Download Lesson 2: Reflection and Mirrors (page 322)

Lesson 2: Reflection and Mirrors (page
322)
• Key Questions:
– 1. What are the Kinds of Reflection?
– 2. What types of Images Do Mirrors Produce?
• Sunshine Standards:
– SC.7.P.10.2: Observe and explain that light can be
reflected, refracted, and/or absorbed.
What are the kinds of reflection?
• Do you know why you can see your reflection
in a mirror and not in your textbook?
• To understand this you need to understand
how a surface reflects lights.
What are the kinds of reflection?
• To show how light reflects, you can represent
light waves as straight lines called rays.
• You may already know that light obeys the law
of reflection: the angle of reflection equals the
angle of incidence.
What are the kinds of reflection?
• The two waves in which a surface can reflect
light are regular reflection and diffuse
reflection.
Regular Reflection
• This occurs when parallel rays of light hit a
smooth surface.
• All the light rays reflect at the same angle
because of the smooth surface. So you can
see a clear image.
Regular Reflection
• An Image is a copy of the object formed by
reflected or refracted light rays.
• Shiny surfaces such as metal, glass, or calm
water produce regular images.
Diffuse Reflection
• This type of reflection
occurs when parallel rays
of light hit an uneven
surface.
• Each light ray obeys the
law of reflection, but hits
the surface at a different
angle because the surface
is uneven. Therefore, each
ray reflects at a different
angle.
Diffuse Reflection
• You either don’t see an image, or the image is
not clear.
• Most objects reflect light diffusely. This is
because most surfaces are not smooth.
What types of images do mirrors
produce?
• Plane mirror: a flat sheet of glass that has a smooth silver
colored coating on one side.
• Often, the coating is on the back, and protects the mirror
from damage. The light hits the coating and regular reflection
occurs, this occurs because the coating is smooth.
Virtual Images
• The image you see in a plane mirror is a virtual
images.
• This is an image that forms where light seems to
come from.
• “Virtual” describes something that does not
really exist. Your image appears to be behind the
mirror, but you cannot reach behind the mirror
and touch it.
Plane Mirror
• A plane mirror produces a virtual image that is
upright and the same size as the object.
• But the image is not quite the same as the
object. The left and right of the image are
reversed.
Concave Mirror
• A mirror with a surface that
curves inward like the inside of
a bowl.
• A concave mirror can reflect
parallel rays of light so that they
meet at a point. These rays are
also
parallel to the optical axis.
Concave Mirror
• The optical axis is an imaginary line that
divides a mirror in half.
• The point at which the rays parallel to the
optical axis reflect and meet is called the focal
point.
Concave Mirror
• The type of image formed by a concave mirror
depends on the location of the object.
• Concave mirrors can produce real or virtual
images.
• A real image form when light rays actually
meet.
Real Images in Concave Mirrors
• If the object is farther away from the mirror than
the focal point, the reflected rays form a real
image.
• Unlike a virtual image, a real image can be
projected on a surface such as a piece of paper.
Real images are upside down.
• A real image may be smaller, larger, or the same
size as the object.
Virtual Images is Concave Mirrors
• If an object is between the mirror and the
focal point, the reflected rays form a virtual
image.
• Virtual images formed by a concave mirror are
always larger than the object.
• Concave mirrors produce the magnified
images you see in a makeup mirror.
Convex Mirror
• A mirror with a surface that curves outward is called the
convex mirror.
• The reflected rays spread out but appear to come from a focal
point behind the mirror.
• The focal point of a convex mirror is the point from which the
rays appear to come.
Convex Mirror
• A convex mirror
produces a virtual
image that is always
smaller than the
object.
• These are the types of
mirrors used in “rearview” mirrors on cars.
The advantage to this
type of mirror is that it
allows you to see a
larger area than you
can with a plane
mirror.
Convex Mirror
• The disadvantage is that the image is reduced
in size, and therefore appears farther away
than it actually is.
Lesson 3: Refraction and Lens
• Key Questions:
– 1. What happens when light hits an object?
– 2. What determines the type of image formed by a
lens?
– 3. What factors affect the speed of a wave?
• Sunshine Standards:
– SC.7.P.10.2: Observe and explain that light can be reflected, refracted, and/or
absorbed.
– SC.7.N.1.6: Explain that empirical evidence is the cumulative body of observations
of a natural phenomenon on which scientific explanations are based.
– SC.7.N.1.7: Explain that scientific knowledge is the result of a great deal of debate
and confirmation within the scientific community.
– SC.7.N.2.1: Identify an instance from the history of science in which scientific
knowledge has changed when new evidence or new interpretations are
encountered.
What happens when light hits an
object?
• An object can absorb
some or all of the light
that hits it. An object
can also bend the light
that passes through it,
creating double images
or rainbow.
• When light hits an
object, it can be
reflected , refracted,
and/or absorbed.
What happens when light hits an
object?
• The more transparent
an object is, the less
light it will absorb. An
opaque object will
both reflect and
absorb light.
• The light may also
refract or reflect.
