For a particular simple magnifier a user is able to shift the lens slightly toward or…
PHYSICS · Multi-part · CBSE · Physics · Ray Optics and Optical Instruments · Ray Optics and Optical Instruments
Problem
For a particular simple magnifier a user is able to shift the lens slightly toward or away from a printed page.
(i) Show that, for normal adjustment, the object must be placed at a distance slightly less than the focal length of the lens.
(ii) Derive an expression for the object distance required if the final image is instead formed at the near point D.
(iii) Prove that the difference between the two object distances equals Df2.
(iv) Using f=3.0cm and D=25cm, compute the numerical value of this difference.
(v) Discuss how the smallness of this distance difference supports the claim that the infinity setting offers greater convenience for quick focusing.