a. The near point of a hypermetropic person is 75 cm from the eye. What is the power of the lens required to enable the person to read clearly a book held at 25 cm from the eye?
b . In what way does the corrective lens help the above person? Does the lens magnify objects held near the eye ?
c. The above person prefers to remove the spectacles with looking at the sky. Explain why .

Explanation

u = -25 cm , u = -75 cm
`(1)/(f) = (1)/(25) - (1)/(75) `, i.e, f = 37.5 cm
The corrective lens needs to have a converging power of + 2.67 dioptres.
b . The correctively lens produces a virtual image (at 75 cm ) of an object at 25 cm . The angular size of this image is the same as that of the object. In this sense the lens does not magnify the object but merely brings the object to the near point of hte hypermetric eye, which then gets focussed on the retina. However, the angular size is greater than that of he same object at the near point (75 cm ) viewed without the spectacles.
c. A hypermetropic eye may have normal far point. i.e., it may have enough converging power to focus parallel rays from infinity on the retina of the shortened eyeball. Wearing spectacles of converging lenses (used for near vision) will amount to more converging power than needed for parallel rays. Hence the person prefers not to use the spectacles for far objects.