Ronit uses a lens of focal length +40 cm and his brother Shobhit uses a lens of focal length -40 cm. What is the nature of the lens and its power used by each of them?

Solution,
A positive focal length of a lens means the lens is converging in nature while a negative focal length means the lens is diverging in nature.
So, Ronit's lens is converging in nature and must be a convex lens while Shobhit's lens must be diverging in nature and must be a concave lens.
Power of a lens is defined as:
Power (P)=1Focal length (F) (in m) (Diopters)The power of the lens of Ronit is:P=10.40 m=+2.5 DandThe power of the lens of Shobhit is:P=1-0.40 m=-2.5 D

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