What are physical quantities in the context of Cambridge IGCSE Physics?

In Cambridge IGCSE Physics, physical quantities are properties of objects or phenomena that can be measured. They consist of a numerical magnitude and a unit. Examples include length, mass, time, and temperature. Understanding physical quantities is essential for studying topics like Motion, Forces, and Energy.

How do you differentiate between scalar and vector quantities in Physics?

Scalar quantities are physical quantities that have only magnitude, such as mass, temperature, and time. Vector quantities, on the other hand, have both magnitude and direction, such as velocity, force, and displacement. Recognizing the difference is crucial for solving problems related to Motion and Forces in the Cambridge IGCSE curriculum.

What are the standard units of measurement used in Cambridge IGCSE Physics?

The standard units of measurement in Cambridge IGCSE Physics are based on the International System of Units (SI). Key units include meters (m) for length, kilograms (kg) for mass, seconds (s) for time, and newtons (N) for force. Using these units ensures consistency and accuracy in scientific calculations.

Why is it important to understand measurement techniques in Physics?

Understanding measurement techniques is vital in Physics because accurate measurements are essential for conducting experiments and verifying theories. Techniques such as using a ruler for length, a stopwatch for time, and a balance for mass help ensure precision and reliability in scientific investigations, which is a key focus in the Cambridge IGCSE curriculum.

How do you convert units in Physics, and why is it necessary?

Unit conversion in Physics involves changing a measurement from one unit to another, such as from centimeters to meters. This is necessary to maintain consistency in calculations and to compare results accurately. Conversion factors, such as 1 meter = 100 centimeters, are used to perform these conversions, which is a fundamental skill in Cambridge IGCSE Physics.

Why is "Writing a numerical answer without the unit" a common mistake in Physical Quantities and Measurement Techniques?

Why it happens: Speed. How to avoid it: EVERY physics answer needs a unit. A bare number is automatically wrong. Source: 0625/42 — every series

Why is "Confusing $\text{m}$ (metres) with $\text{m}$ (milli prefix)" a common mistake in Physical Quantities and Measurement Techniques?

Why it happens: Same letter, different meaning depending on position. How to avoid it: Lower-case m before another unit = milli (10^-3). On its own = metres.

Why is "Adding vectors arithmetically (instead of with direction)" a common mistake in Physical Quantities and Measurement Techniques?

Why it happens: Treating them as scalars. How to avoid it: Vector sums need direction. Use a scale diagram or resolve into components.

Why is "Reporting more decimal places than the instrument allows" a common mistake in Physical Quantities and Measurement Techniques?

Why it happens: Calculator display has many digits. How to avoid it: Quote the answer to the same precision as the instrument's smallest division (e.g. 0.1\,cm for a typical ruler).

Motion, Forces and EnergyCambridge IGCSE Physics (0625)

Physical Quantities and Measurement Techniques

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Physical Quantities and Measurement Techniques — Cambridge IGCSE 0625 Physics Extended (2026)

SI units, prefixes, scalar vs vector, and how to measure length, volume, time and short intervals to the right precision. The toolkit underneath every physics calculation.

At a glance

SI base units: $\text{m}$ (length), $\text{kg}$ (mass), $\text{s}$ (time), $\text{A}$ (current), $\text{K}$ (temperature).
Derived units are combos: $\text{m/s}$ , $\text{N} = \text{kg}\,\text{m/s}^{2}$ , $\text{J} = \text{N m}$ .
Prefixes: $\text{n} = 10^{-9}, \mu = 10^{-6}, \text{m} = 10^{-3}, \text{k} = 10^{3}, \text{M} = 10^{6}, \text{G} = 10^{9}$ .
Scalar: magnitude only (mass, time, energy). Vector: magnitude AND direction (force, velocity, momentum).
Length: ruler ( $\text{mm}$ ), micrometer ( $0.01\,\text{mm}$ ), vernier ( $0.1\,\text{mm}$ ).
Time: average over many oscillations; reaction-time error matters.
Volume of a liquid: measuring cylinder, read at the bottom of the meniscus.
Volume of an irregular solid: displacement (water rises by the object's volume).

