Bellringer
What color would a basketball appear
to be if under an orange flashlight?
What color would it appear to be if
under a red flashlight?
Light
Part II
Concave Mirrors
• Concave mirrors can form either virtual
images, or real images.
• A concave mirror is a mirror that
curves inward like the inside of a bowl
(think: cave-in). A concave mirror
reflects light rays toward the center of
the mirror. The light rays all meet at the
same point, called a focal point.
Concave Mirrors
•
•
The image formed by a concave mirror is
either a virtual image or a real image.
This type of image depends on where the
object is placed.
A concave mirror forms a virtual image if
the object is farther from the mirror than
the focal point. (Remember, a virtual
image is an upright image that seems to
form behind the mirror.)
Virtual Image from
Concave Mirror
Concave Mirrors
• A concave mirror forms a real image if
the object is farther from the mirror than
the focal point. A real image forms
when reflected light rays actually meet.
A real image forms in front of the mirror.
A real image is always upside down.
Real Images from
Concave Mirrors
Convex
Mirrors
• Because the rays never meet, images
formed by convex mirrors are always
virtual and smaller than the object.
• A convex mirror is a mirror with a
surface that curves outward like the
outside of a bowl. A convex mirror
reflects light rays outward. The reflected
rays spread out and never meet.
However, the rays seem to be coming
from a point beyond the mirror. The
image looks as though it is behind the
mirror.
Convex Mirrors
• Convex mirrors are used in cars as side
mirrors.
• “Objects in mirror are closer than they
appear.”
• Convex mirrors let you see a bigger
area then other mirrors do. The
compromise here is that it reduces the
apparent size of the object being
reflected.
Refraction of Light
•
•
•
When light rays enter a medium at an angle,
the change in speed causes the rays to
bend, or change direction.
Light travels at different speeds in different
mediums.
When light passes from air into water at an
angle, one side of the light rays slows down
before the other side. This causes the light
to bend, or refract.
Refraction of Light
• How much a medium causes light to
slow down and bend is the medium’s
index of refraction. Air has an index of
refraction of 1.00. Water has an index of
refraction of 1.33. The higher the index
of refraction, the more light slows down
and bends.
Refraction of Light
• Remember, white light is made up of
light of different wavelengths. When
light enters a medium (prisms, water
droplets, etc.) at an angle, longer
wavelengths of light slow down and
bend less than shorter wavelengths.
The light separates into different colors.
This is why sunlight may form a rainbow
when it passes from air into raindrops.
Lenses
•
•
•
An object’s position relative to the focal point
determines whether a convex lens forms a real
image or a virtual image. A concave lens can
produce only virtual images because parallel
light rays passing through the lens never meet.
A lens is a curved piece of glass that is used to
bend light.
A lens forms a virtual image or a real image.
The type of image depends on the shape of the
lens and the position of the object.
Lenses
• A convex lens is thicker in the center
than at the edges. A convex lens bends
light rays toward the center of the lens.
All the rays pass through the focal point.
• The image formed with a convex lens
can be a real image or a virtual image. If
the object is farther from the lens than
the focal point, a real image forms. If the
object is closer to the lens than the focal
point, a virtual image forms.
Lenses
• A concave lens is thinner in the center
than at the edges. A concave lens
bends light away from the center of the
lens. The light rays never meet, so the
image is always a virtual image. The
image is upright and smaller than the
object.