Know that for a transverse wave, the direction of vibration is at right angles to the direction of propagation and understand that electromagnetic radiation, water waves and seismic S-waves (secondary) can be modeled as transverse

Published by Patrick Mutisya · 14 days ago

Cambridge IGCSE Physics 0625 – 3.1 General Properties of Waves

3.1 General Properties of Waves

Learning Objective

Know that for a transverse wave, the direction of vibration is at right angles to the direction of propagation and understand that electromagnetic radiation, water waves and seismic S‑waves (secondary) can be modeled as transverse.

What is a Transverse Wave?

A transverse wave is a disturbance in which the particles of the medium (or the fields) oscillate in a direction perpendicular to the direction in which the wave travels. Mathematically, if the wave propagates in the \$+x\$ direction, the displacement \$y\$ of the medium is in the \$y\$‑ or \$z\$‑direction:

\$y(x,t)=A\sin\!\big(kx-\omega t\big)\$

Here \$A\$ is the amplitude, \$k\$ the wave‑number and \$\omega\$ the angular frequency.

Suggested diagram: A side view showing a rope being flicked to illustrate a transverse wave, with arrows indicating the direction of propagation (horizontal) and the direction of vibration (vertical).

Common Transverse Waves

  • Electromagnetic radiation – Light, radio waves, X‑rays etc. The electric and magnetic fields oscillate perpendicular to the direction of travel.

  • Water surface waves – The water particles move up and down while the wave travels horizontally across the surface.

  • Seismic S‑waves (secondary waves) – Shear waves that move through the Earth’s interior, shaking the ground side‑to‑side or up‑and‑down, perpendicular to the direction of propagation.

Comparison: Transverse vs. Longitudinal Waves

FeatureTransverse WaveLongitudinal Wave
Direction of particle vibrationPerpendicular to propagationParallel to propagation
Typical examplesLight, water surface waves, S‑wavesSound in air, compression waves in springs, P‑waves
Medium requirementCan travel in vacuum (e.g., EM waves)Requires a material medium
Particle motionOscillatory up‑and‑down or side‑to‑sideCompressional and rarefaction regions

Key Points to Remember

  1. The vibration direction of a transverse wave is at right angles (90°) to its direction of travel.

  2. Electromagnetic radiation does not need a material medium because the electric and magnetic fields sustain each other.

  3. Water surface waves combine transverse motion (up‑and‑down) with a small longitudinal component, but the dominant motion is transverse.

  4. Seismic S‑waves are the slower of the two main body waves; they cannot travel through fluids because fluids cannot support shear stress.

Common Misconceptions

  • “All waves are the same.” – Waves differ in how particles move; recognising transverse vs. longitudinal is essential.

  • “Light needs air to travel.” – Light is an electromagnetic transverse wave and can propagate through empty space.

  • “Water waves move water particles forward.” – The net motion of water particles is very small; they mainly move up and down as the wave passes.

Questions for Practice

  1. Identify whether each of the following phenomena is a transverse or longitudinal wave: (a) a guitar string vibrating, (b) a sound wave in air, (c) a radio broadcast, (d) a ripple on a pond.

  2. Explain why seismic S‑waves cannot travel through the Earth’s outer core.

  3. Draw a labelled sketch (see suggested diagram) of a transverse wave on a rope, indicating the direction of propagation and the direction of particle vibration.