What you’ll learn

Mapped to the Cambridge IGCSE 0625 syllabus (2026-2028).

1.1 — Describe the use of rulers and measuring cylinders to find length and volume.
1.1 — Describe how to measure short intervals of time (e.g. period of a pendulum) by timing many oscillations.
1.2 — Distinguish between scalar and vector quantities and give examples.
1.2 — Add and subtract coplanar vectors using the parallelogram or tip-to-tail method.

SI units, prefixes and significant figures

Everything in physics measures back to a handful of base units. Prefixes scale them up or down by powers of 10.

SI base units to memorise.

Quantity	Symbol	SI unit
Length	$l$	metre, $\text{m}$
Mass	$m$	kilogram, $\text{kg}$
Time	$t$	second, $\text{s}$
Current	$I$	ampere, $\text{A}$
Temperature	$T$	kelvin, $\text{K}$

Prefixes.

$\text{n}$ (nano) $= 10^{-9}$
$\mu$ (micro) $= 10^{-6}$
$\text{m}$ (milli) $= 10^{-3}$
$\text{c}$ (centi) $= 10^{-2}$
$\text{k}$ (kilo) $= 10^{3}$
$\text{M}$ (mega) $= 10^{6}$
$\text{G}$ (giga) $= 10^{9}$

Worked. Convert $4.7\,\text{km}$ to metres, then to centimetres.

$4.7 \times 10^{3} = 4700\,\text{m}$ .
$4700 \times 100 = 470{,}000\,\text{cm}$ .

Significant figures. Cambridge Paper 4 expects answers to 3 s.f. unless told otherwise. Don't round inputs early.

Memorise the five SI base units.
Prefixes step in powers of $10$ .
Round to 3 s.f. unless asked otherwise.
Always include the unit on every numerical answer.

Scalars and vectors

Scalar = magnitude only. Vector = magnitude + direction. Add vectors tip-to-tail or by parallelogram.

Scalars have only a magnitude. Vectors have magnitude AND direction.

Scalar	Vector
Distance	Displacement
Speed	Velocity
Mass	Weight (force)
Energy	Force
Time	Acceleration
Temperature	Momentum

Adding vectors (parallelogram method). Draw both vectors from the same point, complete the parallelogram, draw the diagonal — that's the resultant.

Adding vectors (tip-to-tail). Place the tail of the second vector at the tip of the first; draw the resultant from the start of the first to the tip of the second.

Worked. A force of $3\,\text{N}$ east and a force of $4\,\text{N}$ north act on an object. Find the resultant.

Right-angled triangle: $R = \sqrt{3^{2} + 4^{2}} = 5\,\text{N}$ .
Direction: $\theta = \tan^{-1}(4/3) \approx 53.1\degree$ north of east.

At Extended level you also need: to find resultants when vectors are NOT perpendicular, by scale drawing or by splitting into components.

Scalar: magnitude only.
Vector: magnitude + direction.
Right-angled vectors: Pythagoras for magnitude.
Direction: $\tan^{-1}$ of opposite/adjacent.

Measuring length and time

Right tool for the right precision. Average many trials for time.

Length tools (in order of precision).

Metre ruler: precision $\pm 1\,\text{mm}$ .
Vernier callipers: precision $\pm 0.1\,\text{mm}$ (or 0.05).
Micrometer screw gauge: precision $\pm 0.01\,\text{mm}$ .

Use the most precise tool that fits the object's scale. Don't use a metre ruler for the diameter of a wire.

Avoid parallax error. Read the scale with your eye DIRECTLY in front of the mark — not at an angle.

