Physics is one of the most rewarding — and most demanding — subjects in the Singapore O-Level curriculum. Whether you are tackling Pure Physics (6091) or Combined Science, success hinges on one thing: building a clear, connected understanding of every topic before exam day arrives. That is exactly what this set of O-Level Physics notes is designed to help you do.

This guide covers all the major topic areas in syllabus order — from Measurement right through to Radioactivity — giving you the essential definitions, key concepts and core formulas you need for each chapter. Rather than a passive list of facts, these notes are structured to help you see how ideas connect across topics, which is the approach that consistently separates A1 students from the rest. Bookmark this page, work through it alongside your school notes, and use it as a quick-reference companion during revision.

Why Organised Physics Notes Make a Difference

Many students underestimate the role that well-structured notes play in exam performance. When you organise your revision material by topic, you can identify weak areas quickly, review definitions in the exact phrasing examiners expect, and apply formulas accurately under timed conditions. Physics topics are deeply interconnected — a shaky foundation in Kinematics will affect your ability to handle Dynamics questions, just as gaps in basic circuit theory will slow you down across the entire Electricity and Magnetism section. Building clear, topic-by-topic notes from Secondary 3 gives you a cumulative advantage that compounds right up to the O-Level papers.

The syllabus is organised into six broad sections: Measurement, Newtonian Mechanics, Thermal Physics, Waves, Electricity and Magnetism, and Radioactivity. The notes below follow this order, so you can work through them in sequence or jump directly to a topic you are revising. If you are looking for more structured support alongside your own revision, the secondary tuition programme at EduFirst provides personalised guidance through every topic with class sizes of just 4 to 8 students.

Topic 1: Measurement

Measurement is the foundation of all Physics. Before any calculation can be made, you need to be confident working with SI units, understanding prefixes and reading measuring instruments accurately. Errors here carry through to every other topic, so it is worth getting this foundation absolutely solid early in Secondary 3.

Key Concepts and Definitions

• SI Base Units: The standard units used in Physics — kilogram (kg) for mass, metre (m) for length, second (s) for time, ampere (A) for current, kelvin (K) for temperature.
• Scalar quantity: A quantity that has magnitude only (e.g. mass, distance, speed, time).
• Vector quantity: A quantity that has both magnitude and direction (e.g. displacement, velocity, acceleration, force).
• Precision: Determined by the smallest division of the measuring instrument being used.
• Common prefixes: nano (n) = 10⁻⁹, micro (μ) = 10⁻⁶, milli (m) = 10⁻³, centi (c) = 10⁻², kilo (k) = 10³, mega (M) = 10⁶.

Measuring instruments tested in O-Level Physics include the ruler (1 mm precision), vernier calliper (0.1 mm precision), and micrometer screw gauge (0.01 mm precision). Always state the instrument and its precision when asked about experimental method in Paper 2 or Paper 3 practical questions.

Topic 2: Kinematics

Kinematics deals with the description of motion — how objects move — without considering the forces that cause that motion. It is one of the most heavily tested areas in O-Level Physics and forms the launchpad for Dynamics, so mastering it early pays dividends throughout your revision.

Key Definitions

• Distance: The total path length travelled (scalar).
• Displacement: The straight-line distance from start to finish in a specified direction (vector).
• Speed: The rate of change of distance with time (scalar).
• Velocity: The rate of change of displacement with time (vector).
• Acceleration: The rate of change of velocity with time (vector).

Core Formulas

• Average speed = Total distance ÷ Total time
• Acceleration: a = (v − u) ÷ t
• For uniform acceleration (equations of motion):
  • v = u + at
  • s = ut + ½at²
  • v² = u² + 2as
  • s = ½(u + v)t

Where s = displacement, u = initial velocity, v = final velocity, a = acceleration, t = time. For motion graphs: the gradient of a displacement-time graph gives velocity, and the gradient of a velocity-time graph gives acceleration. The area under a velocity-time graph represents total displacement — a concept that regularly appears in structured Paper 2 questions.

Topic 3: Dynamics

While Kinematics describes how things move, Dynamics explains why they move — it introduces the concept of force and Newton’s three laws of motion. Together, Kinematics and Dynamics make up the core of the Mechanics section, and many O-Level questions combine both topics in a single multi-part question.

Key Definitions

• Force: A push or pull acting upon an object, measured in newtons (N).
• Mass: The amount of matter in an object (kg); a scalar quantity.
• Weight: The gravitational force acting on an object (W = mg); a vector quantity.
• Inertia: The tendency of an object to resist changes to its state of motion; directly related to mass.
• Density: Mass per unit volume (ρ = m/V).
• Moment of a force: Force multiplied by the perpendicular distance from the pivot.

Newton’s Laws and Core Formulas

• Newton’s First Law: An object remains at rest or in uniform motion unless acted upon by a resultant force.
• Newton’s Second Law: F = ma (resultant force = mass × acceleration).
• Newton’s Third Law: For every action, there is an equal and opposite reaction.
• Weight: W = mg (g = 10 N/kg on Earth for O-Level purposes)
• Density: ρ = m / V
• Moment = Force × perpendicular distance from pivot
• Principle of Moments: Sum of clockwise moments = Sum of anticlockwise moments (for equilibrium)

Topic 4: Work, Energy and Power

Energy is one of the most universal concepts in Physics, connecting Mechanics, Thermal Physics and Electricity. Understanding how energy is transferred, stored and converted — and how to calculate the efficiency of those transfers — is essential for answering application-style questions that appear throughout the O-Level papers.

