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Determine the focal length of the lens m...

Determine the focal length of the lens made up of a material of refractive index 1.52 as shown in the diagram. ( Points `C_(1)` and `C_(2)` are the centers of curvature of the first and second surface).

Text Solution

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This lens is called convexo - concave lens
Give: `n = 1.52, R_(1) = 10 cm and R_(2) = 20`
Lens makers formula. `(1)/(f) = (n-1)((1)/(R_(1))-(1)/(R_(2)))`
Substituting the values.
`(1)/(f)=(1.52-1)((1)/(10)-(1)/(20))`
`(1)/(f)=(0.52)((2-1)/(20))=(0.52)((1)/(20))=(0.52)/(20)`
`f = (20)/(0.52) = 38.46 cm`
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