# Shared Flashcard Set

## Details

Light Concepts and Design
Optics and Light - Study Guide
40
Physics
12/01/2012

Term
 How does light influence how we perceive an object or person?
Definition
 The way light illuminates an object helps define how think or feel about that object.   By changing the color, angle, intensity and focus of the light we can make the audience feel a certain way about what is going on.
Term
 What are the properties of a particle?
Definition
 Photons and Electrons   Measurable: Mass, Charge, Spin and Decay
Term
 Why can light be considered a particle?
Definition
 Due to the Photoelectric Effect (E = hf):   Increasing the intensity of light and it increases the number of electrons emitted from the surface but doesn’t increase the energy of each electron.
Term
 What are the properties of a wave?
Definition
 A wave is a transfer of energy from one point to another without the transfer of a material between the two points. The main properties of waves are defined below. •Amplitude: the height of the wave, measured in meters. •Wavelength: the distance between adjacent crests, measured in meters. •Period: the time it takes for one complete wave to pass a given point, measured in seconds. •Frequency: the number of complete waves that pass a point in one second, measured in inverse seconds, or Hertz (Hz). •Speed: the horizontal speed of a point on a wave as it propagates, measured in meters / second.
Term
 What does diffraction mean?
Definition
 The bending of waves around obstacles, or the spreading of waves by passing them through an aperture, or opening.
Term
 What does reflection mean?
Definition
 The phenomenon of a propagating wave (light or sound) being thrown back from a surface.
Term
 What does refraction mean?
Definition
 The bending of light rays or waves as they go from one material to another due to the differences in velocities in the material.
Term
 Why can light be considered a wave?
Definition
 Light is made up of packets, or chunks, of light in which Einstein called them photons. The photons have energy and vibrate. Light travels as particles and waves and both have been proven. The double slit experiment showed that light traveled as a wave but the “photoelectric effect,” as well as the “Davisson-Germer” experiment showed light as a particle.
Term
 What is wave-particle duality?
Definition
 Principle of quantum mechanics implying that light (and, indeed, all other subatomic particles) sometimes acts like a wave, and sometime acts like a particle, depending on the experiment being performed. For instance, low frequency electromagnetic radiation tends to act more like a wave than a particle; high frequency electromagnetic radiation tends to act more like a particle than a wave.
Term
 What is the visible spectrum?
Definition
 The Visible Spectrum is that part of the Electromagnetic Spectrum which can be seen with the naked eye. It consists of the frequencies between 380 nanometers and 780 nanometers (400-700nm). It consists of the colors Violet, indigo, blue, green, yellow, orange and red.
Term
 How is light created?
Definition
 There are two basic types of light: -Incandescence                                        -Luminescence    Vibration of an atom                                  Vibration of electrons      Thermal or blackbody emission                 Lower temperature      Heating it up until there is light                 Change of energy level releases photon
Term
 What is the smallest particle of light, as we know it today?
Definition
 Photons
Term
 What does a reflector do?
Definition
 It re-directs light from the source to give it a specific shape and focus.
Term
 What is the Law of Specular Reflection?
Definition
 The angle of incidence equals the angle of reflection.
Term
 What is the point of incidence?
Definition
 The point of incidence is the point where the ray of incidence strikes the mirror.
Term
 What is the normal line?
Definition
 The normal line is a line drawn perpendicular to the surface at the point of incidence.
Term
 What is the angle of incidence?
Definition
 The angle between the incident (incoming) light ray and the normal line.
Term
 What is the angle of reflection?
Definition
 The angle between the reflected (outgoing) light ray and the normal line.
Term
 What are three types of reflectors?
Definition
 •Ellipsoidal Reflector – A concave ellipsoidal surface used to focus rays from a light source at the near focal point onto the opposite focal point of the ellipse.•Parabolic Reflector – A reflective surface generated by rotating a parabolic section around its axis. A light source placed at the focal point of the reflector will create a reflected beam of concentrated collimated light parallel to the axis of the reflector.•Spherical Reflector – A reflector shaped like a portion of a sphere so that light from a point source at the center point of the sphere will be reflected back through the center point of the sphere.
Term
 What does a specular reflector do?
Definition
 A reflecting surface (polished metal or silvered glass) that gives a direct image of the source, with the angle of reflection equal to the angle of incidence (The Law of Specular Reflection). Also known as regular reflector.
