The focal point is the specific point where light rays parallel to the principal axis converge after passing through a lens or reflecting off a mirror. It is crucial for understanding image formation in optical systems.
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The distance from the lens to the focal point is called the focal length.
A convex lens has a positive focal length and converges light rays, forming a real image at its focal point.
A concave lens has a negative focal length and diverges light rays, such that they appear to originate from its focal point, forming a virtual image.
For mirrors, the type of mirror (concave or convex) determines whether the focal point is real or virtual.
In geometric optics, the focal point is essential for determining image location, size, orientation, and type using ray diagrams.