C.3.1—Wavefronts and rays
- Syllabus
- First assessment 2025
- Objective
- —
- Level
- HL
Model Wavefronts and Rays
Define a wavefront
A wavefront is a line or surface joining points that are in phase. Adjacent wavefronts are separated by one wavelength. In a uniform medium, the wavefronts are perpendicular to the direction of propagation.
Use rays to show propagation
A ray is a line showing the direction in which the wave transfers energy. Draw rays perpendicular to the local wavefronts; straight, parallel wavefronts give parallel rays, while circular wavefronts from a point source give radial rays.
Read the geometry
When a wavefront diagram changes direction at a boundary, compare the ray direction and the spacing of wavefronts on each side. The wavefront construction helps distinguish a change in speed from a change in frequency.
Common trap
Do not draw rays parallel to wavefronts. A ray follows energy propagation and is normal to the wavefront at each point.
C.3.1 Exam Analysis
[ 3 ]
Sketch two appropriate rays on the diagram to show the formation of the image. Label the image with the letter I.
Drawing canvas
Retrieve the Core C.3 Wave Phenomena Model
C.3 Wave phenomena is secure when you can connect the physical picture to the equation and its limits.
- Wavefronts and rays
- Reflection, refraction and Snell’s law
- Refractive index and total internal reflection
- Superposition, coherent sources and interference
- Young’s double-slit pattern