Light, Prism and Lens

Study of light is optics. Geometrical optics/Ray optics deals with phenomena without taking account their nature. In a converging beam, the rays of light move towards a point. In a diverging beam, the rays of light spread out from a point. In a parallel beam, the rays of light are parallel to one another. The material medium or space through which light propagates is called an optical medium. Prism is an optical medium bounded by three rectangular faces and two triangular faces which are parallel to each other. Any section of the prism perpendicular to the refracting edge is called the principal section of the prism. Spherical surface is a portion of a solid sphere. The area of the spherical surface available for refraction is called aperture. The midpoint of the spherical surface is called pole. A lens is an optical medium bounded by two surfaces of which at least one is spherical/cylindrical. Commonly used lenses have either 2 spherical surfaces or one spherical and one plane surface. These lenses are called spherical lenses. Convex lens assumes thick shape at middle than edges while concave lenses assume thick edges. A lens that converges light is called converging lens and a lens which diverges parallel beam is called a diverging lens. Principal axis of a lens is a straight line passing through the centers of curvature of two spherical surfaces of the lens. The power of the lens is the ability of the lens to converge or to diverge a beam of light and it is measured by the reciprocal of its focal length. Linear magnification produced by a lens in a direction perpendicular to the principal axis is defined as the ratio of the linear size of the image to the linear size of the object.