1. Unit 7
Light and Vision

2. Vision Every time you see something, light is involved.
Light rays in the room reflect off the page and into your eyes.
The reflected light carries information that allows your brain to form an image of the page.

3. How the eye works The eye is the sensory organ used for vision.
The retina contains light- sensitive cells called photoreceptors.
Photoreceptors convert light into nerve impulses that travel through the optic nerve to the visual cortex of the brain.

4. How the human eye sees color
Light is part of a range of waves called the electromagnetic spectrum.
Color is how we perceive the energy of light.

5. Our eyes have two types of photoreceptors: cone cells and rod cells.
Cone cells respond to color.
Rod cells detect black, white, and shades of gray.

6. How color is perceived
Our eyes work according to an additive color process — three photoreceptors (red, green, and blue) in the eye operate together so that we see millions of different colors.

9. Light waves
Light given off from objects like a light bulb or the Sun travels in straight waves.
We can show how light travels using imaginary lines called light rays.

10. Reflection Reflection occurs when light bounces off of a surface.
Imagine a light ray striking a mirror.

11. Law of Reflection
The incident ray is the light ray that strikes the surface of the mirror.
The reflected ray is the light ray that bounces off the surface of the mirror.
The angle of incidence is always equal to the angle of reflection.

12. Refraction
Refraction is the bending of light as it crosses a boundary between two different transparent materials.
As light passes from one type of matter into another, it will change speed and bend.

13. When a light ray traveling through air enters glass it slows down and refracts, bending toward the normal line.

14. A glass rod in water is a good example of refraction.
The glass rod appears to break where it crosses the surface of the water.
This illusion is created because light is refracted as it travels from air to water.

15. Lenses
A lens is an object that is designed to refract light in a specific way.
Many devices you use contain lenses.
There are two basic kinds of lenses: convex and concave.

16. Convex lenses
Light rays that enter a convex lens parallel to its axis refract and meet at a point called the focal point.
The distance from the center of the lens to the focal point is the focal length.

17. Concave lenses
Light rays that enter a concave lens parallel to its axis refract and spread out as they exit the lens.
The focal point of a concave lens is located on the same side of the lens as the light source.

19. Virtual and real images
In a virtual image, light rays do not actually come together to a focal point to form the image.
They only appear to come together.
Virtual images are illusions created by your eye and brain.

20. In a real image, light from a single point on an object comes back together at a single point in another place to make an image.
A convex lens can form a real image.

21. How the human eye forms an image
The pupil is an opening created by the iris, the pigmented part of the eye.
A ring of muscles causes the iris to open or close to change the size of the pupil.

24. How the human eye forms an image
The lens in your eye has a feature that makes it different from the lenses you use in a science lab.
The lens in your eye is flexible and can change its focal length.

25. Anatomy of the Eye