Q33 of 84 Page 322

Two lenses have power of (a) + 2D (b) – 4D. What is the nature and focal length of each lens?

Power P1 = 2D;

Since Power is positive. Therefore, the lens is convex lens.



⇒


⇒


1m = 100cm


⇒ 0.5m = 50cm.


Hence the focal length is 50cm


P2 = -4D.


Since the power is negative. Therefore, the lens is concave lens.



⇒


⇒


1m = 100cm


⇒ 0.25m = 25cm.


Hence the focal length is -25cm


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