Question

the near point of a person is at 75 cm from his eye. find the power of lens which he requires to read clearly a book held at a distance of 25 cm from the eye​

Answer 1

1/0.75=4/3
=1.33 hoga right answer

Answer 2

1/f = 1/v - 1/u

f = focal length, v = image distance = -75 (in this case) & u= object distance = -25 (in this case)

therefore, (1/-75) - (1/-25) = 1/f

⇒ -1/75 - (-1/25) =1/f

⇒ -1+3/75 = 1/f

⇒2/75 = 1/f

∴ f = 75/2 = 37.5 cm = 0.375 m

Power of lens, 'P' = 1/f (f in meters)

⇒ P = 1/0.375 =  + 2.66 D