Time intervals. A simple stopwatch has $\pm 0.1\,\text{s}$ resolution but reaction-time error is $\sim 0.2\text{-}0.3\,\text{s}$ . To find the period of a pendulum, time MANY oscillations and divide: $T = \dfrac{\text{total time}}{\text{number of oscillations}}.$

Worked. A pendulum completes 20 swings in $24.0\,\text{s}$ . Find the period.

$T = 24.0 / 20 = 1.20\,\text{s}$ .
Reaction error spread over 20 swings: $\pm 0.3 / 20 \approx \pm 0.015\,\text{s}$ — much better than timing one swing.

Match tool precision to object scale.
Avoid parallax — eye perpendicular to the scale.
Time many oscillations, divide by N.
Reaction-time error is reduced by averaging.

Measuring volume

Liquid: measuring cylinder. Irregular solid: water-displacement.

Liquid volume. Use a measuring cylinder. Read the level at the BOTTOM of the curved meniscus, eye level with the surface.

Regular solid volume. Use length measurements:

Cuboid: $V = lwh$ .
Cylinder: $V = \pi r^{2} h$ .
Sphere: $V = \dfrac{4}{3}\pi r^{3}$ .

Irregular solid volume. Water displacement:

Half-fill a measuring cylinder, record initial volume $V_{1}$ .
Lower the solid (sinker) gently into the water — make sure it's fully submerged.
Record new volume $V_{2}$ .
Volume of solid $= V_{2} - V_{1}$ .

Worked. Initial water level: $50\,\text{cm}^{3}$ . After dropping a stone in: $63\,\text{cm}^{3}$ .

Volume of stone: $63 - 50 = 13\,\text{cm}^{3}$ .

For a floating object: push it under with a needle / use a Eureka can with overflow spout.

Liquid: bottom of meniscus, eye level.
Regular solid: use the geometric formula.
Irregular solid: water displacement.
Floating object: hold under, or use Eureka can.

How it’s examined

Physical-quantities skills underpin every Paper 4 question — directly examined as 2-3 mark items (unit conversions, vector resolution, period of a pendulum) and indirectly in every calculation. Examiner reports flag missing units and unconverted prefixes as the top recurring losses.

Sources: Cambridge IGCSE Physics 0625 syllabus 2026-2028 (1.1-1.2); 0625/42 Oct/Nov 2024 — Q1 (vectors, units); 0625 Examiner Reports 2022-2024. Last reviewed 2026-05-06.

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Step-by-step worked examples — Physical Quantities and Measurement Techniques

Step-by-step solutions to past-paper-style questions on physical quantities and measurement techniques, written exactly the way a tutor would explain them at the board.

1Convert with SI prefixes
Core• units, prefix
Question
Convert $4.2 \,\text{km}$ into metres and $850 \,\text{mA}$ into amps.
Step-by-step solution
1. Step 1
  $1 \,\text{km} = 10^{3}\,\text{m}$ .
  $4.2 \,\text{km} = 4.2 \times 10^{3} = 4200\,\text{m}$
2. Step 2
  $1 \,\text{mA} = 10^{-3}\,\text{A}$ .
  $850 \,\text{mA} = 0.85\,\text{A}$
Answer
$4200\,\text{m}$ and $0.85\,\text{A}$
2Volume by water displacement
Core• Adapted from 0625/42 May/Jun 2024 Q1• volume
Question
A stone is lowered into a measuring cylinder. The water level rises from $40\,\text{cm}^{3}$ to $58\,\text{cm}^{3}$ . Find the volume of the stone.
Step-by-step solution
1. Step 1
  Volume = final − initial.
  $V = 58 - 40 = 18\,\text{cm}^{3}$
Answer
$18\,\text{cm}^{3}$
3Average time using multiple oscillations
Extended• time, pendulum
Question
A student times $20$ swings of a pendulum and gets $32.0\,\text{s}$ . Find the period $T$ .
Step-by-step solution
1. Step 1
  Divide total time by the number of swings.
  $T = \dfrac{32.0}{20} = 1.6\,\text{s}$
Answer
$T = 1.6\,\text{s}$
Examiner tip
Always time MULTIPLE oscillations and divide — reduces the impact of human reaction time.
4Identify scalar vs vector
Core• vector, scalar
Question
Classify each as vector or scalar: speed, velocity, distance, displacement, time, force.
Step-by-step solution
1. Step 1
  Vector = magnitude AND direction. Scalar = magnitude only.
Answer
Scalar: speed, distance, time. Vector: velocity, displacement, force.

