The radius of concave surface is $$20$$ cm and radius of convex surface is $$10$$ cm. The refractive index of material of lens is $$1.5$$. If image of point object P coincides with it. Find the distance (in$$ $$cm) between object and lens.

Question

Infinity Learn · Accepted Answer

For pure lens,  $$1f1=(1.5$$−$$1)($$−$$120+110)=12($$−$$1+220)=140$$ ∴$$P1=140and$$   For pure mirror,  $$Pm=1fm=1$$−$$5$$  Combination of lens and mirror ∴$$P=Pm$$ − $$2P1=$$−$$15$$−$$120=$$−$$1$$−$$420$$ $$=$$ −$$14$$ So, equivalent mirror is concave mirror of focal length $$4$$ cm. Hence,  object should be at the centre of curvature of equivalent concave mirror i.e $$8$$ cm

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The radius of concave surface is 20 cm and radius of convex surface is 10 cm. The refractive index of material of lens is 1.5. If image of point object P coincides with it. Find the distance (in cm) between object and lens.

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