(i) At what distance should the lens be held from the card sheet in order to view the squares distinctly with the maximum possible magnifying power ?
(ii) What is the magnification in this case ?
(iii) Is the magnification equal to magnifying power in this case ? Explain.

Explanation

(i) Maximum magnifying power is obtained when the image is the near point (25 cm).
`therefore" Image distance, "v=-25cm`
`"Focal length, "f=10cm`
`"Using "(1)/(v)-(1)/(u)=(1)/(f)`
`-(1)/(25)-(1)/(u)=(1)/(10)`
`u=-(50)/(7)=-7.14cm`
Magnitude of magnification
`m=(v)/(u)=(-25)/(-7.14)=3.5`
(iii) Magnifying power
`m.(1+(D)/(f))=(1+(25)/(10))=3.5`
Yes, the magnifying power (when the image is produced at 25 cm) is equal to the magnitude of magnification.