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2-3 Reflection and Refraction
I.
Reflection
Reflection- occurs when an object or wave bounces back off a
surface through which it cannot pass.
Law of Reflection- all waves obey this law.
1. The angle of incidence equals the angle of reflection.
II. Mirrors
1. There are 3 types of mirrors: Plane, concave, and convex.
A. Plane Mirrors:
1. Plane mirrors- flat sheet of glass that has a smooth, silvercolored coating on one side.
When light strikes a mirror, the coating reflects the light
forming an image.
2. Image- a copy of an object formed by reflected or refracted
rays of light.
3. Plane mirrors produce a virtual image.
4. Virtual Image- an upright image that forms where light seems
to come from. The image appears to behind the mirror.
B. Concave Mirrors:
1. Concave mirror- a mirror with a surface that curves inward like
the inside of a bowl.
2. Optical Axis- imaginary line that divides a mirror in half.
3. Focal Point-The point at which rays parallel to the optical axis
meet.
4. The more curved the mirror the closer the focal point is.
5. Concave mirrors can form either virtual or real images.
a. If an object is farther away from the mirror than the focal
point the reflected rays form a real image.
b. Real image- forms when rays actually meet.
6. Virtual images formed by a concave mirror are always larger
than the object.
C. Convex Mirrors:
1. Convex Mirror- a mirror with a surface that curves outward.
2. Rays never meet in a convex mirror thus forming images that
are virtual and smaller than the object.
3. Convex mirrors can never create a real image.
4. Used in passenger side car mirrors, security mirrors and safety
mirrors.
5. Objects appear farther than they actually are.
III. Refraction
Refraction- bending of light waves due to a change in speed is
known as refraction.
A. Refraction in Different Mediums
1. When light rays enter a medium at an angle, the change in
speed causes the rays to bend, or change direction.
2. Stars appear to shimmer because that path of light is not a
straight line.
B. Effects of Refraction
1. A prism causes the white light to spread out into the colors of
the spectrum.
2. Water droplets act like tiny prisms separating the white light
into the different colors forming a rainbow.
3. Occurs when placing a pencil in a glass of water, the light
coming from the pencil to your eyes bends as it passes through
3 different mediums.
IV.
Lenses
1. Lens- a curved piece of glass or other transparent material
that refracts light.
2. Used in telescopes, microscopes, and cameras.
A. Convex Lenses
1. Convex lens- or magnifying glass is thicker in the center than at
the edges.
2. The more curved a lens the more it refracts light.
3. Convex lenses focus rays of light.
4. An objects position relative to the focal point determines
whether a convex lens forms a real image or a virtual image.
B. Concave Lenses
1. Concave lens- is thinner in the center than at the edge.
2. A concave lens can produce only virtual images because
parallel light rays passing through the lens never meet.