Find out the focal length of power 2.5 D

Calculate the focal length of a corrective lens having power +2.5 D.

Solution: Data: Convex lens, P = +2.5 D, f = ?

P = 1/f

∴ 2.5 D = 1/f

∴ f = 1/2.5D = 0.4m = 40cm

The focal length of the lens is 40 cm.

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Calculate the focal length of a lens, if its power is –2.5 D.

Text Solution

Solution : The power of this lens has minus sign, so it is a concave lens. Calculate the focal length yourself as shown in the above question. The focal length will be,`-40` cm.