Please help with theses 2 questions. 1. What is the name of 2F?

2.Using the diagram what is the name of the distance between O and 2F?

1) Well, we know that lens is made by using 2 concave or convex mirror or sometimes we also use one plane mirror. The spherical mirrors are part of the glass sphere, and hence they have a centre and corresponding radius.

2F is double of focal length when light passes from one surface to another of the lens, so it can be said as the centre of curvature of the one of those spherical lens.

2) Distance between the optical centre and the centre of curvature is a lens can be termed as the radius of curvature of the lens. Well, we don't generally use these in case of lens. But still, the distance between O and 2F is double of the focal length or radius of curvature.

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