Answer:
When light passes through a medium with a different refractive index, it bends due to the change in speed of the light. This phenomenon is called refraction. When light passes through a lens, which is a transparent object made of a material with a different refractive index than air, the lens refracts the light in a specific way depending on its shape.
A concave lens is thinner at the center and thicker at the edges. When light passes through a concave lens, it is refracted in such a way that the light rays are spread out, or diverge. This is because the lens surface curves outward, causing the light rays to bend away from the center of the lens. The point where the light rays appear to originate from is called the virtual focus, and it is located on the same side of the lens as the object. Concave lenses are commonly used in eyeglasses to correct nearsightedness, as they spread out the light coming from a nearby object and allow it to be properly focused on the retina.
A convex lens, on the other hand, is thicker at the center and thinner at the edges. When light passes through a convex lens, it is refracted in such a way that the light rays are converged, or focused, to a point called the focal point. This is because the lens surface curves inward, causing the light rays to bend towards the center of the lens. The distance between the lens and the focal point is called the focal length. Convex lenses are commonly used in eyeglasses to correct farsightedness, as they help converge the light from distant objects and allow it to be properly focused on the retina.