Convex lenses are thicker in the middle and thinner at the edges, causing light rays to converge towards a focal point. Concave lenses are thinner in the middle and thicker at the edges, causing light rays to diverge.
Lenses refract light by changing the direction of light rays as they pass through the lens. The amount of refraction is determined by the shape of the lens and the difference in refractive index between the lens and the surrounding medium.
The focal length of a lens is the distance between the lens and its focal point, where parallel light rays converge or diverge after passing through the lens. It is measured in meters (m) or centimeters (cm).
The shape of a lens determines how light rays will be refracted as they pass through. A thicker lens will cause more refraction, while a thinner lens will cause less. The shape also determines the focal length and the type of image formed (real or virtual) by the lens.
A converging lens (convex) causes light rays to converge towards a focal point, while a diverging lens (concave) causes light rays to diverge. Converging lenses are used to form real images, while diverging lenses are used to form virtual images.