A convex lens is a polished piece of glass that is curved outward on both sides of the lens. A magnifying glass is an example of a simple convex lens. The cornea in a person's eye is another example of a convex lens. These lenses are used in everyday life.
A Magnified Image
A convex lens magnifies an image for the person looking through the lens at a stationary object. The light rays which enter the lens are bent toward each other, pass through a central focal point and then diverge again. The divergent light rays create the image of the object, which is larger than the image itself.
Lens Focal Length
A convex lens has a specific focal length. The focal length is the distance from a center line running through the lens to the point at which the light rays converge into a single point. Imagine four people walking along a residential driveway on parallel paths. As they cross a crack in the driveway, they alter their path so they are all walking at an angle, towards a pop bottle that is placed at the end of the driveway ahead of them. As they reach the pop bottle, they all collide, as they attempt to occupy the same place at the same time. The distance from the pop bottle to the driveway crack is the distance called the lens focal length. The larger a lens focal length, the more an image will be magnified by the lens.
Concentrating Light Rays
Because convex lenses bend light rays toward a single focal point, convex lenses can be used to concentrate energy. A child's magnifying glass can concentrate sun rays into a single point that is hot enough to start a piece of paper on fire or burn a hole through clothing or tennis shoes. The light rays from the sun enter the convex lens traveling parallel to one another. As the light rays leave the lens, they are bent and focused towards a single point.
Convex lenses also invert an image which passes through the lenses. Convex lenses are used in cameras. When a camera is focused on a distant object, the image of that object appears inverted on the camera film. The light rays perform the same way in the back of a human eyeball. The cornea, a convex lens, focuses on an object and then creates an inverted image on the back of the person's eyeball, where the image is collected by the brain's optic nerves. The brain corrects the upside-down image and recognizes that the objects are actually right side up.
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