SS2 Third Term Physics Lesson Note – Application of Lenses: The Human Eye

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WEEK 6:

TOPIC:  APPLICATION OF LENSES: THE HUMAN EYE

CONTENTS

1. Description of the human eye
2. Eye defects and their corrections
3. Comparison of the human eye and camera

Sub topic 1. Description of the human eye

The human eye is a very sensitive organ of the body, it is protected by a ring of bones or socket, eye lids and eye lashes. The diagram below shows the essential parts of the human eye.

The eye lens focus light entering the eye onto the retina. The ciliary muscle is attached to the eye lens and changes the shape of the lens in accordance with the distance of the object in focus. The retina is a light sensitive area located at the back of the eye. It acts as a screen. The yellow spot on the retina is the most sensitive spot to light. The least sensitive portion is the blind spot. The retina is connected to the brain by the optical nerves. The aqueous humor is the transparent liquid between the lens and the cornea and the vitreous humour is a jelly-like liquid between the lens and the rest of the eye ball. The iris acts as a stop or diaphragm of variable size. The pupil is a circular aperture in the iris. The cornea is the transparent front part of the eye, that serves as a protective covering which refracts most of the light that is entering the eye.

Accommodation is the ability of the eye lens to focus objects at different distances onto the retina. The nearest point at which an object is clearly seen by an eye is known as the near point and the farthest point of clear vision is known as the far point. People with normal vision have the nearest distance at which objects can comfortably be seen at about 25cm from the eye.

Evaluation

1. Mention 5 parts of the human eye
2. Define the term accommodation

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