light is represented as a straight line or ray that shows the
direction the light wave is travelling. Remember that light is made
up of waves and can be described using wavelength and
frequency.
Slide 4
Transparent a material that allows light to pass through
freely. All or most of the light is transmitted. Translucent a
material, such as frosted glass, that lets most light rays through,
but scatters them. Some light is transmitted. Opaque a material
that prevents any light from passing through. All or most of the
light is absorbed or reflected.
Slide 5
Slide 6
Transparent? Translucent Opaque
Slide 7
You can use the ray model to predict where shadows will form
and how large they will be. The closer the object is to the light
source the larger the shadow. The further the object is from the
light source the smaller its shadow will be. No shadow can be
perfect*
Slide 8
Slide 9
If a wave strikes the sea wall on an angle how will it bounce
off? ** precisely the same angle Incident ray= incoming ray
Reflected ray= ray that bounces off barrier Normal= dotted line
perpendicular to the boundary between two materials. Drawn at right
angles to the solid barrier Angle of incidence= formed by incident
beam and normal Angle of reflection= formed by the reflected beam
and normal Why is it called the Law of Reflection? ** angle of
reflection = angle of incidence
Slide 10
Normal line
Slide 11
Slide 12
When light moves into a medium of higher density it slows down
(i.e. air to water, or air to glass) and moves towards the normal
line.
Slide 13
When light moves into a medium of lower density it speeds up
(i.e. water to air or glass to air) and bends away from
normal.
Slide 14
Slide 15
Slide 16
Bowl of Water Place a coin at the bottom of a bowl/cup. Step
back until the coin just stops being visible over the lip of the
bowl/cup. Then have someone slowly pour water into the bowl. What
do you see? Why does this happen? Pencil Insert a pencil at an
angle into the cup. Try looking at the pencil at different angles
(above and below the water line). What do you see? Does anything
change, or stay the same? Why? Vegetable Oil and a Cup Put the shot
glass inside the larger glass. Fill the larger glass with water.
Just enough to cover the smaller glass by an inch Look at the glass
from different angles. Do you see the drinking glass? Why? Spill
out the water and dry the shot and larger glass. Put the shot glass
back inside the larger glass Fill the larger glass with cooking
oil. Look at the glass from different angles. Do you see the
drinking glass? Why? Pour the vegetable oil back into the plastic
cup. Dry and clean both glasses for the next group.
Slide 17
Bowl of Water When the bowl is empty the edge of the bowl stops
you seeing the coin. When the bowl is full of water the light bends
over the edge so you can see the coin. Have you ever noticed that
things at the bottom of a pool or river always look closer to the
surface than they really are? This is because of the way light is
bent through water and is an effect of refracted light. Pencil From
above, the pencil seems to bend at the water line because
refraction has occurred between the two mediums of water-air. The
pencil also looks bigger underwater. This is because of the glass
has curved surfaces and therefore the water in it acts as a convex
lens. Vegetable Oil and a Cup As light passes through one medium to
another (water-air, glass-air), the light is bent (refracted) at
the boundary between the two mediums. This happens because light
travels at different speeds through different mediums. Light moves
through petroleum products (including cooking oil) at about the
same speed as it does through the glass. Therefore, as light passes
between glass and oil it doesnt bend at the boundaries, leaving the
boundaries invisible.
Slide 18
Slide 19
Refraction of light can also occur when light travels through
air at different temperatures. Warm air is less dense than cooler
air. When light enters cooler air it will slow down and bend
towards normal.
Slide 20
Mirage of water on pavement on a hot summer day. How does this
happen?
Slide 21
Answer: Air close to the pavement becomes superheated. As light
travels from the road to your eye, it slows down when it hits the
cooler air above the highway. It will slow down and bends towards
normal. The effect causes a water mirage.
More or less than meets the eye. A real image is one in which
light rays actually come from the image. In a virtual image, they
appear to come from the reflected image - but do not. In a flat
mirror, for example, the virtual image of an object is behind, or
"inside" the mirror, but light rays do not originate from there.
Real images form outside the system, where emerging light rays
cross and are "caught"...inside camera...on a screen...or in a
Mirage. All concave mirrors can produce real images under certain
circumstances.
Slide 24
Slide 25
Slide 26
Plane Mirrors All mirrors reflect light according to the law of
reflection. Plane mirrors form an image that is upright and appears
to be as far behind the mirror as the object in front of it
is.
Slide 27
Plane mirrors produce an image with the same orientation as
well. Take a look at this video...
http://www.youtube.com/watch?v=H_Dtsx-
VGG0http://www.youtube.com/watch?v=H_Dtsx- VGG0
Slide 28
Slide 29
Concave mirrors curve inward. They can form an image that is
inverted or right side up, and can be larger or smaller than the
object. Parallel light rays bounce off the curved surface and meet
at a single point called the focal point. We describe the lights
rays joining together as converging. Objects distance to focal
point of mirror: far= small and upside down image. Close= remains
inverted, but larger. If the object is between the focal point and
the mirror=object is larger and upright.
Slide 30
Slide 31
Slide 32
Spotlights Flashlights Lighthouses Car headlights (bright light
is placed at focal point)
Slide 33
Convex mirrors bend outwards. Remember the question about why
objects in mirror are closer than they appear? 1. The image is
smaller than the object. 2. The image distance is smaller than the
object distance. 3. The image is upright. 4. More can be seen in
convex mirror opposed to a plane mirror. They reflect parallel
light rays as if they came from the focal point behind the mirror.
The light rays do not meet. Instead, they diverge (spread a part
after reflecting).
Slide 34
Slide 35
Which mirror is best suited for security purposes in retail
stores and why? (Plane, concave or convex?)
Slide 36
Materials: Ray box, concave/convex lenses, and a printed page
1) Shine the ray box at a concave lens. Observe how the rays are
affected. Draw your observations 2) Look through the concave lens
at some printed text. Observe the appearance of the print. Draw
your observations 3) Shine the ray box at the convex lens. Observe
how the rays are affected. Draw your observations. 4) Look through
the convex lens at some printed text. Observe the appearance of the
print. Draw your observations. Compare what you observed about the
appearance of the text with each of the two lenses. Which type of
lens would be best used as a magnifying glass? What might the other
kind of lens be used for?
Slide 37
Concave lenses are thinner in the middle than at the edge.
Light rays that pass through a concave lens diverge The rays never
meet at focal point and always bend outwards.
Slide 38
Concave lenses work to make something look smaller, so they're
not quite as common as convex (magnifying) lenses. Telescopes
Binoculars Eyeglasses
Slide 39
Convex lenses are thicker in the middle of the lens and they
thin out towards the edges. When light rays pass through they
converge and meet at a focal point. When light rays passes through
the center it continues in a linear path. When light rays passes
through the more curved sides, they refract, i.e. Bend Images seen
through convex lenses are larger than concave images.
Slide 40
Slide 41
Eyeglasses Magnifying glass
Slide 42
Convex lenses and concave mirrors both reflect light rays that
converge at the focal point Like concave mirrors, convex lenses
also produce reflective images that are either smaller/ larger, or
upright/inverted to the object itself. The objects position to the
focal length and lens will determine the image produced.
Slide 43
Explain why a drop of water placed on the page of a book
magnifies printing beneath it.