Law of Reflection

The law of reflection states that the angle of incidence equals the angle of reflection.
Illustrated in Figure 28.5, this principle applies to all angles of incidence.
Practical application: White coatings on roofs can reflect up to 85% of incident light, helping to reduce air conditioning costs and carbon emissions during hot summer days.
For effective energy saving, it is recommended to paint rooftops white, especially in regions with hot summers.
There are also double-layered paints available that reflect infrared light while maintaining color.

Angles of incidence and reflection are measured from an imaginary line called the normal, which is perpendicular to the reflecting surface.
The incident ray, the normal, and the reflected ray are all co-planar, or in the same plane.

Specular Reflection:
- Occurs on smooth surfaces, like mirrors.
- Mirrors provide excellent specular reflections, as per Figure 28.6.

When light rays from an object (e.g., a candle) hit a mirror, they reflect at the same angles as their angles of incidence.
The reflected rays appear to come from a virtual image behind the mirror. For example:
- If a candle flame radiates light, the light reflects off the mirror, forming an image at a point where the dashed lines (representing extended reflected rays) converge.
Virtual Image:
- The virtual image is located behind the mirror, equal in size to the object, but it does not actually emanate from that point.
- The distance from the mirror to the virtual image equals the distance from the mirror to the object.
This phenomenon implies that in a flat mirror, the left-right orientation reverses, while the up-down orientation remains unchanged.

Unlike flat mirrors, curved mirrors (concave and convex) cause variations in sizes and distances for images.
- Concave mirrors can produce larger virtual images that appear further away from the mirror.
- Convex mirrors provide smaller virtual images closer to the mirror.
In curved mirrors, unlike flat mirrors, normals are not parallel, affecting the reflection angles at various points on the mirror.

Only about 4% of light is reflected from typical surfaces like clear glass at normal incidence, while polished surfaces (e.g., silver) can reflect about 90%.
Diffuse reflection occurs on rough surfaces where light is scattered in many directions, allowing visibility from multiple angles.

Diffuse Reflection:
- Occurs when light reflects off rough surfaces, scattering in many directions and producing no mirror images.
- An example is the walls of a room or the surface of paper, which reflects light in a diffused manner.
The roughness of a surface is related to the wavelength of light, affecting the reflection type—smooth surfaces for longer wavelengths may appear polished while being rough for shorter wavelengths.
Wet surfaces reflect less light due to multiple reflections and increased absorption, resulting in a darker appearance than dry surfaces.