Progressive, transverse & longitudinal waves
A wave lets energy travel from one place to another without carrying the medium along with it. In this AS-level lesson we build the whole language of waves from the ground up: what wave motion really means, the quantities displacement, amplitude, wavelength, period and frequency, and the two graphs the examiner loves — displacement–distance and displacement–time. We define phase and phase difference in degrees and radians, derive the wave equation v = fλ from first principles (with f = 1/T), meet intensity as power per unit area with I ∝ A², and finally sort every wave into two great families — transverse (oscillations perpendicular to travel) and longitudinal (oscillations parallel to travel, with compressions and rarefactions).
By the end you should be able to (NSSCAS Physics (AS) 2.1):
- Describe wave motion as an oscillation that transfers energy from one place to another without any net movement of the medium, as shown by ropes, springs and water waves
- Describe and use the terms displacement, amplitude, phase difference, period, frequency, wavelength and speed
- Analyse and interpret displacement–distance and displacement–time graphs of a wave
- Recall and use phase difference measured in degrees and radians (in phase, antiphase)
- Derive, from the definitions of speed, frequency and wavelength, the wave equation v = fλ, and recall and use v = fλ and f = 1/T
- Describe that energy is transferred by a progressive wave, and recall and use intensity = power ÷ area with intensity ∝ (amplitude)²
- Compare transverse and longitudinal waves (oscillations perpendicular versus parallel to the direction of energy travel), with examples such as light and sound