Reflection is the process where a wave strikes a boundary and bounces back into the medium from which it originated. This interaction occurs at the interface and does not involve the wave passing through the bulk of the second material.
Absorption occurs when the energy of the incident wave is taken up by the matter in the second medium, typically being converted into internal energy such as heat. This process reduces the intensity of the wave as it travels through or interacts with the material.
Transmission refers to the passage of wave energy through a medium or across a boundary into a new medium. If the wave enters the new medium at an angle and the wave speed changes, this often results in refraction, or the bending of the wave path.
Conservation of Energy dictates that the total incident intensity () must equal the sum of the reflected (), absorbed (), and transmitted () intensities. This is expressed by the fundamental relationship:
Transparent materials allow light to pass through them with minimal scattering, enabling objects on the other side to be seen clearly. In these materials, the majority of the incident energy is transmitted rather than reflected or absorbed.
Translucent materials transmit light but scatter it in the process, which prevents the formation of clear images. This occurs because the internal structure of the material causes the light rays to change direction multiple times before exiting.
Refraction often accompanies transmission when light moves from one medium to another of a different density. The change in wave speed causes the light to bend, a principle used in the design of lenses and optical instruments.
| Feature | Reflection | Absorption | Transmission |
|---|---|---|---|
| Direction | Bounces back into the first medium | Stays within the second medium | Passes into the second medium |
| Energy Change | Energy remains as wave energy | Energy converts to heat/internal | Energy remains as wave energy |
| Surface Role | Primary site of interaction | Secondary to bulk properties | Primary entry point to bulk |
| Visual Effect | Creates highlights or images | Determines darkness/pigment | Creates transparency/clarity |
Check the Normal: Always ensure that angles of incidence and reflection are measured from the normal line (90 degrees to the surface), not from the surface itself. This is the most common source of calculation errors in optics problems.
Energy Summation: In problems involving percentages, verify that the percentages of reflection, absorption, and transmission add up to exactly 100%. If a problem states an object is opaque, you must assume transmission is zero.
Color Logic: Remember that the color you see is the light that was not absorbed. If an object absorbs all colors except blue, it will appear blue; if it absorbs all colors, it appears black.
Surface Texture: Distinguish between the law of reflection (which always holds) and the type of reflection (specular vs. diffuse). Even in diffuse reflection, the angle of incidence equals the angle of reflection for every individual photon.
