A plano convex lens, when silvered at its plane surface is equivalent to a concave mirror of focal length $$28$$ cm. When its curved surface is silvered and plane not silvered, its equivalent to concave mirror of focal length $$10$$ cm then the refractive index of material of lens is $$29$$×n. Calculate n

Question

A plano convex lens, when silvered at its plane surface is equivalent to a concave mirror of focal length $$28$$ cm. When its curved surface is silvered and plane not silvered, its equivalent to concave mirror of focal length $$10$$ cm then the refractive index of material of lens is  $$29$$×n. Calculate n

Infinity Learn · Accepted Answer

$$1fnet=$$−$$2f2$$−$$1fmCase$$ $$(1)fnet$$ $$=$$−$$281$$−$$28=$$−$$2fL$$−$$1$$∞⇒$$1fL=1561fnet$$ $$=$$−$$2fL$$−$$1fm1$$−$$10=$$−$$2fL$$−$$1$$−$$R2$$⇒$$1R=92801fL=($$μ−$$1)1R$$⇒μ$$=149$$

The lens

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The lens

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A plano convex lens, when silvered at its plane surface is equivalent to a concave mirror of focal length 28 cm. When its curved surface is silvered and plane not silvered, its equivalent to concave mirror of focal length 10 cm then the refractive index of material of lens is 29×n. Calculate n

1fnet=−2f2−1fmCase (1)fnet =−281−28=−2fL−1∞⇒1fL=1561fnet =−2fL−1fm1−10=−2fL−1−R2⇒1R=92801fL=(μ−1)1R⇒μ=149

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