An object is placed 12.9 cm in front of the cornea. (The cornea is thin ans has

Question

An object is placed 12.9 cm in front of the cornea. (The cornea is thin ans has approximately parallel sides so that the reflection that occurs as light travels from air to cornea to aqueous humor is essentially the same as though the aqueous humor were directly in contact with the air. The aqueous humor has index of refraction n = 1.34 and the radius of curvature of cornea is 7.8 mm.)

(a) What is the image distance for the image formed by the cornea alone?____________


(b) The image formed by the cornea serves as an object for the lens. Treat the lens as a thin lens 6 mm behind the cornea. Find the optical power of the lens necessary to form an image on the retina, 21 mm from the center of the lens. ______________

Explanation / Answer

we know that, n1/p+n2/q=(n2-n1)/R

n1= refractive index of medium 1,i.e air=1

n2=refractive index of medium 2=1.34

R=radius of curvature=7.8 mm

p=12.9 cm

so by substtituting,

1/12.9-1.34/q=(1.34-1)/0.78 cm

0.0775/cm-1.34/q=0.435 /cm

q=3.738 cm

b)1/p+1/q=1/f

21 mm is the new image, p=2.1 cm

object distance=3.738 +0.6 mm=4.33 cm

So,1/f=1/2.1+1/4.33

f=1.415 cm

Power=1/f=0.7066 /cm

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