A converging beam of light converges towards a point $$20$$ cm behind an equiconvex lens placed in the path of the beam. After refraction through the lens, the beam converges at a distance of $$10$$ cm from the lens. If refractive index of glass is $$1.5$$, find the radius of curvature of the curved surfaces of the lens.

Question

Infinity Learn · Accepted Answer

$$1+10$$−$$1+20=1f$$⇒$$1f=120$$⇒$$f=20$$ cmNow, $$2$$μ−$$1R=1f$$⇒$$R=2$$μ−$$1f=21.5$$−$$1$$×$$20$$ cm⇒$$R=20$$​ cm

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