One surface of a lens is convex and the other is concave. If the radii of curvatures are R and r respectively, the lens will be convex if

Step-by-step solution

The lens maker formula is given by 1 f = ( - 1) ( 1 R₁ - 1 R₂ ) . For a lens with one convex surface and one concave surface, let the radius of the convex surface be R₁ = R and the radius of the concave surface be R₂ = r . By sign convention, for a convex surface facing the object, R₁ is positive, and for a concave surface, R₂ is also positive if the center of curvature lies on the same side as the light direction. The focal length f is given by 1 f = ( - 1) ( 1 R - 1 r ) . For the lens to be convex (converging), t