A magnifying glass is an example of a convex lens.
When a ray of light passes from one transparent medium to another, it may change direction as it does so, depending on its speed in each medium and its angle to the surface. This phenomenon is called refraction and explains how lenses work.
Types
Broadly speaking, two basic types of lenses exist: convex lenses, which bulge outward or are thicker at the center, and concave lenses, which bulge inward or are thinner at the center. Convex lenses focus light,while concave lenses scatter it, so while a convex lens can magnify objects, a concave lens cannot.
Effects
A lens works by refracting rays of light as they pass through the lens. Refraction takes place because light travels more slowly through glass than it does through air, so the wave is bent slightly off course in the glass. If the two glass surfaces are parallel, then the light ray that emerges will be traveling parallel to the original ray. Consequently, in both convex and concave lenses, light rays that pass through one end of the lens are bent while light rays that pass through the center are undeflected.
Function
The index of refraction of a substance is equal to the speed of light in a vacuum---a fundamental constant of the universe---divided by the speed of light in the substance. Diamond, for example, has an index of refraction of 2.419, while ice has an index of refraction of 1.3. The angle of a ray of light passing through an interface between two media is given by Snell's Law, n1 sin (angle 1) = n2 sin (angle 2), where angle 1 is the angle off the perpendicular at which the light ray strikes the surface between the two media and angle 2 is the angle off the perpendicular at which the ray travels inside the second medium. Light traveling through a lens is refracted twice, once as it enters and once as it emerges.
Tags: angle angle, concave lenses, index refraction, pass through, through lens