Waves: Revision Notes (Form 4 SPM Physics)

What this chapter covers

• 5.1 Fundamentals of Waves
• 5.2 Damping and Resonance
• 5.3 Reflection of Waves
• 5.4 Refraction of Waves
• 5.5 Diffraction of Waves
• 5.6 Interference of Waves
• 5.7 Electromagnetic Waves

Key ideas explained

• How noise-cancelling headphones work, The headphones produce a sound wave that is the exact opposite of the incoming noise. Where a crest meets a trough, the two cancel by destructive interference and the noise fades.
• Why we can hear around corners, Sound waves spread out as they pass through openings and edges, an effect called diffraction. Because their wavelength is large, they bend around corners so you hear before you see.
• What resonance is, Resonance is when something is pushed at its own natural frequency, so each push adds to the last and the vibration grows large. A playground swing is the clearest example.

Formulas to memorise (none are given in the exam)

• v = fλ, Wave speed, v = wave speed (m s⁻¹); f = frequency (Hz); λ = wavelength (m)
• T = 1 / f, Period and frequency, T = period (s); f = frequency (Hz)
• λ = ax / D, Interference of waves, λ = wavelength (m); a = slit separation (m); x = fringe separation (m); D = distance from slits to screen (m)

Terms you must define precisely

• Refraction of waves, The change in direction of a wave as it passes from one medium to another because of a change in its speed.
• Diffraction, The spreading of waves as they pass through a gap or around the edge of an obstacle.
• Interference, The superposition of two waves of the same type, producing regions of reinforcement (constructive) and cancellation (destructive).
• Resonance, The large-amplitude vibration that occurs when a system is driven at its own natural frequency.
• Electromagnetic spectrum, The full range of electromagnetic waves arranged by frequency or wavelength, from radio waves to gamma rays, all travelling at the speed of light in a vacuum.
• Wave, A disturbance that transfers energy from one point to another without transferring matter.
• Transverse wave, A wave in which the particles of the medium vibrate at right angles to the direction the wave travels, such as water waves and light.
• Longitudinal wave, A wave in which the particles of the medium vibrate parallel to the direction the wave travels, such as sound waves.

A revision order that works

1. Finish with a timed set of calculations with units on every line.
2. Read the 7 standards above and tick the ones you can already explain aloud without notes.
3. Rewrite every definition in one sentence with the correct unit; definitions are the cheapest marks in Paper 2.
4. Derive each formula once from its meaning, then practise rearranging it before substituting numbers.
5. For each experiment, write the manipulated, responding and constant variables from memory, then the graph you would plot.

More Waves resources

• Chapter overview: Waves
• Common Mistakes
• Practice Questions
• Paper 2 Answering Guide
• Paper 3 Guide
• Key Terms
• Calculation practice sets

Source: DSKP KSSM Physics Form 4 and 5 (Versi English), Sijil Pelajaran Malaysia: Format Pentaksiran mulai 2021, Fizik (4531) (Bahagian Pembangunan Kurikulum (BPK), KPM)