The radii of curvature of a lens are +20 cm and +30 cm. The material of the lens has a refracting index 1.6. Find the focal length of the lens

(a) If it is placed in air, and


(b) If it is placed in water (μ = 1.33).


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Radii of curvature of a lens are:



Refractive index of material == 1.6


Refractive index of water = = 1.33


(a) When lens is placed in air


By using the lens makers’ formula;



 We get;





(b) If it is placed in water (μ = 1.33).


By using the lens makers’ formula;
 we get;






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