Ray optics is a powerful approximation—when it applies.

In geometrical optics, light is represented by rays that indicate direction of propagation. The model is highly effective when wavelength is small compared to objects and apertures.

• Rays as direction markers
• Wavefront intuition (conceptual)
• When “straight-line” propagation holds
• What the model does not capture

Reflection and refraction describe how rays change direction at boundaries. The key is careful geometry: angles are measured from the normal.

• Normal line and angle definitions
• Reflection as symmetry about the normal
• Refraction as direction change in a new medium
• Qualitative “bend toward/away” reasoning

Ray optics fails when wavelength-scale effects matter. Diffraction and interference reveal the wave nature of light and set limits on resolution and shadow sharpness.

• Why wavelength matters
• Diffraction as “spreading” at edges
• Interference patterns vs ray predictions
• What to expect near small apertures

Practice drawing rays, identifying normals, and deciding whether the ray model is appropriate for a situation.

• Ray-diagram interpretation drills
• Reflection vs refraction identification
• Angle-from-normal practice
• When does ray optics fail? concept checks
• Exam-style geometrical optics sets