(a) Calculate maximum power of accommodation of a person having normal vision. (b) A person needs to use…
(a) Calculate maximum power of accommodation of a person having normal vision.
(b) A person needs to use glasses for reading newspaper. Identify the defect in her vision and the type of lens she would need to correct it.
(c) Sometimes when we enter into a dark room from bright sunlight we are unable to see objects clearly. Why?
Solution
(a) For a normal eye the least distance of distinct vision is $D = 25\ \text{cm}$.
$P = \dfrac{100}{f\ (\text{cm})} = \dfrac{100}{25} = 4\ \text{D}$
So the maximum power of accommodation of a normal eye is $4\ \text{D}$.
(b) The defect is **hypermetropia (far-sightedness)**; it is corrected using a **convex lens**.
(c) In bright light the pupil contracts and becomes small to limit the light entering the eye. On entering a dark room the pupil needs some time to expand again so that more light can enter, and until then objects are not seen clearly.