• Reflection is the change in direction of a wavefront at an interface between two different media so that the wavefront returns into the medium from which it originated.


  • the change in direction of a wave passing from one medium to another caused by its change in speed.

Index of Refraction

  • Light travels slower in different media than vacuum.
  • A higher n means a slower velocity
  • The index of refraction can depend on the wavelength of the light.

Refractive Index

  • The refractive index or index of refraction of a material is a dimensionless number that describes how fast light travels through the material. It is defined as where c is the speed of light in vacuum and v is the phase velocity of light in the medium.

Snell’s Law

  • Snell’s law is a formula used to describe the relationship between the angles of incidence and refraction, when referring to light or other waves passing through a boundary between two different isotropic media, such as water, glass, or air.

Total Internal Reflection

  • Total Internal Reflection is the phenomenon that makes the water-to-air surface in a fish-tank look like a perfectly silvered mirror when viewed from below the water level.


  • Dispersion’ is the property by which light is spread out according to its color as it passes through an object.
  • The separation of light is dispersion


  • A mirror is an object that reflects light in such a way that, for incident light in some range of wavelengths, the reflected light preserves many or most of the detailed physical characteristics of the original light, called specular reflection. This is different from other light-reflecting objects that do not preserve much of the original wave signal other than color and diffuse reflected light, such as flat-white paint.


  • A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses, usually arranged along a common axis.


  • A focus, also called an image point, is the point where light rays originating from a point on the object converge. Although the focus is conceptually a point, physically the focus has a spatial extent, called the blur circle.

Focal Point

  • The point at which rays or waves meet after reflection or refraction, or the point from which diverging rays or waves appear to proceed.

Convex Mirror

  • Rays towards the focal point leave parallel
  • Rays parallel reflect directly away from the focal point.
  • The image is at the crossing of the extended rays       

Concave Mirrors

  • A concave mirror, or converging mirror, has a reflecting surface that is recessed inward (away from the incident light). Concave mirrors reflect light inward to one focal point. They are used to focus light.

Optical Instrument

  • Optical instruments are the devices which process light wave to enhance an image for more clear view. Use of an optical instruments, such as a magnifying lens or any complicated device like microscope or telescope usually makes things bigger and helps us to see in a more detailed manner.

Lens Aberration

  • Lens aberration occurs from imperfections in the optics model
  • Monochromatic aberrations are caused by the imperfection of the geometric ray model.
  • Chromatic aberrations occur because of the differences in wavelengths of light
  • Aberrations can be reduced with extra optics

Lens Maker’s Formula

  • The lens maker’s equation is another formula used for lenses that give us a relationship between the focal length, refractive index, and radii of curvature of the two spheres used in lenses.


  • A microscope is an instrument used to see objects that are too small to be seen by the naked eye.
  • Basic microscopes place an object inside the focal length, creating a large virtual image.


  • A telescope is an optical instrument that makes distant objects appear magnified by using an arrangement of lenses or curved mirrors and lenses, or various devices used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation.
  • Basic telescopes use two lenses to increase the size of an object

Visual Angle

  • The visual angle is the angle a viewed object subtends at the eye, usually stated in degrees of arc. It also is called the object’s angular size. The diagram on the right shows an observer’s eye looking at a frontal extent that has a linear size, located in the distance from point.
  • The visual angle is greater. It is also called the angular size.

Angular Magnification

  • The ratio of the angle subtended at the eye by the image formed by an optical instrument to that subtended at the eye by the object when not viewed through the instrument.

The Human Eye

  • The human eye is an organ that reacts to light and allows vision. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth.