Begin by identifying the fundamental idea that controls the situation.
Examples include:
Conservation of Energy
Newton's Second Law
Newton's Third Law
Conservation of Momentum
Circular Motion
Electromagnetic Induction
Wave Superposition
Avoid starting with equations.
Instead of writing (F = ma), write:
According to Newton's Second Law, the resultant force determines the object's acceleration.
The principle tells the examiner what idea you are about to apply.
Now connect the physics to the question.
Instead of stating a general fact, explain how it applies here.
For example:
❌ Energy is conserved.
✅ Since friction is negligible, no mechanical energy is lost, so gravitational potential energy is converted into kinetic energy.
Notice that the second sentence explains why energy is conserved.
Ask yourself: So what? What does the principle predict?
Examples:
Therefore, the ball accelerates.
Therefore, the current increases.
Therefore, the magnetic field weakens.
Therefore, the object reaches the same height.
Therefore, the wave undergoes destructive interference'
Every statement should naturally follow from the previous one.
Equations should support an explanation—not replace it.
Poor example:
Better example:
Since mechanical energy is conserved,
Therefore, increasing the release height increases the speed at the bottom of the track.
The equation is evidence for the conclusion.
Always answer the original question.
Examples:
Therefore, the ball completes the loop.
Therefore, the induced current decreases.
Therefore, the collision is elastic.
Therefore, the image is virtual and magnified.
Don't leave the examiner to infer your conclusion.
Physics Principle
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Apply it to this situation
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Explain the physical consequence
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Support with equations (if appropriate)
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State the final conclusion
Be well prepared for the following physics ideas and questions. You should be able to discuss each one orally and then explain it clearly in writing. Use diagrams, graphs, visual aids, or equipment to support your explanations.
Newton's Laws in System: State Newton’s three laws of motion and analyse how they apply to a complex physical system (e.g., rocket propulsion or connected masses), explicitly detailing force interactions, frames of reference, and momentum changes
Gravitational Fields: Why does an apple fall? Using Newton’s Law of Universal Gravitation and field theory, explain why objects accelerate toward Earth. Discuss the relationship between mass, gravitational field strength (g), and gravitational force (Fg).
Conservation of Energy: Why is there no such thing as a free lunch? Explain the Law of Conservation of Energy and the principle of thermal/mechanical efficiency. Discuss why energy transformations can never exceed 100% efficiency and why perpetual motion machines are physically impossible.
Momentum vs. Impulse: Distinguish between linear momentum and impulse using Newton’s Second Law (∆p = F ∙ ∆t). Explain how manipulating contact time impacts peak force in real-world collision dynamics.
Centripetal vs. "Centrifugal" Force: Distinguish between centripetal force and 'centrifugal force'. Explain why centripetal force is a necessary real force for circular motion, whereas 'centrifugal force' is an apparent/fictitious effect arising in a non-inertial rotating frame of reference
Geostationary Satellites: Explain the physical conditions required for a satellite to achieve a geostationary orbit. Derive an expression for its orbital radius using Newton’s Law of Universal Gravitation and principles of circular motion, and explain why a geostationary satellite must orbit directly above the equator.
Simple Harmonic Motion (SHM): Define Simple Harmonic Motion (SHM) in terms of acceleration and displacement (a = -ω^2 ∙ x). Explain the criteria required for a system to exhibit SHM, and analyse the continuous exchange of energy between kinetic and potential energy throughout one complete oscillation.
Doppler effect: Explain the Doppler effect for sound when there is a moving source, a moving listener, or a listener positioned at an angle relative to the source.
Diffraction: What is wave diffraction, and how does it occur around barriers? Is diffraction more pronounced when passing through a small opening or a large opening?
Thomas Young's Double-Slit Experiment: Explain what Thomas Young demonstrated in his double-slit experiment and how his results supported the wave theory of light.
Thin-Film Interference: Explain the physical mechanism behind the colourful patterns observed in a soap bubble or a thin layer of petrol on water.
Transverse vs. Longitudinal Waves (Polarisation): Identify and explain the wave phenomenon that distinguishes transverse waves from longitudinal waves.
Standing Waves: Explain how standing waves are formed in musical instruments and how they determine the pitch produced.
Electromagnetic Induction & Power Generation: Explain the physical principles of electromagnetic induction that govern large-scale electrical power generation. Detail how Faraday’s Law and Lenz’s Law explain the creation of an induced electromotive force (EMF) when relative motion occurs between a magnetic field and a conductor.
AC vs. DC and Power Distribution: Distinguish between Alternating Current (AC) and Direct Current (DC). Explain why AC is used for national power grid distribution, analysing how transformers utilise changing magnetic flux to step up voltage and minimise resistive transmission losses (P_loss = I^2 ∙ R).
Ohm's Law & Conduction Mechanisms: State Ohm’s Law and specify the environmental conditions under which it holds. Compare the current-voltage (I-V) characteristics of an Ohmic conductor, a filament lamp, and a semiconductor diode, explaining the microscopic mechanism (e.g., thermal lattice vibrations) causing non-ohmic behaviour.
The Nature of Light: Explain the physical nature of light, addressing both its wave-like and particle-like properties.
The Bohr Model: Describe the key postulates of the Bohr model of the hydrogen atom and explain how it accounts for atomic emission spectra
Atomic Structure & Line Spectra: Explain how the quantisation of atomic energy levels gives rise to both emission and absorption line spectra. In your response, detail the mechanisms of electron excitation, photon emission/absorption, and ionisation.
Photoelectric Effect: Explain the photoelectric effect and analyse why classical wave theory fails to account for experimental observations such as threshold frequency, immediate emission, and stopping voltage. Explain how Einstein's photon model resolves these contradictions
Fusion vs. Fission: Compare and contrast nuclear fission and nuclear fusion. Use the binding energy per nucleon curve and mass defect principles to account for the energy released in both processes.
Mass Deficit & Binding Energy: Define mass deficit and binding energy. Explain how the conservation of mass-energy (E = mc^2) is applied to calculate the net energy absorbed or released during nuclear transformations.
Mass-Energy Equivalence: Explain the physical significance of mass-energy equivalence (E = mc^2) and describe how mass defect manifests as kinetic energy or radiation in nuclear reactions
Wave-Particle Duality: Discuss the concept of wave-particle duality for both light and matter. Cite experimental evidence supporting both behaviours (e.g., diffraction vs. photoelectric effect) and explain how the de Broglie wavelength determines when wave properties dominate
Nuclear Forces & Stability: Analyse the interplay between the strong nuclear force and Coulombic repulsion within the nucleus. Explain how this balance dictates nuclear stability and why heavier nuclei require a higher neutron-to-proton ratio.