1.

A person uses `+ 1.5 D` glasses to have normal vision from `25 cm` onwards. He uses a `20 D` lens as a simple microscope to see an object. Calculate the maximum magnifying power, if he uses the microscope (a) together with his glasses (b) without the glasses.

Answer» Here, `P_(1) = 1.5 D : d = 25 cm`,
`P_(2) = 20 D`
(a) with glasses on
`M = 1 + (D)/(f_(2)) = 1 + (25)/(100//20) = 6`
(b) without glasses, Focal length of glasses,
`f_(1) = (100)/(P_(1)) = (100)/(1.5) = (200)/(3)cm`.
`u = - 25 cm, v = ?`
As `(1)/(v) - (1)/(u) = (1)/(f_(1))`
`:. (1)/(v) = (1)/(f_(1)) + (1)/(u) = (3)/(200) - (1)/(25) = (3 - 8)/(200) = (-5)/(200)`
`v = - 40 cm`.
`M = 1 + (v)/(f_(2)) = 1 + (40)/(100//20) = 9`


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