Question

A woman can read the large print in a newspaper only when it is at a distance of 55 cm or more from her eyes.

Answer 1

Answer:

Farsightedness (hyperopic)

2.79 D

Explanation:

When a person cannot see something which is close to their eyes this condition is known as farsightedness. She should use a convex lens to correct her eye sight.

u = Object distance =  22-2.7 = 19.3 cm

v = Image distance = -55+2.7 = -52.3 cm

f = Focal length

$\frac{1}{f}=\frac{1}{u}+\frac{1}{v}\\\Rightarrow \frac{1}{f}=\frac{1}{19.3}+\frac{1}{-52.3}\\\Rightarrow \frac{1}{f}=\frac{3300}{100939}\\\Rightarrow f=\frac{100939}{3300}=30.58\ cm$

The power of a lens is given by

$P=\frac{1}{f}\\\Rightarrow P=\frac{1}{0.358}=2.79\ D$

The power of her glasses should be 2.79 D