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Human Eye and the Colourful World Note Science Class 10

• Human eye is the most important sense organ of our body.
• This enables us to see the colorful world around us.
• The eyeball is almost spherical in shape.
• The diameter of the eyeball is approximately 2.5cm.

Different parts of human eye:

Cornea:

• It is present in the front part of the eye ball.
• It is a thin transparent membrane which is bulged outward.
• Light enter into the eye through cornea.

Iris:

• It is present behind the cornea.
• It is a muscular diaphragm which is circular in shape. Function is to control the size of the pupil, and hence regulate the amount of light entering.
• It is responsible for the color of eye.

Pupil:

• It is present in the center of Iris.
• It is a small circular aperture whose size is variable and adjustable.
• Pupil regulate and control the amount of light entering into the eye.

Eye lens:

• It is a double convex lens which is held in position by cilliary muscles.
• Eye lens is made up of transparent and fibrous tissues.
• Its function is to focus the image of any object on the ratina.

1.How the focal length of Eye lens is changed with the cilliary muscles?

Answer : When the cilliary muscles are reflexed the eye lens becomes thin, this increases the focal length of the eye lens.Thus we are able to see the distant objects clearly.

Cilliary muscles released ->R Increases ->F Increases ->We see the distant objects

When we look at close object the eye lens become thick consequently the focal length of the eye lens decreases.

Cilliary muscles contracts ->R decreases ->F decreases ->We see the nearby objects