IB Physics: Wave Characteristics FAQ

Start by identifying exactly which property is being asked about — wavelength, frequency, amplitude, period or speed — then quote the correct equation before substituting numbers. Examiners award marks for stating relationships (like v = fλ) explicitly, not just for a final number pulled from a calculator.

The IB Physics guide requires you to know wavelength, frequency, period, amplitude, wave speed and phase difference, plus the distinction between transverse and longitudinal waves. Displacement-distance and displacement-time graphs are used to extract these, and you're expected to read both accurately.

In a transverse wave the particle oscillation is perpendicular to the direction of energy transfer — light and all electromagnetic waves work this way. In a longitudinal wave, like sound, particles oscillate parallel to the direction of travel, creating compressions and rarefactions instead of crests and troughs.

Wave speed is calculated using v = fλ, where f is frequency in hertz and λ is wavelength in metres. For waves on a string or in a medium, you can also use v = distance ÷ time if you're given how far a wavefront travels in a measured time interval.

According to the IB Physics guide with first assessments in 2025, wave characteristics falls under Theme C: Wave Behaviour, specifically sub-topic C.2 The Wave Model. This links directly into C.1 Simple Harmonic Motion and C.3 Wave Phenomena, so questions often blend all three.

SL students cover wave characteristics, wave behaviour (reflection, refraction, diffraction, superposition) and standing waves. HL students go further into Doppler effect calculations, resolution and diffraction gratings, plus deeper mathematical treatment of two-source interference — all assessed with harder multi-step Paper 2 questions.

Expect "define" for terms like amplitude or period, "state" for a quick fact with no working needed, "determine" when a calculation is required, "sketch" for graphs with key features but not precise plotting, and "explain" when you need to link cause to effect using physics reasoning.

Wave characteristics appears across all three papers. Paper 1 uses multiple-choice questions on definitions and quick calculations, Paper 2 has longer structured questions combining wave speed, graphs and real contexts, and Paper 3 can bring in wave behaviour through experimental data analysis, especially for HL.

The biggest one is confusing wavelength and period on graphs — both look like "the gap between two peaks," but one is measured in metres from a distance graph and the other in seconds from a time graph. The second biggest is forgetting units when quoting frequency in kHz or MHz.

Drill past paper Paper 2 questions specifically on graph interpretation — that's where marks disappear fastest. I've marked hundreds of scripts where students knew the equations perfectly but lost 2-3 marks per question misreading a displacement graph under time pressure.

It's not conceptually harder than mechanics, but it's more graph-heavy, and that trips up students who are strong with equations but weaker at reading data visually. Once you can confidently distinguish displacement-distance from displacement-time graphs, most of the topic's difficulty disappears.

Struggling with one sub-topic mid-course isn't a reliable signal to switch levels — waves is graph-heavy and catches out even strong students initially. I'd look at their overall trend across mechanics, waves and thermal physics together before making a level decision, ideally with input from their class teacher.

Focus on resources that isolate graph-reading practice rather than generic definition lists, since that's where most marks are actually lost. On RevisionPrep, the Topical Worksheets for wave behaviour pair calculation questions with graph-based ones, and the Revision Notes summarise the exact command-term expectations examiners use.