Term
 What does a diffuse reflector do?
Definition
 -A diffuse reflector will spread light in all directions.-There are certain types of diffuse reflectors that offer more control. •They are known as Spread Reflectors. A spread reflector will scatter the light but all reflected rays will be travelling along the same plane. •Diffuse Reflectors will scatter light in such a way that each individual light ray in the beam strikes a point that will be different from the neighboring point.
Term
 What do lenses do?
Definition
 They will bend light through the process of refraction.
Term
 What does a spread reflector do?
Definition
 A spread reflector will scatter the light but all reflected rays will be traveling along the same plane.
Term
 What is a near zero reflector?
Definition
 Has almost no reflection.
Term
 What is a near perfect reflector?
Definition
 The surface of a perfect mirror reflects the incident ray without any attenuation. However, there is no such thing as a surface that will yield a perfect specular reflection due to the fact that it is impossible to polish a surface to a level where there are no facets at an atomic level. Even on the flattest of flat surfaces, there will be facets to some extent.
Term
 What does an ellipsoidal reflector do to the light?
Definition
 By mathematical definition an Ellipsoid has two focal points. When a reflector is placed at the focal point at that end, all rays of the light that strike the reflector will be diverted through the second focal point. The result is that an enormous percentage of the light from the source is directed in a manner that makes it easily usable. Ellipsoidal reflectors can improve the efficiency of an instrument by 75%.
Term
 What does a spherical reflector do to the light?
Definition
 If a light source is placed in the center of a spherical reflector, all of the rays will be reflected back 180 degrees of their original trajectory. This gives almost double the light output than would occur without the reflector. A spherical reflector will increase the efficiency of a lighting instrument by 40%.
Term
 What does a parabolic reflector do to the light?
Definition
 If a light source is placed in the focal point of a parabolic reflector, the rays of light will be reflected parallel to one another. This will give a great concentration of light in a tight beam, rather than an effused spread. Moving the source toward the reflector will spread the light, while moving the source away from the reflector will cause the light rays to converge.
Term
 What does an asymmetrical reflector do to the light?
Definition
 This reflector is not symmetrical around its axis as the previous reflectors have all been. In addition, the lamp is offset instead of being placed in the center of the reflector.
Term
 What is a medium?
Definition
 A wave is a moving vibration through some material. That material is called the medium. Well-known examples are the surface waves of water (water is the medium) and sound (air is the medium).
Term
 What is optical density?
Definition
 Optical density controls the index of refraction. If the light is moving from a medium with a low optical density (smaller index of refraction) to one of high optical density (bigger index of refraction) the light will bend towards the normal line.
Term
 What is the speed of light in a vacuum?
Definition
 186,200 miles per second.
Term
 What is the Index of Refraction?
Definition
 The ratio between the speed of light in a vacuum and the speed of light in a medium is known as the index of refraction (speed of light in a vacuum divided by speed of light in the medium) and tells us how much the light will bend when it crosses the boundary between mediums.
Term
 How does light bend when crossing from a medium of a low optical density to a medium of a high optical density?
Definition
 The light will bend towards the normal line.
Term
 How does light bend when crossing from a medium of high optical density to a medium of low optical density?
Definition
 The light will bend away from the normal line.
Term
 When light is passing through a medium with non-parallel surfaces, how does the light bend?
Definition
 When the two surfaces are not parallel the bending is compounded due to the changing angle of the incident light at the normal line and the emergent ray will not be parallel to the incident ray.
Term
 What is the focus point of a lens?
Definition
 Where the parallel rays of the light converge.
Term
 What is the optical center of a lens?
Definition
 The optical center is an imaginary plane, based on the radii of the curvature of the surfaces of the lens, where light appears to bend in the lens. The Optical Center (vertical) may be the physical center of the lens if the curvatures of the opposite sides are the same or it may be offset if the curvatures are different.
Term
 What is the optical axis?
Definition
 The optical axis is a line drawn (horizontal) through the physical center of the lens.
Term
 What is the focal length of a lens?
Definition
 The focal length is measured along the optical axis from the optical center of the lens to the focal point.
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