O-Level Physics 6091 Definitions + Formulae List (2026): Topic-by-Topic Recall Sheet

Q: What does SEAB O-Level Physics (6091, 2026): The Definitions & Formulae Guide cover?
A: A syllabus-faithful, exam-ready list of definitions and relationships explicitly required in Singapore's O-Level Physics (6091, 2026), plus clarifications on common extras.

TL;DR This is a recall sheet, not a full lesson. Use it to check whether you can state each definition and write each required relationship quickly. For each formula, learn the quantity meaning, unit, and graph link instead of memorising symbols alone. If a relationship is not explicitly assessed as a recall/apply formula, this guide labels it so you do not over-memorise.

This post distills the main definitions and formulae that the SEAB O-Level Physics (6091, 2026 syllabus) explicitly expects you to know and apply. Where a concept is commonly taught but not printed as a “recall/apply” relationship in the syllabus, I label it accordingly so you don't memorise more than you need.

For 2027, SEAB lists SEC G3 Physics K323 with 6091 as its reference code. When we compared the 6091 (2026) and K323 (2027) PDFs word by word on 23 October 2026, we found no difference in content. If you are sitting SEC G3 Physics in 2027, use this page alongside the K323 PDF.

Quick recall map

Formula-to-meaning checkpoint

Use this four-part check before treating a formula as memorised. It keeps recall tied to the physics, not just to symbol matching.

Worked check: for $p = F/A$, do not only say "pressure equals force divided by area". A stronger recall sentence is: pressure is force per unit area; force is measured in newtons, area in square metres, and pressure in pascals; if the same force acts over a smaller contact area, pressure increases.

Misconception check: a definition is not just the formula written in words. It should name the physical idea that the formula is measuring.

Concrete example: speed is not just a formula

Weak recall:

Speed equals distance divided by time.

Better recall:

Speed is the rate of change of distance. Its SI unit is metre per second. On a distance-time graph, the gradient gives speed.

The second version is exam-safer because it links the definition, unit, and graph interpretation in one answer.

Stay Connected

Use our O-Level Physics Experiments hub to keep formula drills synced with the hands-on investigations you'll meet in Paper 3.

At-a-glance formula sheet

Units are SI unless stated. Use the value of $\pu{g}$ given in the question. If none is given, follow your school’s convention (many schools use $\pu{g = 10 m s-2}$ for simpler arithmetic; some use $\pu{g = 9.81 m s-2}$).

Measurement & basics

• No explicit equations beyond rearrangement and graphing in the form $y=mx+c$.

Kinematics

• Average speed: $\bar{v} = \dfrac{\text{distance}}{\text{time}}$
• Acceleration: $a = \dfrac{\Delta v}{\Delta t}$
• Graph facts: area under a velocity-time graph = displacement; gradient of a velocity-time graph = acceleration.

Dynamics

• Weight: $W = mg$
• Resultant force (Newton's 2nd law form): $F = ma$

Turning effects

• Moment (torque): $\tau = F d_{\perp}$ (perpendicular distance to pivot)
• Principle of moments (equilibrium): sum of clockwise moments $=$ sum of anticlockwise moments

Pressure & density

• Pressure (mechanical): $p = \dfrac{F}{A}$
• Density: $\rho = \dfrac{m}{V}$
• Hydrostatic pressure: $p = h \rho g$

Energy, work & power

• Work done: $W = F s$ $force \times displacement along the line of action$
• Kinetic energy: $E_k = \dfrac12 m v^2$
• Gravitational potential energy (near Earth): $E_p = mgh$
• Power: $P = \dfrac{E}{t}$
• Efficiency: $\text{efficiency} = \dfrac{\text{useful output}}{\text{total input}}$

Thermal physics

• Specific heat capacity: $Q = mc \Delta T$
• Specific latent heat: $Q = mL$

Waves

• Wave speed: $v = f \lambda$

Light

• Reflection: angle of incidence $=$ angle of reflection
• Refraction (Snell's-law form in 6091): $\dfrac{\sin i}{\sin r} = \text{constant}$
• Refractive index (definition-based): $n = \dfrac{c}{v}$ (speed in vacuum over speed in medium)

Electricity (current & circuits)

• Charge: $Q = It$
• Resistance (defining relation): $R = \dfrac{V}{I}$
• Series circuits: $R_\text{series} = R_1 + R_2 + \cdots$
• Parallel circuits: $\dfrac{1}{R_\text{parallel}} = \dfrac{1}{R_1} + \dfrac{1}{R_2} + \cdots$

Practical electricity

• Electrical power: $P = VI$
• Electrical energy (constant $V$ and $I$): $E = V I t$
• Billing (kWh): $E(\text{kWh}) = P(\text{kW}) \times t(\text{h})$
• Cost = energy (kWh) x tariff

Magnetism & electromagnetism

• No new equations (qualitative field patterns, force directions, etc.)

Electromagnetic induction

• Ideal transformer: $\dfrac{V_p}{V_s} = \dfrac{N_p}{N_s}$, $V_p I_p = V_s I_s$ (assuming 100% efficiency)

Radioactivity

• Nuclide bookkeeping: use and balance $^{A}_{Z}X$ in decay equations (see below)
• Half-life: simple calculations from tables/graphs (exponential law not required)

Definitions you should be able to state

Measurement

• Physical quantity: has a numerical magnitude and a unit.
• Scalar vs vector: scalars have magnitude only; vectors have magnitude and direction.
• Base SI quantities/units and SI prefixes ($k, M, m, \mu,$ etc.).

