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
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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
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