A $$Plano-convex$$ lens is made of a material of refractive index n. When a small object is placed $$30cm$$ away in front of the curved surface of the lens, an image of double the size of the object is produced. Due to reflection from the convex surface of the lens , another faint image is observed at a distance of $$10$$ cm away from the lens, Which of the following statement (s) $$is(are)true$$?

Question

Infinity Learn · Accepted Answer

Reflecting curved surface behaves as a convex mirror  $$1v+1u=1f$$⇒$$1+10+1-30=1f$$⇒$$f=+15cm$$⇒$$R=2f=30cmFor$$ lens:$$m=ff+u$$ For real image ‘m’ is negative−$$2=ff$$−$$30$$​⇒f−$$30=$$−$$f2$$​⇒$$3f2=30$$​⇒$$f=20cm$$​Lens Makers Formula : $$f=$$ Rμ−$$1=20$$​⇒$$30$$μ−$$1=20$$​⇒μ$$=2.5$$

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