An observer's perception of an object being examined changes with a magnifying lens because the lens bends the light rays from the object, thus distorting the size of the image formed, making it appear bigger. Light rays bend due to a change in density as they move from air to the glass that forms the lens. If light rays did not bend, no magnification would occur.
Lenses work based on the concept of refraction. Refraction occurs only when light moves from one medium to another, provided the two media have different densities. Light travels at different speeds in different media. When the speed of light changes, the light ray bends. When light from an object hits the magnifying lens, it begins to move in glass instead of air. Light travels slower in glass. This change in velocity causes the light to bend. The bending of light results in a distortion in the image formed. The amount of distortion in the image depends on the distance of the lens from the object. Every lens has a focal point, which is the distance at which the lens can focus the light shining on it to a single point. If the object is placed between the focal point of the lens and the lens itself, the image will look bigger than the actual object.