i) Power lenses are required to see distant objects
1/f = 1/v – 1/u
1/f = 1/10
f = -10 cm = -0.1 m
P = 1/f
P = 1/(-0.1)
P = -10 diopter
ii) When no corrective lens used
Pn = Pf + Pa
u = -10 cm = -0.1 m
v = 2 cm = 0.02 m
1/f = 1/v – 1/u = 60
Pn = Pf + Pa = 64 D
u = xn
xn = 1/14 m = 100/14 cm = 7 cm
iii) When used corrective lens
u = infinity
v = 2 cm = 0.02 m
1/f = 1/v – 1/u
P = 50
Pn = 50 + 0
Pn = 50 D
u = xnm
xm = ¼ m = 0.25 m