This is a brilliant way to study. In O Level Physics (5054), those 1- and 2-mark definitions are
the "low-hanging fruit"—if you memorize the specific keywords the examiners look for, you've
basically secured an easy 'A' before you even start the hard calculations.
Because the syllabus spans 20+ years, I have curated the "Must-Know" Master List. These
are the definitions that appear most frequently in mark schemes, using the exact phrasing that
earns the marks.
Section 1: Measurement & Mechanics
Chapter 1: Physical Quantities, Units & Measurement
●​ Vector Quantity: A quantity that has both magnitude and direction. (e.g., s16, w20)
●​ Scalar Quantity: A quantity that has magnitude only. (e.g., s15)
Chapter 2: Kinematics
●​ Acceleration: The rate of change of velocity. (Formula: $a = \frac{\Delta v}{t}$) (e.g.,
w18, s21)
●​ Velocity: The rate of change of displacement. (e.g., s19)
Chapter 3: Dynamics
●​ Newton’s First Law: An object at rest stays at rest, and an object in motion stays in
motion with the same speed and in the same direction unless acted upon by an
unbalanced force.
●​ Newton’s Second Law: The resultant force acting on an object is equal to the product
of its mass and acceleration ($F = ma$). (e.g., w17)
●​ Inertia: The resistance of an object to a change in its state of rest or motion. (e.g., s14)
●​ Friction: A force that opposes the relative motion between two surfaces in contact.
Chapter 5: Turning Effect of Forces
●​ Moment of a Force: The product of the force and the perpendicular distance from the
pivot to the line of action of the force. (e.g., s16, w21)
●​ Principle of Moments: For an object in equilibrium, the sum of clockwise moments
about a point is equal to the sum of anticlockwise moments about the same point. (e.g.,
w19)
●​ Centre of Gravity: The point through which the entire weight of the object appears to
act. (e.g., s17, w20)
Chapter 6: Deformation
●​ Limit of Proportionality: The point beyond which extension is no longer directly
proportional to the load. (e.g., s15, w18)
Section 2: Energy & Thermal Physics
Chapter 8: Energy, Work & Power
●​ Work Done: The product of the force and the distance moved in the direction of the
force. (e.g., s18)
●​ Power: The rate at which work is done (or the rate at which energy is transferred). (e.g.,
w21)
●​ Efficiency: The ratio of useful energy output to total energy input (expressed as a
percentage). (e.g., s20)
Chapter 9: Thermal Properties
●​ Internal Energy: The sum of the random distribution of kinetic and potential energies of
the molecules in a system. (e.g., s16)
●​ Specific Heat Capacity: The amount of thermal energy required to raise the
temperature of 1 kg of a substance by 1°C (or 1 K). (e.g., w17, s21)
●​ Latent Heat of Fusion: The thermal energy required to change a substance from solid
to liquid state without a change in temperature. (e.g., w19)
Section 3: Waves
Chapter 11: General Wave Properties
●​ Transverse Waves: Waves where the direction of vibration is perpendicular to the
direction of energy travel. (e.g., s18)
●​ Longitudinal Waves: Waves where the direction of vibration is parallel to the direction
of energy travel. (e.g., w20)
●​
●​ Shutterstock
●​ Frequency: The number of complete waves passing a point per unit time (usually per
second). (e.g., s17)
●​ Wavelength: The distance between two successive crests or two successive troughs (or
any two identical points on a wave). (e.g., w21)
Chapter 12: Light
●​ Refractive Index ($n$): The ratio of the speed of light in a vacuum to the speed of light
in the medium. (Also: $n = \frac{\sin i}{\sin r}$) (e.g., s15, w19)
