The radii of curvature of the two surfaces of a lens are 20 cm and 30 cm and the refractive index of the material of the lens is 1.5. If the lens is concave -convex, then the focal length of the lens isA. 24 cmB. 10 cmC. 15 cmD. 120 cm

The radii of curvature of the two surfaces of a lens are 20 cm and 30

1.	The radii of curvature of the two surfaces of a lens are 20 cm and 30 cm and the refractive index of the material of the lens is 1.5. If the lens is concave -convex, then the focal length of the lens isA. 24 cmB. 10 cmC. 15 cmD. 120 cm
Answer» Correct Answer - D (d) The focal length of the lens, `1/f=(mu-1)(1/R_(1)-1/R_(2))` `1/f=(1.5-1)(1/20-1/30)rArr1/f=0.5((30-20)/600)` `or1/f=1/2xx10/600=1/120` or The focal length, f = 120 cm

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The radii of curvature of the two surfaces of a lens are 20 cm and 30 cm and the refractive index of the material of the lens is 1.5. If the lens is concave -convex, then the focal length of the lens isA. 24 cmB. 10 cmC. 15 cmD. 120 cm

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