Refraction
• Refraction can cause you to see something
that may not actually be there.
• Example of The Fish Tank: A fish tank can play
tricks on your eyes. If you look through the
side of the fish tank, the fish seems closer
than if you look at it from the top. If you look
through the corner of the tank, you may see
the same fish twice. How does this happen?
Refraction
• As you look at the fish through the tank, the light
coming from the fish to your eye bends as it passes
through three different mediums. The mediums are
water, the glass of the tank, and air.
• As the light passes through the mediums, the light
is refracted.
• When the light rays enter a new medium at an
angle, the change in speed causes the rays to bend.
Reflection in Different Mediums
• Some mediums bend light more than others.
When light passes from one medium into
another, the light slows down.
• Light slows down again and bends even more
when it passes from water to glass.
• When light passes from glass back into air, it
speeds up.
Reflection in Different Mediums
• Notice from the next
figure, that the ray that
leaves the glass is
traveling in the same
direction as it was before
it entered the water.
• Glass causes light to bend
more than either air or
water. Another way to
say this is that glass has a
higher index of refraction
than either air or water.
Refraction in Different Mediums
• The index of refraction
of a medium is a
measure of how much
a light ray bends when
it enters the medium.
• The higher the index
of refraction of a
medium, the more it
bends light.
Prisms and Rainbow
• Recall that when white light enters a prism, each wavelength is
refracted by a different amount. The longer the wavelength, the
less the wave is bent by a prism.
• Red, with the longest wavelength, is refracted the least. Violet,
with the shortest wavelength, is refracted the most.
Prisms and Rainbows
• The difference in refraction causes the white light to spread
out into the colors of the spectrum. The same process
occurs in water droplets.
• When the sun shines through the droplets suspended in
the air, a rainbow may appear. The water droplets act like
tiny prisms. Refracting and reflecting the light and
separating colors.
Mirage
• A mirage is an image of distant object caused
by refraction of light.
Mirage
• In this image you can see what appears to be the a reflection of the truck
in the road. The air just above the road is hotter than the air higher up.
• Light travels faster in hot air, so light rays from the truck that travel
toward the road are bent upward by the hot air. Your brain however,
assumes they travel in a straight line. The rays look like they have
reflected off a smooth surface, but really you are seeing a mirage.
What determines the type of image
formed by a lens?
• A lens is a curved piece of glass or other
transparent material that refracts light.
• A lens forms an image by refracting light rays
that pass through it. Lenses can have different
shapes.
• The type of image formed by a lens depends
on the shape and position of the object.
Concave Lens
• A concave lens is thinner in the center than at the
edges.
• When light rays traveling parallel to the optical
axis pass through a concave lens, they bend away
from the optical axis and never meet.
• A concave lens always produces a virtual image
that is upright and smaller than the object.
Concave Lens
• This figure shows how a concave lens forms an
image. The image is located where the light
rays appear to come from.
Convex Lens
• A convex lens is thicker in the center than at the
edges.
• As light rays parallel to the optical axis pass
through a convex lens, they are bent towards the
center of the lens. The rays meet at the focal
point of the lens and continue to travel beyond.
• The more curved the lens is, the more it refracts
light. A convex lens acts like a concave mirror,
because it focuses rays of light.
Convex Lens
• An object’s position relative to the focus point
determines whether a convex lens forms a
real or virtual image.
Convex Lens
• When an object is between the lens and the
focal point, the refracted rays form a virtual
image. The image forms on the same side of
the lens as the object, and is larger than the
object (like a magnifying glass on a book.)
Convex Lens
• If the object is outside of the focal point, the
refracted rays form a real image on the other
side of the lens. The real image can be smaller,
larger, or the same size as the object.
What Factors Affect the Speed of a
Wave?
• Waves move at different speeds through different
mediums.
• The speed of a wave through a substance is
determined by the substance’s physical properties.
• Light, like all electromagnetic waves, consists of
vibrating electric and magnetic fields. The speed of
light through a medium depends on how the medium
interacts with electric and magnetic fields.
What factors affect the speed of a
wave?
• Some substances will cause the light to move
at a slower speed that it will through other
substances.
• If the speed of light is the same in two
substances, light will not refract when it
passes between these substances.
Factors that affect the speed of a
wave…
Sound Waves
• Sound waves also travel at different speeds
through different substances.
• Temperature is one factor that can affect the
speed of sound.
Sound Waves and Temperature
• The speed of sound in air is about 344 m/s at
room temperature. As temperature increases,
the speed of sound in air also increases. For
solids, however, temperature increase causes
the wave’s speed to decrease.
Sound Waves
• Two factors that determine the speed of sound
through a substance are the compressibility and
density of that substance.
• If either the compressibility or the density of a
substance increases, the speed of sound through
that substance will decrease. When comparing
the speeds of sound through two different
substances, both compressibility and density
must be considered.
Seismic Waves
• The same thing happens with seismic waves. They travel
under the Earth’s surface. Their speed is affected by the
density and compressibility of the material they pass through.