(a) Explain working of human eye.
(b) A person suffering from long sightedness cannot see objects before 1.5 m distinctly. Suggest a lens
with proper focal length and power for his remedy. Assume the near point of the normal eye to be
25 cm.
Answers
Human eye : working and eye defects
Explanation:
Human eye
Eye is located in eye socket. The outer layers are scleroid and choroids.
- Cornea
It is outer exposed part of eye, white in colour, its function is to absorb light and protect eye.
- Iris
i) it holds the pupil
II) it controls the amount of light entering through pupil by adjusting the size of pupil.
It dim light- pupil widens .
In bright light- pupil shortens.
- Pupil
It is black in colour as it absorb all the rays falling on it.
- Cilliary muscles
It holds the lens also adjust the focal length of lens.
- Convex lens
i) It converge the rays falling on it.
Retina
It is the portion where image is formed.
It has two types of cells
a) Cone Cells that respond to colours
b) Rod cells that respond to intensity of light.
- Yellow spot
It is portion or spot on retina where clear image is formed.
- Blind spot : It is a portion where no image is formed only allows optic nerve to enter.
- Aqueous & Vitreous humor
They are fluid present b/w cornea-lens and lens-retina.
They allow refraction of light and also keep eye moist.
The light when enters the eye , the lens converge it and image is formed on retina .
(b) He is suffering from hypermetropia and is advised to use convex lens in spectacles to correct vision.