A double-convex lens of power 4 D is manufactured from a glass

power 4dAnswer: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. alsoThe power of a lens is +4D. Find the focal length of this lens. An object is placed at a distance of 50 cm from the optical centre of this lens. State the nature