The Human Body

Chapter Twenty: Vision and Hearing

• 20.1 The Nervous System

• 20.2 Color Vision

• 20.3 Light and Images

• 20.4 Hearing

20.3 Reflection• Light given off from

objects like a light bulb or the Sun travels in straight lines.

• We can show how light travels using imaginary lines called light rays.

20.3 Reflection• Reflection occurs when light bounces off

of a surface. • Imagine a light ray striking a mirror.

20.3 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.

20.3 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.

20.3 Refraction

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

20.3 Refraction• When light goes from

glass to air, it speeds up, bending away from the normal line.

• This bending effect takes place whenever light slows as it moves from one material into another.

20.3 Refraction• 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.

20.3 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.

20.3 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.

20.3 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.

20.3 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.

20.3 Virtual and real images• 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.

20.3 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.

20.3 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.

Investigation 20B

• How does the human eye form an image?

The Human Eye