Key Formulae — Physical Quantities and Measurement Techniques

The formulae you need to memorise for physical quantities and measurement techniques on the Cambridge IGCSE 0625 paper, with every variable defined in plain English and a note on when to use it.

Common SI prefixes
$\text{nano } 10^{-9},\ \mu\text{ } 10^{-6},\ \text{milli } 10^{-3},\ \text{kilo } 10^{3},\ \text{mega } 10^{6}$
When to use
Whenever converting between units that use prefixes.
Component form of a vector
$F_{x} = F\cos\theta,\ F_{y} = F\sin\theta$
$F$
magnitude of vector
$\theta$
angle from horizontal
When to use
Splitting a vector into perpendicular components.

Key Definitions and Keywords — Physical Quantities and Measurement Techniques

Definitions to memorise and the exact keywords mark schemes credit for physical quantities and measurement techniques answers — sharpened from recent examiner reports for the 2026 0625 sitting.

Physical quantity
Examiner keyword
A property that can be measured. Has a numerical value AND a unit.
Scalar
Examiner keyword
A quantity with magnitude only (no direction).
Vector
Examiner keyword
A quantity with both magnitude AND direction.
SI base units
Examiner keyword
Metre (m), kilogram (kg), second (s), ampere (A), kelvin (K), mole (mol). Other units derive from these.
Precision
How closely a set of measurements agree with one another (low spread). Different from accuracy.

Common Mistakes and Misconceptions — Physical Quantities and Measurement Techniques

The traps other students keep falling into on physical quantities and measurement techniques questions — taken from recent Cambridge IGCSE 0625 examiner reports and mark schemes — and how to avoid them.

✕Writing a numerical answer without the unit
0625/42 — every series
Why it happens
Speed.
How to avoid it
EVERY physics answer needs a unit. A bare number is automatically wrong.
✕Confusing $\text{m}$ (metres) with $\text{m}$ (milli prefix)
Why it happens
Same letter, different meaning depending on position.
How to avoid it
Lower-case m before another unit = milli ( $10^{-3}$ ). On its own = metres.
✕Adding vectors arithmetically (instead of with direction)
Why it happens
Treating them as scalars.
How to avoid it
Vector sums need direction. Use a scale diagram or resolve into components.
✕Reporting more decimal places than the instrument allows
Why it happens
Calculator display has many digits.
How to avoid it
Quote the answer to the same precision as the instrument's smallest division (e.g. $0.1\,\text{cm}$ for a typical ruler).

Practice questions

Exam-style questions with step-by-step worked solutions. Try one before checking the method.

Past paper style quiz

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Video lesson

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Physical Quantities and Measurement Techniques — frequently asked questions

The things students keep getting wrong in this sub-topic, answered.

Physical Quantities and Measurement Techniques

Short Study Notes in the form of Slides

Detailed Study Notes

What you’ll learn

How it’s examined

1Convert with SI prefixes

2Volume by water displacement

3Average time using multiple oscillations

4Identify scalar vs vector

Common SI prefixes

Component form of a vector

Physical quantity

Scalar

Vector

SI base units

Precision

✕Writing a numerical answer without the unit

✕Confusing m\text{m}m (metres) with m\text{m}m (milli prefix)

✕Adding vectors arithmetically (instead of with direction)

✕Reporting more decimal places than the instrument allows

Practice questions

Past paper style quiz

Assess your understanding

Video lesson

Physical Quantities and Measurement Techniques — frequently asked questions

✕Confusing $\text{m}$ (metres) with $\text{m}$ (milli prefix)