The focal length of a lens is the distance between the principal focus and the optical center of the lens. It is represented by the letter f. For a concave lens, the focal length is considered negative, indicating that the principal focus is on the same side as the incident parallel rays.
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The focal length of a lens is the distance between its optical center (the point where the optical axis intersects the lens) and its principal focus. It is the point where parallel rays either converge (for converging lenses) or appear to diverge from (for diverging lenses). The focal length is represented by the symbol “f” and is measured in meters. For converging lenses, the focal length is positive, while for diverging lenses, it is negative. The magnitude of the focal length indicates the lens’s ability to converge or diverge light, influencing optical applications like magnification and image formation.