Key Definitions

• Work done: The product of force and displacement in the direction of the force.
• Energy: The capacity to do work, measured in joules (J).
• Power: The rate of work done or energy transferred, measured in watts (W).
• Efficiency: The ratio of useful energy output to total energy input, expressed as a percentage.

Core Formulas

• Work done: W = F × d (where d is displacement in the direction of force)
• Kinetic energy: KE = ½mv²
• Gravitational potential energy: GPE = mgh
• Power: P = W ÷ t = F × v
• Efficiency = (Useful energy output ÷ Total energy input) × 100%

Topic 5: Pressure

The Pressure topic covers how forces are distributed over surfaces and through fluids. It is closely linked to Dynamics and has strong real-world applications — from hydraulic brakes to atmospheric pressure — that examiners frequently draw on for application questions.

Key Definitions and Formulas

• Pressure: Force per unit area, measured in pascals (Pa) or N/m².
• Pressure: P = F ÷ A
• Pressure in a fluid: P = ρgh (where ρ = fluid density, g = gravitational field strength, h = depth)
• Hydraulic systems operate on the principle that pressure is transmitted equally in all directions through a fluid.

Topic 6: Thermal Physics

Thermal Physics covers the kinetic model of matter, how heat is transferred and how substances respond to temperature changes. This topic requires students to think carefully about the behaviour of particles — a skill that bridges neatly into other areas such as gas laws and changes of state.

Key Definitions

• Internal energy: The total kinetic and potential energy of all particles in a substance.
• Specific heat capacity (c): The energy required to raise the temperature of 1 kg of a substance by 1 °C (or 1 K).
• Specific latent heat: The energy required to change the state of 1 kg of a substance without a change in temperature.
• Conduction: Transfer of thermal energy through a material without bulk movement of the material itself.
• Convection: Transfer of thermal energy through bulk movement of a fluid (liquid or gas).
• Radiation: Transfer of thermal energy through electromagnetic waves; does not require a medium.

Core Formulas

• Thermal energy: Q = mcΔT (m = mass, c = specific heat capacity, ΔT = temperature change)
• Latent heat: Q = mL (L = specific latent heat)

Topic 7: Waves, Light and Sound

Waves is a broad topic that covers general wave properties, the behaviour of light, the electromagnetic spectrum and sound. A confident understanding of how waves behave — including reflection, refraction and diffraction — underpins a large portion of the structured questions in Paper 2. Practising ray diagrams alongside the formulas is especially important here.

Key Definitions

• Transverse wave: A wave in which the oscillations are perpendicular to the direction of energy transfer (e.g. light, electromagnetic waves).
• Longitudinal wave: A wave in which oscillations are parallel to the direction of energy transfer (e.g. sound).
• Amplitude: The maximum displacement of a particle from its equilibrium position.
• Frequency (f): The number of complete waves produced per second, measured in hertz (Hz).
• Wavelength (λ): The distance between two successive points in phase on a wave.
• Period (T): The time taken for one complete oscillation.
• Refraction: The change in speed — and direction — of a wave as it crosses a boundary between two different media.
• Critical angle: The angle of incidence at which the angle of refraction equals 90°; above this angle, total internal reflection occurs.

Core Formulas

• Wave speed: v = fλ
• Period and frequency: T = 1 / f
• Snell’s Law: n₁ sin θ₁ = n₂ sin θ₂
• Refractive index: n = sin i / sin r (also n = c / v, where c = speed of light in vacuum)

The electromagnetic spectrum, from longest to shortest wavelength, runs: radio waves → microwaves → infrared → visible light → ultraviolet → X-rays → gamma rays. Students should know the properties and applications of each region, as well as the hazards associated with high-energy radiation.

Topic 8: Electricity and DC Circuits

Electricity is one of the most formula-dense topics in the entire O-Level Physics syllabus and also one of the highest-weighted sections in the examination. Students who invest time understanding the relationships between current, voltage, resistance and power — rather than simply memorising equations — consistently perform better on circuit analysis questions. This topic spans static electricity, current electricity and the analysis of series and parallel circuits.

Key Definitions

• Electric current (I): The rate of flow of charge, measured in amperes (A).
• Potential difference (V): The work done per unit charge between two points in a circuit, measured in volts (V).
• Resistance (R): The opposition to the flow of current, measured in ohms (Ω).
• Electromotive force (e.m.f.): The energy supplied per unit charge by a source such as a battery.
• Ohm’s Law: At constant temperature, the current through a conductor is directly proportional to the potential difference across it (V = IR).

