Question

the near point of a person suffering from hypermetropia is at 50 cm from his eye . what is the power of the lens needed to correct this deflect.

Answer 1

Person suffering from long sightedness. so near point is 50 cm and far point is infinity.
convex mirror is required to correct this defect.
v =50cm
u=-infinity
1/f=1/v-1/u
1/f=1/50-1/-infinity=1/50
f=50cm =0.5m

power=1/focal length
=1/0.5=10/5=2D

Answer 2

Hello john,
.
Here is ur solution
.
It will........... Help
.
v = - 50 cm 

u = -25 cm

Using lens equation, 

1/f = 1/v -1/u 

1/f = -1/50 - 1/(25)

1/f = -1/50 + 1/25 

1/f = 1/50 

P = 1/f (in m) = 100/50 = 2 D

Therefore power of conex lens needed to correct this deflection is 2D
____________________________
___________________________