Follow light from a source to a surface and then to an observer. Explain what different materials do to the light.
Reflection notes include light and materials.
In a uniform transparent medium, the geometric ray model uses straight paths. Arrowheads show travel direction. A diagram includes selected rays, not every ray leaving a source. Use a ruler for straight segments and label the source, surface and observer.
Transparent materials transmit light with little scattering, so objects can be seen clearly through them. Translucent materials transmit light but scatter it enough to blur the view. Opaque materials transmit little or no visible light through the sample. Thickness and wavelength can matter.
A glass window can transmit much of the light while reflecting some. A coloured surface absorbs some wavelengths more strongly than others. Absorption often transfers energy into thermal energy. Avoid assigning every object exactly one behaviour.
A smooth surface can preserve a coherent reflected image. On a rough surface, different small patches have different normals, scattering reflected light in many directions. The law of reflection still applies locally. A shadow forms where an object blocks light from reaching a region; an extended source can create a partial shadow.
Use directional ray diagrams to distinguish transmission, absorption, regular reflection and diffuse reflection.
TED-Ed · Animation
Connect transmission with the material’s response to visible light. The microscopic explanation is an extension of the ray model.
Drag the blocker toward the light or the screen. Then widen the light source to investigate a softer edge.
Straight-ray model of an opaque blocker and a uniform vertical light source. Brightness is schematic; this does not model scattering or inverse-square dimming.
A material transmits light but blurs the view. State transparent, translucent or opaque and explain your reasoning.
Separate light passing through from image clarity.
Translucent materials transmit and scatter light.
Does diffuse reflection still obey the local law of reflection? State yes or no and explain your reasoning.
Think about each small surface patch.
Each patch has a normal; the reflected angle equals the incident angle at that patch.
Would adding more frosting make a window luminous? Explain.
No. Scattering changes directions of incoming light. It does not turn the window into a source of visible light.
If it reflected no visible light, it would appear very dark under illumination. Matte surfaces usually scatter reflected light rather than forming a sharp mirror image.
Commit to an answer, then use the feedback to check your reasoning.
