Transcript Document

Do Now 1.28.15
Pick up a new Do Now sheet.
1. What is a material's index of refraction?
2. What is a lens?
3. Describe the shapes of a concave lens and a convex
lens.
The Human Eye
You see objects when a process occurs that involves both
your eyes and your brain.
Light Enters the Eye
Light enters the eye through the transparent front surface
called the cornea.
The cornea protects the eye.
The pupil is an opening through which light enters.
In dim light, the pupil gets larger; in bright light, the pupil gets
smaller.
The iris is a ring of muscle that contracts and expands
to change the size of the pupil.
It gives the eye its color.
Most people have brown irises; in others, it is blue,
green, or hazel
An Image Forms
After entering the pupil, light passes through a convex
lens.
Ciliary muscles hold the lens in place behind the pupil.
Distant object = muscles relax; lens becomes longer and
thinner
Nearby object = muscles contract; lens becomes shorter
and fatter
When the cornea and the lens refract light, an upsidedown image forms on the retina - layer of cells that
lines the inside of the eyeball
Made up of light sensitive cells called rods and cones.
Rods - contain a pigment that responds to small
amounts of light
Cones - respond to color
A Signal Goes to the Brain
The rods and cones send signals to brain along a short,
thick nerve called the optic nerve.
Begins at the blind spot - an area of the retina with no rods
or cones
Combines the images from each eye into a single 3D image
Correcting Vision
Concave lenses are used to correct nearsightedness.
Convex lenses are used to correct farsightedness.
Nearsighted - person can see nearby things clearly, but
objects at a distant are blurred.
Farsighted - see distant objects clearly, but nearby objects
appear blurry