Transcript 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.

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
The Human Eye
• How does the human eye form an image?