Core Formulas

• Ohm’s Law: V = IR
• Charge: Q = It
• Electrical power: P = IV = I²R = V² / R
• Electrical energy: E = Pt = IVt
• Series circuits: Total resistance R_T = R₁ + R₂ + R₃
• Parallel circuits: 1/R_T = 1/R₁ + 1/R₂ + 1/R₃

In series circuits, current is the same through all components while voltage is shared. In parallel circuits, voltage is the same across all branches while current is shared. These distinctions are critical for circuit analysis problems — one of the most common sources of marks lost in Paper 2.

Topic 9: Magnetism and Electromagnetism

Magnetism and Electromagnetism form a closely linked pair. Once students grasp that changing magnetic fields generate electrical currents — and that electric currents produce magnetic fields — the underlying logic of motors, generators and transformers becomes much more intuitive. These Sec 4 topics carry significant weighting and reward students who can explain physical principles clearly, not just substitute values into formulas.

Key Definitions

• Magnetic field: A region in space where a magnetic force is experienced.
• Electromagnetism: Electric currents create magnetic fields around them; the direction is given by the right-hand grip rule.
• Electromagnetic induction: A changing magnetic field through a conductor induces an electromotive force (Faraday’s Law).
• Transformer: A device that changes AC voltage levels using electromagnetic induction; consists of a primary coil and a secondary coil on a soft iron core.

Core Formulas

• Transformer equation: V_p / V_s = N_p / N_s
• For an ideal transformer: V_p × I_p = V_s × I_s

Topic 10: Radioactivity

Radioactivity was introduced as a standalone topic under the revised O-Level Physics syllabus, covering atomic structure, the nature of radioactive decay, the concept of half-life and the applications and hazards of ionising radiation. It is a relatively self-contained topic that rewards students who are precise with definitions and clear on the properties of each radiation type.

Key Definitions

• Radioactive decay: The spontaneous and random emission of radiation from an unstable nucleus.
• Alpha (α) radiation: Consists of 2 protons and 2 neutrons (a helium nucleus); highly ionising, low penetrating power, stopped by a few centimetres of air or a sheet of paper.
• Beta (β) radiation: A fast-moving electron emitted from the nucleus; moderately ionising, stopped by a few millimetres of aluminium.
• Gamma (γ) radiation: High-energy electromagnetic waves emitted from the nucleus; least ionising but most penetrating, requiring several centimetres of lead or thick concrete to reduce intensity significantly.
• Half-life: The time taken for half the radioactive nuclei in a sample to decay; a fixed value for each isotope regardless of conditions.
• Background radiation: Low-level radiation that is always present from natural and artificial sources; must be accounted for in experimental readings.

Applications of radioactivity include medical imaging, cancer treatment (radiotherapy), carbon dating and smoke detectors. Hazards include ionisation of living cells, DNA damage and increased cancer risk — all of which require appropriate safety measures such as distance, shielding and minimising exposure time.

How to Use These Notes Effectively

Having a comprehensive set of notes is only the first step. The gap between a student who has good notes and a student who scores A1 lies in how actively those notes are used. Here are the habits that make the biggest difference.

• Follow the syllabus sequence. Work through topics in order: Measurement and Mechanics first, then Thermal and Waves, then Electricity and Magnetism, and finally Radioactivity. Each section builds on the previous one.
• Memorise definitions in exact syllabus wording. Examiners award marks for precise language. Paraphrasing a definition that is close but not exact can cost you a mark — and marks add up quickly across Paper 2.
• Write formulas and then apply them immediately. For each formula in these notes, write a practice calculation. Understanding the relationship between variables matters far more than rote memorisation.
• Practise past paper questions by topic. Once you are confident with a topic’s notes, move to topic-specific past paper questions under timed conditions. Track your errors in a dedicated error log to identify recurring weaknesses.
• Balance Paper 1 and Paper 2 practice. Paper 2 structured questions carry the greater share of marks, so prioritise developing your written method and explanation skills — not just MCQ speed.
• Seek feedback on your explanations. Physics answers in Paper 2 often require clear, logical explanations, not just correct calculations. Having a teacher or tutor review your written responses is one of the highest-value investments you can make in your revision.

If you find yourself struggling with certain topics — whether it is interpreting velocity-time graphs, untangling parallel circuits or writing precise definitions for Radioactivity — structured support with a qualified teacher can make an enormous difference. At EduFirst, our Secondary Physics tuition classes are kept deliberately small (just 4 to 8 students per class) so that every student receives targeted attention on their specific gaps. For students who prefer to learn at their own pace or from home, we also offer flexible e-lessons covering the full O-Level syllabus.

Your O-Level Physics Revision Starts Here

O-Level Physics is a subject where consistent, topic-by-topic revision genuinely works. The students who achieve the best results are not necessarily the most naturally talented — they are the ones who build a solid foundation early, revisit their notes regularly and actively test their understanding through practice questions rather than passive re-reading. Use this guide as your go-to reference across all 10 topic areas, return to it as you progress through Sec 3 and Sec 4, and treat it as a living document that you supplement with your own worked examples and error notes over time.

Physics is not about memorising hundreds of isolated facts. It is about understanding patterns, applying precise reasoning and communicating your thinking clearly — skills that take time and the right kind of practice to develop. With the right notes and the right support, every student can make meaningful progress.