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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