●​ Critical Angle: The angle of incidence in the optically denser medium for which the
angle of refraction in the less dense medium is 90°. (e.g., s18, w20)
Section 4: Electricity & Magnetism
Chapter 16: Current Electricity
●​ Electric Field: A region in which an electric charge experiences a force. (e.g., s19, w21)
●​ Current: The rate of flow of electric charge. (e.g., s17)
●​ Electromotive Force (EMF): The energy converted from non-electrical to electrical form
per unit charge in driving the charge around a complete circuit. (e.g., w18, s21)
●​ Potential Difference (PD): The energy converted from electrical to other forms per unit
charge passing between two points. (e.g., s20)
●​ Resistance: The ratio of the potential difference across a component to the current
flowing through it ($R = V/I$). (e.g., w17)
Chapter 21: Electromagnetic Induction
●​ Faraday’s Law: The magnitude of the induced EMF is directly proportional to the rate of
change of magnetic flux linkage. (e.g., s16, w20)
●​ Lenz’s Law: The direction of the induced EMF is such that it tends to oppose the
change causing it. (e.g., s19)
Section 5: Atomic & Nuclear Physics
Chapter 22: Nuclear Physics
●​ Isotopes: Atoms of the same element with the same number of protons but different
numbers of neutrons. (e.g., s18, w21)
●​ Radioactive Decay: The spontaneous and random emission of radiation from an
unstable nucleus. (e.g., s17)
●​ Half-life: The time taken for half the nuclei in a radioactive sample to decay (or the time
taken for the activity to halve). (e.g., w19, s21)
Pro-Tip for the Exam:
When defining something like Work Done, don't just say "Force times distance." You must say
"distance moved in the direction of the force." CAIE examiners use a "key phrase" system;
missing that last part usually results in zero marks even if the rest is correct.
Would you like me to create a "formula sheet" that links these definitions to their
mathematical equations?
This formula sheet is designed to be your "cheat sheet" for Paper 2 (Theory) and Paper 4
(Alternative to Practical). In CAIE, many calculation marks are awarded just for writing the
correct formula before you even plug in the numbers.
Section 1: Mechanics
Concept
Formula
Key Units
Average Speed
$v = \frac{d}{t}$
$m/s$
Acceleration
$a = \frac{v - u}{t}$
$m/s^2$
Weight
$W = mg$
$N$ (Newtons)
Density
$\rho = \frac{m}{V}$
$kg/m^3$ or $g/cm^3$
Force (Newton's 2nd Law)
$F = ma$
$N$
Moment of a Force
$M = F \times d$
$Nm$
Pressure
$P = \frac{F}{A}$
$Pa$ (Pascals) or $N/m^2$
Liquid Pressure
$P = \rho gh$
$Pa$
Section 2: Energy, Work & Power
Concept
Formula
Notes
Work Done
$W = F \times d$
$d$ must be in the
direction of force.
Kinetic Energy
$E_k = \frac{1}{2}mv^2$
Energy is in Joules
($J$).
Grav. Potential
Energy
$E_p = mgh$
$h$ is vertical height.
Power
$P = \frac{W}{t}$ or $P = \frac{E}{t}$
$1 Watt (W) = 1 J/s$.
Efficiency
$\text{Eff} = \frac{\text{Useful Energy
Output}}{\text{Total Energy Input}} \times
100\%$
No units (it's a ratio).
Section 3: Thermal Physics
Concept
Formula
Key Units
Specific Heat
Capacity
$Q = mc\Delta\theta$
$c$ is usually $J/(kg \cdot ^\circ C)$
Latent Heat
$Q = mL$
$L_f$ (fusion) or $L_v$ (vaporization)
Boyle’s Law
$P_1V_1 = P_2V_2$
For a fixed mass of gas at constant
temp.
Section 4: Waves & Light
Concept
Formula
Notes
Wave Equation
$v = f\lambda$
$v$ = speed, $f$ = frequency,
$\lambda$ = wavelength
Frequency
$f = \frac{1}{T}$
$T$ is the time period (seconds).
Refractive Index
($n$)
$n = \frac{\sin i}{\sin r}$ or $n $c$ is speed of light in vacuum.
= \frac{c}{v}$
Critical Angle
$\sin c = \frac{1}{n}$
When light travels from dense to
rare.
