A person wears glasses of power `- 2.5 D`. Is the person short sighted or long sighted ? What is the far point of the person without glasses ?
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Here, `P = - 2.5 D` As `P` is negative, the person is short sighted `f = (100)/(P) = (100)/(- 2.5) = - 40 cm` An object at infinity from the corrective lens must produce the virtual image at the far point, i.e., From `(1)/(v) = (1)/(f) + (1)/(u) = (1)/(- 40) + (1)/(oo)` `v = - 40 cm`
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