direction, which is why forces and velocities must be added taking direction into account.
Sub-topic 1.1 of Cambridge IGCSE Physics 0625 supplies techniques used in every practical question on Papers 5 and 6. The recurring theme is reducing the effect of measurement uncertainty by measuring many items or many repeats. The questions below train that idea and the scalar and vector distinction.
What you need to know for Physical Quantities and Measurement Techniques
- Measuring small lengthsMeasure a large number of identical items together and divide. Measuring 100 sheets of paper and dividing by 100 gives a far more reliable thickness than measuring one sheet.
- Measuring short time intervalsTime many oscillations and divide by the number. Timing 20 swings of a pendulum and dividing by 20 reduces the effect of reaction time on each measurement.
- Zero errorA systematic error where an instrument does not read zero when it should. Check the reading before use and subtract it from every measurement.
- VolumeA regular solid: multiply the dimensions. An irregular solid: use displacement in a measuring cylinder or a displacement can. A liquid: read from a measuring cylinder at eye level from the bottom of the meniscus.
- Scalar quantitiesDistance, speed, mass, time, energy and temperature. They have magnitude only.
- Vector quantitiesDisplacement, velocity, acceleration, force, weight and momentum. They have magnitude and direction, and can be added by scale drawing or by calculation when perpendicular.
IGCSE Physics Physical Quantities and Measurement Techniques questions and answers
4 exam-style questions written to the 0625 syllabus. Try each one on paper first, then open the worked answer to check your method against the marks.
A student wants to find the thickness of one sheet of paper using a ruler that measures to the nearest millimetre. Describe how she should do it and explain why this method is better than measuring one sheet.
Show the worked answer
- Stack a known large number of identical sheets, for example 100, and press them together so there are no air gaps.
- Measure the total thickness of the stack with the ruler.
- Divide the total thickness by the number of sheets to find the thickness of one sheet.
- One sheet is far thinner than the smallest division on the ruler, so measuring it directly gives an uncertainty as large as the measurement itself. Measuring 100 sheets gives a reading of a few millimetres, and dividing by 100 also divides the uncertainty by 100, so the result is much more reliable.
A student measures the period of a pendulum. Explain why she times 20 complete oscillations rather than one, and describe one other way she could improve the reliability of her result.
Show the worked answer
- Human reaction time introduces an error of roughly 0.2 seconds each time the stopwatch is started or stopped.
- One oscillation may take under a second, so that error would be a large proportion of the reading.
- Timing 20 oscillations gives a much longer total time, and dividing by 20 also divides the reaction time error by 20, so the period is much more reliable.
- She could also repeat the whole measurement several times and calculate a mean, and use a fiducial marker at the centre of the swing to judge the start and end points consistently.
Explain the difference between a scalar and a vector quantity, and classify speed, velocity, mass and weight as one or the other.
Show the worked answer
- A scalar quantity has magnitude only. Stating the number and the unit describes it completely.
- A vector quantity has both magnitude and direction, so the direction must be stated for the description to be complete.
- Speed is a scalar because it tells you how fast without saying which way. Mass is a scalar because it has no direction.
- Velocity is a vector because it is speed in a stated direction. Weight is a vector because it is a force, and it always acts downwards towards the centre of the Earth.
Two forces act on an object at a point. A force of 3.0 N acts due east and a force of 4.0 N acts due north. Calculate the magnitude of the resultant force.
Show the worked answer
- The two forces are perpendicular, so they can be combined using Pythagoras' theorem rather than a scale drawing.
- Resultant squared = 3.0 squared + 4.0 squared = 9.0 + 16.0 = 25.0.
- Resultant = square root of 25.0 = 5.0 N.
- The direction is north east of due east, at an angle whose tangent is 4.0 divided by 3.0, which is 53 degrees north of east.
Common mistakes in this topic
- Adding vectors arithmetically when they act in different directions.
- Forgetting to check for zero error before taking readings.
- Reading a measuring cylinder from the top of the meniscus, or not at eye level.
- Timing a single oscillation rather than many.
- Quoting a measurement without a unit.
Exam tips
- For any small quantity, measure many and divide. State that this reduces the percentage uncertainty.
- Always name the instrument as well as the method. Metre rule, measuring cylinder, stopwatch, displacement can.
- Learn the scalar and vector lists as two columns. It is worth an easy mark.
- For perpendicular vectors use Pythagoras. For any other angle use a scale drawing with a stated scale.
- Give answers to the same number of significant figures as the data provided, usually two or three.
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Physical Quantities and Measurement Techniques FAQs
What is the difference between a scalar and a vector?
A scalar quantity has magnitude only, such as mass, speed, time and energy. A vector quantity has both magnitude and direction, such as force, weight, velocity, acceleration and momentum. Vectors must be combined taking direction into account rather than simply added.
Why time 20 oscillations instead of one?
Human reaction time adds an error of roughly 0.2 seconds each time the stopwatch is used, which would be a large proportion of a single short measurement. Timing 20 oscillations gives a much longer total, and dividing by 20 divides that error by 20 as well, so the calculated period is far more reliable.
How do I measure the volume of an irregular solid?
Part fill a measuring cylinder with water and record the volume. Lower the solid in fully and record the new volume. The difference is the volume of the solid. Alternatively use a displacement can and collect the overflow in a measuring cylinder.
How do I find the resultant of two perpendicular forces?
Use Pythagoras' theorem: square each force, add them, and take the square root. For the direction, use the inverse tangent of one force divided by the other. For forces that are not perpendicular, draw a scale diagram and measure the resultant.
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Written to the published Cambridge IGCSE Physics (0625) syllabus. Check your school entry code and syllabus year, because Core and Extended candidates are assessed on different content. Last reviewed 2026-08-12.