Question

a farsighted women has a near point of 1.5m. calculate the focal length of the lens used so that she can read an book held at 25cm​

Answer 1

Answer:f=0.3m(30cm)

Explanation: convex lens should be used for hypermetropia.

Objects placed at 25cm should be displayed at 1.5m

So v=-1.5m

F=?

U=-25cm=-0.25m

1/f=1/v-1/u

1/f=1/-1.5-1/-0.25

1/f=-1/1.5--1/0.25

1/f=-1/1.5+1/0.25

1/f=-10/15+100/25

1/f=-2/3+4

1/f=-2/3+12/3

1/f=12-2/3

1/f=10/3

F=3/10

F=0.3m=30cm