Ch 1 · General Properties of Waves · IGCSE Physics 0625
Topic 1 of 3 in Waves — IGCSE Physics 0625 — 19 lessons.
Introduction
Light from the Sun, sound from a speaker, ripples on a pond and the tremors of an earthquake are all waves. They look very different, but they share the same vocabulary and obey the same equation, v = fλ. This lesson sets up the language of waves that you will use again for light, sound and the electromagnetic spectrum.
Key ideas
1. Waves transfer energy, not matter. A wave carries energy (and information) from one place to another, but the material it travels through does not travel with it. A cork on a pond bobs up and down as ripples pass; it does not move along with them.
🧑🏫 Teacher's explanation
Imagine you are standing in a crowded stadium and perform 'The Wave'. You stand up and sit down, and the movement travels around the stadium. However, you haven't moved from your seat; you've only moved up and down. This is exactly how a wave works: it transfers energy (the 'wave' motion) through a medium, but the particles (the people) stay in their original positions.
📖 Definitions
🔍 Worked example — Easy
A water wave has a frequency of 5 Hz and a wavelength of 0.4 m. Calculate the speed of the wave.
🔍 Worked example — Standard
A sound wave travels at 340 m/s with a frequency of 680 Hz. Calculate its wavelength.
⚠️ Common errors
🧠 Quick check 1
🧠 Quick check 2
🎯 Exam question
Practical notes
Worked example
Example 1 — water waves. A ripple tank vibrator produces waves of frequency 12 Hz. Ten complete wavelengths span 15 cm. Calculate the wave speed.
🔍 Worked example — Easy
A ripple tank vibrator produces waves of frequency 12 Hz. Ten complete wavelengths span 15 cm. Calculate the wave speed in m/s.
🔍 Worked example — Standard
Waves of wavelength 2.0 cm travel at 0.30 m/s in deep water. They pass into shallow water, where their speed is 0.18 m/s. Find the frequency and the new wavelength in the shallow water.
🔍 Worked example — Exam-style
A seismic wave travels through rock at 6.0 km/s with a frequency of 2.0 Hz. Find its wavelength in km.
⚠️ Common errors
Common mistakes and examiner tips
Practice
Answers: (1)(a) The maximum displacement of the wave from its rest position; (b) the number of complete waves passing a point per second. (2) λ = v/f = 340/512 = 0.664\ m ≈ 0.66\ m. (3) Transverse: light, water ripples, S-waves. Longitudinal: sound, P-waves. (4) 45/3 = 15\ cm. (5) λ = 3.0 × 10^8/98 × 10^6 = 3.1\ m. (6) Speed decreases, wavelength decreases, frequency stays the same, and the direction changes (the waves bend towards the normal). (7) Make the gap narrower (closer to the wavelength) or increase the wavelength of the waves. (8) Sound has a wavelength similar to the width of the doorway, so it diffracts strongly round the edges; light has a wavelength far smaller than the doorway, so it hardly diffracts and travels in straight lines.