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प्रश्न
A person wears glasses of power − 2.5 D. Is the person farsighted or nearsighted? What is the far point of person without the glasses?
उत्तर
The person must be near-sighted because the person wears glasses of power –2.5 D.
For a near-sighted person, u = ∞.
Focal length, f = `1/( text/"Power") = 1/ ((-2.5)) = -0.4text/" m" = -40 text/" cm"` The lens formula is given by
`1/v -1/u =1/f`
Putting the values , we get:
`1/v = 1/∞ + 1/((-40))`
⇒ v = -40
So, the far point of the near-sighted person is 40 cm.
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