The least distance of vision of a longsighted person is 60 cm. By using a spectacle lens, this distance is reduced to 12 cm. The power of the lens is
+ 0.5 D
+ ( 20/30 ) D
(10/3) D
+ 2.0 D
B.
+ ( 20/30 ) D
Using:-
By using mirror equation
where,
u - object distance
v - image distance
f - focal length
Here v = 60 cm
u = 12 cm
∴
=
=
⇒ f = 15 cm
Power P =
P = D
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