Refraction of Light at Curved Surfaces

Ray passing along the principal axis, Ray passing through the optic center

Only rays passing along the principal axis and through the optic center pass undeviated. Parallel rays converge at focus, and rays through focus become parallel.

m = v/u

Magnification m = v/u = height of image/height of object. Here v is image distance and u is object distance from the lens.

Always negative

For a concave (diverging) lens, the focal length is always negative according to the sign convention, as the focus is on the same side as the object.

Virtual, Erect, Magnified

When object is between focal point and optical center of convex lens, image is virtual (cannot be captured on screen), erect (upright), and magnified (larger than object).