Reflection of light
- Reflection of light can be either specular (mirror-like) or diffuse (retaining energy but losing the image).
- Specular reflection occurs at the surface of a mirror or transparent media like water or glass.
- The angle of incidence equals the angle of reflection, according to the law of reflection.
- Reflection can occur when light travels from a medium with one refractive index to a medium with a different refractive index.
- Total internal reflection occurs when the angle of incidence is greater than the critical angle, and it is used in applications like X-ray telescopes.
Laws of reflection
- Specular reflection occurs when the reflecting surface is very smooth.
- The incident ray, reflected ray, and normal to the reflection surface lie in the same plane.
- The angle of incidence is equal to the angle of reflection.
- The reflected ray and the incident ray are on opposite sides of the normal.
- These laws can be derived from the Fresnel equations.
- Diffuse reflection occurs when light strikes the surface of a non-metallic material and bounces off in all directions.
- It is caused by multiple reflections by microscopic irregularities inside the material and on its surface.
- The exact form of diffuse reflection depends on the structure of the material.
- Lambertian reflectance is a common model for diffuse reflection, where light is reflected with equal luminance or radiance in all directions.
- Diffuse reflection is the primary mechanism of physical observation for most objects we see.
- Retroreflection is a phenomenon where light is returned in the direction from which it came.
- Some surfaces exhibit retroreflection, such as those with curved droplets or corner reflectors.
- Retroreflection can be seen when flying over clouds or with dew on grass.
- Animals like cats and dogs have retinas that act as retroreflectors, improving their night vision.
- Retroreflective surfaces can be created using mirrors or by depositing refractive spheres or pyramid-like structures.
- In classical electrodynamics, light is considered as an electromagnetic wave described by Maxwell's equations.
- Light waves induce small oscillations of polarization in atoms or electrons, causing each particle to radiate a small secondary wave.
- The combination of these secondary waves gives rise to specular reflection and refraction.
- In dielectrics like glass, the electric field of light acts on electrons, generating forward and backward radiation that contributes to refraction and reflection.
- In metals, free electrons oscillate with incident light, resulting in cancellation of forward radiation and reflection of backward radiation.
Multiple reflections (subtopic)
- Light reflects off a mirror, creating one image.
- Two mirrors placed face to face produce an infinite number of images along a straight line.
- Multiple images between two mirrors at an angle lie over a circle.
- Four mirrors placed face to face create an infinite number of images in a plane.
- Multiple images between four mirrors forming a pyramid lie over a sphere.
Complex conjugate reflection
- Phase conjugation causes light to bounce back in the opposite direction.
- Wavefronts are reversed in complex conjugate reflection.
- Conjugate reflectors can remove aberrations from a beam.
- Looking into a complex conjugating mirror would appear black.
- Only photons that left the pupil would reach the pupil in a complex conjugating mirror.
Other types of reflection
- Neutron reflection
- Beryllium and other materials reflect neutrons.
- Neutron reflection is used in nuclear reactors and weapons.
- Reflection of neutrons off atoms helps determine internal structure in science.
- Sound reflection
- Longitudinal sound waves reflect in a coherent manner on a flat surface.
- Reflection of sound depends on the texture and structure of the surface.
- Porous materials absorb some sound energy.
- Rough surfaces scatter sound energy in many directions.
- Sound reflection affects the acoustic space and is important in architectural acoustics.
- Seismic reflection
- Seismic waves produced by earthquakes are reflected by layers within the Earth.
- Reflection seismology uses shallow reflections to study the Earth's crust and prospect for petroleum and gas deposits.
- Deep reflections of earthquake waves help determine the layered structure of the Earth.
- Seismic reflection has contributed to understanding the Earth's composition.
- Reflection seismology is used in oil and gas exploration.
Reflection (physics) Data Sources