Sound is a longitudinal wave. Explain how it travels through air, with a diagram of compressions and rarefactions.
How to lay out the answer. Follow the frame, then write it in your own words.
1 · Define. A longitudinal wave is one in which the particles of the medium vibrate parallel to the direction of the wave.
2 · Explain the travel.
A vibrating source (tuning fork) pushes the air forward: a compression forms.
It moves back and the air spreads out: a rarefaction forms.
These move outward; the particles only vibrate about their places while energy travels.
3 · Draw. [Diagram: tuning fork with alternate crowded (C) and spread-out (R) bands of dots; wavelength λ marked between two compressions; arrow for the direction of travel]
4 · Write v = nλ. Speed = frequency × wavelength.
5 · Real-life link. The sound of a temple bell reaches you as compressions and rarefactions in the air.
6 · Close. So sound needs a medium and travels as a longitudinal wave.
Scoring tip: Mark C and R clearly and show λ between two compressions: the labelled diagram carries the marks.