Kinematics

• Speed vs velocity: rate of change of distance vs rate of change of displacement.
• Uniform acceleration: constant rate of change of velocity.
• Displacement (concept; graph interpretation required).

Dynamics

• Mass: amount of matter (and measure of inertia).
• Inertia: resistance to change of motion.
• Gravitational field: region where a mass experiences gravitational force.
• Gravitational field strength (g): force per unit mass at a point.
• Terminal velocity: fall with air resistance reaches a constant speed when resistive force balances weight.

Turning effects

• Moment of a force and centre of gravity (weight acts as if at a point).

Pressure & density

• Pressure and density as above (with units).

Energy, work & power

• Conservation of energy.
• Work, power, efficiency (as in formulae).

Thermal physics

• Heat capacity and specific heat capacity.
• Latent heat and specific latent heat.
• Internal energy: store comprising total random kinetic energy of particles + total inter-particle potential energy.

Waves

• Amplitude, period, frequency, wavelength, wave speed (graphical identification & use).

Light

• Refractive index $n = \dfrac{c}{v}$.
• Critical angle and total internal reflection (concepts).
• Image characteristics for a thin converging lens: real/virtual, upright/inverted, magnified/diminished; draw and interpret ray diagrams.
• Focal length of a converging lens (concept/use).

Electricity

• Electric field: region where a charge experiences a force.
• Current: rate of flow of charge $A$.
• Electromotive force (e.m.f.): work done per unit charge by the source around a complete circuit $V$.
• Potential difference (p.d.): work done per unit charge across a component $V$.

Practical electricity (safety)

• Live, neutral, earth (ground) wires: meanings and roles.
• Mains plug wiring; switches/fuses on the live wire; earthing and double insulation.

Magnetism & electromagnetism

• Magnetic field (field lines and patterns around magnets, straight conductors, and solenoids).

Electromagnetic induction

• Qualitative induction (what changes increase induced e.m.f., sketching AC output).
• (Mnemonic names like “Fleming's right-hand rule” are not required by the spec, though left-hand rule is commonly discussed for motors.)

Radioactivity

• Nuclide notation $^{A}_{Z}X$ (interpret $A, Z$).
• Alpha, beta, gamma: nature and effects on $A$ and $Z$.
• Half-life (meaning and use in simple calculations).
• Nuclear fission and fusion (meanings).
• Activity $A$ (symbol/unit recognition; formal $A=\lambda N$ not required).

Practice Quiz

Check your memory of must-know definitions and equations-while spotting the "common extras" you can deprioritise.

Worked “formats” you will actually use

1) Hydraulics / fluids

• $p = \dfrac{F}{A}$ and $p = h\rho g$ appear often in connected-container or manometer contexts.

2) Energy chains & power

• Combine $P=VI$ with $E=VIt$ to move between power, current, voltage, time, and energy.
• Billing: convert W ↔ kW and s ↔ h cleanly before multiplying by the tariff.

3) Graphing to linear form

• Many lab relationships need rearrangement to $y=mx+c$ so that the gradient/intercept equals a physical constant. Label axes with units and propagate uncertainties sensibly.

4) Lens work

• Use ray diagrams for object $>f$, $=f$, and $<f$. Quote image properties rather than plugging a magnification formula (not required).

5) Radioactive decay questions

• Balance nuclide equations for $\alpha$ and $\beta$ ($\beta^-)$ increases $Z$ by $1$, $A$ unchanged; $\alpha$ decreases $A$ by $4$ and $Z$ by $2$; $\gamma$ leaves $A, Z$ unchanged.
• Half-life: read off from tables/curves or apply stepwise halving; avoid introducing $\lambda$ unless given.

Easy-to-miss items that are in 6091

These are part of 6091 and worth putting on your sheet:

• Internal energy (definition).
• Terminal velocity (concept under motion with air resistance).
• Electrical energy & cost in kWh (plus $P=VI$, $E=VIt$).
• Mains wiring & safety: live/neutral/earth, earthing, double insulation, switches/fuses on live.
• Electrostatic charge transfer (rubbing, induction, hazards).
• Image characteristics vocabulary (real/virtual, magnified/diminished, upright/inverted).
• Nuclide equations for $\alpha$, $\beta$, $\gamma$ and half-life calculations.

Commonly taught but not printed as recallable relations in 6091

You may still learn/use these in class, but they're not listed as formulae to memorise in this syllabus:

• $f = \dfrac{1}{T}$ (frequency-period)
• Critical angle formula: $\sin c = \dfrac{1}{n}$
• Magnification and thin-lens equation $\dfrac{1}{f} = \dfrac{1}{u} + \dfrac{1}{v}$
• Average velocity = displacement/time (only average speed is printed)
• Resistivity $R=\rho \dfrac{\ell}{A}$
• Radioactive decay law $N=N_0 \left(\dfrac12\right)^{t/T_{1/2}}$ and $A=\lambda N$
• Named mnemonics like right-hand grip and Fleming's right-hand rule (qualitative ideas are examined, but the mnemonics themselves aren't specified)

Final notes

• Stick to SI units and clear significant figures.
• When in doubt, draw the diagram (free-body, ray, circuit, field lines) and map each quantity to the appropriate relationship.
• The syllabus emphasises interpretation of graphs, proportional reasoning, and linking concepts (e.g., energy → power → cost), as much as raw formula recall.