C.2
Wave Model
Transverse and longitudinal waves, wave properties, the wave equation and a comparison of sound and electromagnetic waves.
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Key Concepts, Wave Model
Transverse and Longitudinal Waves
In a transverse wave, the particles of the medium oscillate perpendicular to the direction of wave travel. Light, water ripples and waves on a string are transverse. In a longitudinal wave, the particles oscillate parallel to the direction of wave travel, creating alternating regions of compression (high pressure) and rarefaction (low pressure). Sound is the most important example of a longitudinal wave. All waves transfer energy without transferring matter: the particles oscillate about their equilibrium positions but do not travel with the wave.
Wave Properties and Definitions
Wavelength λ is the distance between two adjacent points in phase (e.g. two crests or two compressions), measured in metres. Amplitude A is the maximum displacement of a particle from its equilibrium position. Frequency f is the number of complete oscillations per second, measured in hertz (Hz). Time period T = 1/f is the time for one complete oscillation. Wave speed v is the distance travelled by the wave per second, in m/s. These five quantities are connected by the wave equation v = fλ, which is derived from the fact that in one period, the wave advances exactly one wavelength.
The Wave Equation
The wave equation v = fλ can be derived from the definitions of speed, frequency and wavelength. In one period T, the wave moves forward exactly one wavelength λ. Since speed = distance/time, we get v = λ/T = λ × f, giving v = fλ. This equation applies to all waves. Note that wave speed is a property of the medium through which the wave travels (for a given type of wave and medium), not of the source. Changing the source frequency changes the wavelength but not the wave speed: higher frequency means shorter wavelength.
Sound Waves vs Electromagnetic Waves
Sound waves are longitudinal mechanical waves: they require a medium to travel through and cannot travel through a vacuum. They travel at approximately 340 m/s in air at room temperature, faster in liquids and solids. Electromagnetic (EM) waves are transverse and do not require a medium: they travel through a vacuum at c = 3 × 10⁸ m/s. The EM spectrum includes (from longest to shortest wavelength): radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays. All EM waves travel at the same speed in a vacuum but slow down when passing through a material medium, which is the cause of refraction.
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Frequently Asked Questions, IB Physics Wave Model
What is Wave Model in IB Physics? ↓
Transverse and longitudinal waves, wave properties, the wave equation and a comparison of sound and electromagnetic waves. This topic is part of Theme C (Wave Behaviour) in the current IB Physics syllabus.
Is Wave Model SL or HL in IB Physics? ↓
Wave Model is covered by both SL and HL students in the current IB Physics syllabus. HL students study additional depth and extension content beyond the SL core.
What equations do I need for IB Physics Wave Model? ↓
The key equations for Wave Model are covered in the concept tutorial above. For a structured set of notes with all equations, conditions and worked examples, the GradePod Exam Pack includes a revision note template for every topic.
What are common exam mistakes in IB Physics Wave Model? ↓
Common mistakes are covered in detail in the exam technique video above. The GradePod Exam Pack also includes exam-style questions with mark schemes so you can see exactly how marks are awarded and where students typically drop them.
How do I revise Wave Model for the IB Physics exam? ↓
Follow the GradePod three-step method. First, watch the concept tutorial and tick off each learning objective on the checklist above as you go. Second, watch the exam technique video to see how IB-style questions are answered under exam conditions. Third, use the Exam Pack to practise independently with knowledge questions, exam questions and mark schemes. That's it. It works. I promise.