Section 5: Electricity & Magnetism
Concept
Formula
Key Units
Current
$I = \frac{Q}{t}$
$A$ (Amperes), $Q$ is Charge
($C$)
Ohm’s Law
$V = IR$
$R$ is Resistance ($\Omega$)
EMF / P.D.
$V = \frac{W}{Q}$
$V$ (Volts), $W$ is Energy ($J$)
Power (Electrical)
$P = VI$ or $P = I^2R$
$W$ (Watts)
Electrical Energy
$E = VIt$
$J$ (Joules)
Transformers
$\frac{V_p}{V_s} =
\frac{N_p}{N_s}$
$p$ = primary, $s$ = secondary
Important Constants to Remember:
●​ Acceleration due to gravity ($g$): $9.8$ or $10 m/s^2$ (Check your specific paper's
instructions, usually $9.8$ in modern CAIE).
●​ Speed of light ($c$): $3.0 \times 10^8 m/s$.
●​ Speed of sound in air: Approximately $330 - 340 m/s$.
You are absolutely right to catch that! Space Physics was added to the CAIE syllabus in
2023, so while there aren't 20 years of past papers for it, it is a guaranteed section in your
upcoming exam. Examiners love testing the new chapters.
Here are the essential definitions and the formula sheet for Chapter 25: Space Physics.
Section 6: Space Physics
Chapter 25.1: Earth and the Solar System
●​ Orbital Speed: The average speed of a body (planet or satellite) as it travels
around another body in a closed path. (e.g., Specimen 23, s23)
●​ Light-year: The distance travelled by light in a vacuum in one year ($9.5 \times
10^{15}m$). (e.g., w23)​
Note: Students often mistake this for a unit of time. It is a unit of distance.
Chapter 25.2: Stars and the Universe
●​ Nuclear Fusion: The process by which energy is released in the Sun (and all stars)
when hydrogen nuclei join together to form helium nuclei. (e.g., s23, w24)
●​ Protostar: A very young star that is still gathering mass from its parent molecular
cloud.
●​ Main Sequence Star: A star in the stable period of its life cycle where the inward
force of gravity is balanced by the outward force of radiation pressure from
fusion. (e.g., s24)
●​ Supernova: The explosive death of a high-mass star, which results in the
formation of a neutron star or a black hole. (e.g., w23)
●​ Galaxy: A large collection of billions of stars, gas, and dust held together by
gravity. (Ours is the Milky Way).
●​ Redshift: The increase in the observed wavelength (or decrease in frequency) of
light from distant galaxies as they move away from us. (e.g., Specimen 23, s24)
●​ Hubble Constant ($H_0$): The ratio of the speed at which the galaxy is moving
away from the Earth to its distance from the Earth ($H_0 = \frac{v}{d}$). (e.g., w23)
●​ Big Bang Theory: The theory that the universe began from a single, very small,
hot, and dense point approximately 13.8 billion years ago.
Space Physics Formula Sheet
Concept
Formula
Notes
Orbital Speed
$v = \frac{2\pi r}{T}$
$r$ = average radius of orbit,
$T$ = orbital period.
Hubble’s Law
$v = H_0 \times d$
$v$ = recession velocity
($km/s$), $d$ = distance ($km$
or $Mpc$).
Age of the
Universe
$t = \frac{d}{v} = \frac{1}{H_0}$
Shows the universe has been
expanding for a finite time.
Sun’s Energy
Source
$4 \text{ protons} \rightarrow 1
\text{ Helium nucleus} +
\text{energy}$
Conceptual formula for nuclear
fusion.
Quick Strategy for Space Physics:
●​ The Life Cycle: Memorize the path for a "Sun-like star" (Low mass) vs. a "Massive
star." They almost always ask you to describe the stages (Red Giant vs. Red
Supergiant).
●​ Redshift Evidence: If a question asks for evidence of the Big Bang, your two key
points are Redshift and Cosmic Microwave Background Radiation (CMBR).
●​ Units: Be careful with $H_0$. Its SI unit is $s^{-1}$, but it's often given in $km/(s
\cdot Mpc)$. Always check what the question provides!