What is a Prism: Definition, Characteristics, Core Elements and Real-Life Applications

Have you ever wondered why we see a rainbow? This optical illusion is caused due to refraction, reflection and dispersion of sunlight when it passes through the tiny water droplets in the sky. The tiny raindrops act as a prism to scatter light in seven colours. You can also make your own rainbow by using a prism. In this article, we will learn what prism is, how it works along with its real-life applications.

Table of Contents

• What is a Prism
• Elements of a Prism
• Uses of Prism

What is a Prism

A prism is a 3-dimensional object with parallel identical ends and has a parallel surface. The word prism is derived from the Greek word prisma which means something sawn. This name is due to the straight cut edges of prisms that look like sawed from a larger shape. Most prisms are made of glass or other materials such as plastic, germanium or zinc.

Elements of a Prism 

A prism has many well-defined structural elements. Understanding these components is essential for understanding its optical behaviour, as well as for practical applications in engineering and manufacturing.

Bases: The bases are the two congruent, parallel polygonal faces at opposite ends of the prism that give the prism its name. For example, a triangular prism has triangular bases and a rectangular prism has rectangular bases. They lie in parallel planes and are always identical in shape, size and orientation. 

Lateral Faces: The faces that connect corresponding edges of the two bases. Every lateral face shares one edge with each of the two bases. The number of lateral faces always equals the number of sides of the base polygon. In a right prism, all lateral faces are rectangles; in an oblique prism, they are parallelograms.

Edges: A prism has three sets of edges, including those of the top base, of the bottom and the lateral edges connecting corresponding vertices of the two bases.

Vertices: The corner points of the prism where edges meet are called vertices. The vertices of a prism are twice the number of sides of its base polygon.

Uses of Prism

Prism is one of the most widely used devices with many applications in different disciplines including physics, astronomy, photography, architecture, engineering, education, art and medicine. Here are some of the major applications of prisms:

Dispersion of Light: Prism is used for dispersion of white light into the visible spectrum. When a beam of white light enters a glass prism, each wavelength is refracted by a different amount. This technique is used for scientific analysis of light coming from stars or chemical flames that help us understand the composition of samples. 

Astronomy and Astrophysics: By dispersing light from stars and galaxies spectrographs attached at top of telescopes reveal absorption lines that identify the elements that are present. 

Optical Instruments: Prisms are used in optical instruments such as binoculars and telescopes to redirect and correct light paths. In binoculars, porro prisms or roof prisms fold the light path, allowing the instrument to be compact while still providing sufficient magnification. 

Photography: Prisms are used in photographic digital SLR cameras. Inside the viewpoint system of the camera there is a pentaprism or penta-mirror. The camera lens captures an inverted, laterally reversed onto a focusing screen which then it corrects.

Fiber Optics: Coupling prisms are used to inject laser light into thin-film waveguides and optical fibres, enabling fibre optic communications and medical endoscopy systems.

Laser Technology: Prisms perform critical beam-shaping and directing functions. They are used inside laser cavities to select polarisation and reduce reflection losses. Prism beam expanders are used to reshape elliptical laser beams into circular profiles.

Ophthalmology: Prism is used in ophthalmology to measure and fix eye alignment.