power 4dPower of the lens (P) = 4 D. Refractive Index (r) = 1.5. To Find: The radius of curvature. Calculations: The following equation determines a lens's power: where P is the power ofAnswer:the power of a convex lens is always positive. as you can see here the power is +4D, therefore the nature of the lens is that it is a convex lens. we know, P = 1f. also