Prisms
Prisms are transparent objects that manipulate light through a process known as refraction, which alters the direction, speed, or wavelength of light as it passes from one medium to another. Commonly, prisms are triangular and made of glass or plastic, and they are best known for their ability to disperse visible light into a spectrum of colors, creating a rainbow effect. This phenomenon was notably studied by Sir Isaac Newton in the seventeenth century, who demonstrated how different wavelengths of light are refracted at varying angles. While many prisms are designed to separate light based on wavelength, others are used to redirect light without dispersion, such as in binoculars or telescopes. Prisms also play a role in the polarization of light waves, which is the alignment of light in a particular plane; for instance, Nicol prisms utilize double refraction to achieve this. Everyday applications of prisms range from optical devices like cameras and projectors to safety items like polarized sunglasses that reduce glare. Overall, prisms are essential tools in the field of optics, enhancing our ability to observe and understand the properties of light.
Prisms
FIELDS OF STUDY: Optics; Electromagnetism
ABSTRACT: Prisms are transparent objects that refract (bend) light that passes through them. Some prisms also reflect light, while others—particularly the common triangular prisms—disperse visible light into its component wavelengths, producing a rainbow-like effect. Prisms work under the principles of electromagnetism. When passing from one medium to another, the speed and direction of travel of electromagnetic waves are changed.
PRINCIPAL TERMS
- dispersion: the process by which light is split into its spectrum of wavelengths as it passes through a medium.
- electromagnetic spectrum: the range of wavelengths that make up electromagnetic radiation. These include visible light, infrared, and ultraviolet light.
- optics: the branch of physics devoted to the study of light and vision.
- polarization: the process by which the motion of electromagnetic waves, which is perpendicular to the direction of energy transfer, is brought into alignment in the same plane.
- refraction: the change in a wave’s path, speed, or wavelength when the wave passes between two media.
- visible light: a form of electromagnetic radiation that represents the limited range of the electromagnetic spectrum that the human eye can see.
- wavelength: the full length of a complete wave cycle, measured as the distance between adjacent crests or troughs of a wave.
How Prisms Work
Light undergoes refraction, or a change in its direction, speed, or wavelength, as it passes through a prism, which is a transparent object. In common parlance, "prism" often refers specifically to a small, triangular object made of glass or plastic that refracts visible light in such a way that it splits into a rainbow-like series of colors. Sir Isaac Newton (1642–1727) was one of the first to understand this phenomenon through the use of a prism in the seventeenth century. In optics, a prism may be made of any transparent material, come in a variety of shapes, and have a variety of effects including reflection or magnification.
The angle of refraction, or bending, of light varies by wavelength in many media. Short-wavelength visible light, such as blue light, may be refracted at a greater angle than long-wavelength visible light, such as red. As a result, light passing through a prism ends up sorted by wavelength. This produces a rainbow-like effect wherein the colors that comprise visible light are separated by their differing wavelengths. This process is referred to as dispersion.
Visible Light and the Electromagnetic Spectrum
What humans see as visible light is in fact a form of electromagnetic (EM) radiation. EM radiation is energy that travels as waves. Examples include infrared radiation, ultraviolet radiation, and radio waves. The electromagnetic (EM) spectrum sorts all forms of EM radiation into categories by its wavelength. Within visible light, the distinct colors recognizable to the human eye each occupy their own subrange of wavelengths.
Not all prisms are dispersive. Some are used to redirect light without dispersion, bouncing light that enters in a desired direction—this is often the case with prisms used in binoculars to ensure the image reaches the user’s eye right-side-up. Prisms can also split beams of light into multiple beams.
Prisms and Polarization
EM waves are a type of transverse wave: the wave moves perpendicular to the direction of energy transfer. For example, ocean waves move up and down while transferring energy horizontally across the surface of the ocean. EM waves are a bit different in that they do not typically move in the uniform manner of ocean waves. Instead, EM waves may take any number of orientations.
Prisms can be used in the polarization of light waves. The Nicol prism, for example, uses double refraction to split a beam of light into two paths. This allows one of the light waves, which has become polarized, to be restricted and filtered to a single plane. Similarly, polarized sunglasses filter out partially polarized light to eliminate glare.
Prisms in Everyday Life
Prisms can be found in a variety of everyday devices, from the laser in a computer’s CD drive, to the interior of a pair of binoculars, to a backyard telescope. Prisms are used in conjunction with lenses to capture, focus, and redirect light. This makes it possible to see things that an unaided human eye would be incapable of detecting.
Bibliography
"Anatomy of an Electromagnetic Wave." Mission: Science. NASA, n.d. Web. 13 July 2015.
Bass, Michael, ed. Handbook of Optics. 3rd ed. 5 vols. New York: McGraw, 2010. Print.
"Electromagnetic Radiation." Encyclopaedia Britannica. Encyclopaedia Britannica, 26 Nov. 2014. Web. 13 July 2015.
"Introduction to Optical Prisms." Edmund Optics Worldwide. Edmund Optics, n.d. Web. 13 July 2015.
Morgan, Erinn. "Polarized Sunglasses." All about Vision. Access Media Group, May 2014. Web. 14 July 2015.
Parry-Hill, Matthew, and Michael W. Davidson. "Birefringent Polarizing Prisms." Microscopy Resource Center. Olympus America, n.d. Web. 13 July 2015.
Yacoubian, Araz. Optics Essentials: An Interdisciplinary Guide. CRC, 2015. Print.