The focal length, f, is the defining parameter of most lenses and mirrors. See also focal length incident Falling or shining upon. When light is incident on something, the light may be reflected , refracted , absorbed, or any combination of these. A number signifying how well a material can refract light. Usually specified as n by scientists, the index of refraction of a material depends on its composition and density.
Mirrors can also magnify objects.
Or, more specifically, investigation by means of a microscope. If one line is normal to another, then they are at right angles to each other. A phenomenon discovered by Einstein in the early 20th century in which electrons are ejected from a solid when impinged upon by electromagnetic radiation. This led to the understanding of light as particles, or photons . The energy required to strip an electron from an atom is called the ionization energy.