Question

For a normal eye, the far point is at infinity and the near point of distinct vision is about 25cm in front of the eye. The cornea of the eye provides a converging power of about 40 dioptres, and the least converging power of the eye-lens behind the cornea is about 20 dioptres. From this rough data estimate the range of accommodation (i.e., the range of converging power of the eye-lens) of a normal eye.

Answer 1

Given :

Least distance of distinct vision = d= 25cm

Far point = normal eye=d1=∞

Converging POWER of cornea=Pc= 40D

Least converging power of eye lens =Pe=20D

To see the objects at Infinity , the eye needs least converging power.

Power of the eye lens =P= Pc+Pe

=40+20=60 D

Power of eye lens= 1/f ocal length of eyelens

F=1/P

=1/60D

=100/60=5/3 cm

To focus an object at the near point,

object distance (u) = −d = −25 cm

Focal length of the eye-lens = Distance between the cornea and the retina = Image distance  

Image distance=v=5/3 cm

Lens formula :

1/f1= 1/v-/1u

1/f1= 3/5+1/25

=15+1/ 25

=16/25/cm

P1=100/f1

=16x100/25

=64D

Power of eye lens= 64- 40=24D

Range of accommodation of eye lens= 20 D to 24D

Answer 2

Explanation:

.............................