Light ppt

1. Where doWhere do
we getwe get
light?light?

2. A luminous object is one that produces light.
An illuminated object is one that reflects light.
Luminous Objects Illuminated Objects
Luminous andLuminous and
Illuminated ObjectsIlluminated Objects

3. We see things because they
reflect light into our eyes:
Homework

4. How does light behave?How does light behave?

5. ReflectionReflection of Lightof Light
• Reflection occurs when a
wave bounces back after
striking a barrier.
• Example: a reflection in
a mirror.

6. Three things that affect howThree things that affect how
light is reflected:light is reflected:
• Surface of
the Object
• Color of the
Object
• Shape of the
Object

7. Clear vs. DiffuseClear vs. Diffuse
ReflectionReflection
Smooth, shiny surfaces
have a clear reflection:
Rough, dull surfaces have
a diffuse reflection.
Diffuse reflection is when
light is scattered in
different directions
Surface of the Object

10. Ever notice that an
asphalt driveway seems
hotter on a summer day
than a concrete
sidewalk?
This occurs because light
that is not reflected
from the surface of an
object may be absorbed
by the object and
converted into thermal
energy.
Color of the Object

11. ShapeShape of the Objectof the Object
Reflection from a mirror:
Incident ray
Normal
Reflected ray
Angle of
incidence
Angle of
reflection
Mirror

12. The Law of ReflectionThe Law of Reflection
Angle of incidence = Angle of reflectionAngle of incidence = Angle of reflection
In other words, light gets reflected from a surface at
____ _____ angle it hits it.
The
same !!!

14. Types of MirrorsTypes of Mirrors
Plane (flat), Concave, & Convex

15. Plane MirrorsPlane Mirrors
• Flat Surface
• Light is
reflected
straight back,
resulting in an
upright image
that is the same
size as the
original object.

16. •Mirror LabMirror Lab
• Read and follow directions for Flip-Flopped
Messages to investigate plane mirrors.
• When Completed create a five word
message for a partner using the mirrors.
• Have partner decodes.
• Using mirrors is fun.
• Justify the Law of Reflection
Using the plane mirror.
HINT: Think about angles….

17. Concave MirrorsConcave Mirrors
• Curves Inward (like
the inside of a bowl)
• If an object is very
close to the mirror,
light is reflected in a
way that an enlarged,
upright image is
produced.
• If the object is very
far away, the image is
reduced in size and
upside down.

18. Convex MirrorsConvex Mirrors
• Curves Outward
• Results in an image
your eyes detect as
upright and
reduced in size.
• The side mirrors on
cars are convex
mirrors. (Objects
in mirror are closer
than they appear.)

19. SpoonsSpoonsSteps:
1. Look at your reflection on the inside of the spoon.
Record what you see.
The surface on the inside of a spoon bends in like a cave - it is
concave.
Dentist use concave mirrors to examine your teeth. These mirrors
make your teeth look bigger so the dentist can examine them more
easily. Likewise, shaving mirrors are concave because they make
the face look bigger.
2. Now turn your spoon out and look at your reflection on the outside
of the spoon. Record what you see.
The surface on the outside of a spoon bends out - it is convex.
The next time you are at a funfair take a look at yourself in the crazy
mirrors. They bend in all sorts of ways so that you look bigger,
smaller, fatter, thinner and even wavy.
3. Explain why you look different and how these things pertain to the
standard: describe the behavior of light waves Be prepared to
report out.
4. Give examples of what we use every day in our daily lives?
{Hint} With this understanding of convex and concave mirrors.

21. RefractionRefraction of Lightof Light
• Refraction is
the bending of
a wave as it
passes from
one medium to
another.

22. What causes the light to bend?What causes the light to bend?
What’s different about air and water?
DENSITY – the amount of mass in a certain
volume of a substance (mass/volume)
AIR WATER
gas liquid

23. Example of RefractionExample of Refraction
When a straw is placed
in water it looks like
this:
In this case the light rays
are slowed down by the
water and are bent,
causing the straw to look
broken. The two mediums
in this example are air and
water.

24. Another Example:Another Example:
When you use a
magnifying glass, the
object appears larger
because of refraction.
The light waves traveling
in the air change
direction when they
enter the glass of the
lens, and then again
when they move from
the glass back into the
air again.
Lens

25. Introduction of Magnifying GlassIntroduction of Magnifying Glass
I bumped into this week's experiment while washing the dishes.
Lisa had placed a new cartridge for our water filter into a
glass of water to rinse it. When I glanced up, the filter had
swollen until it filled the inside of the glass! It was only
when I lifted the normal sized filter out of the glass that I
realized what had tricked me. To investigate, you will need: a
tall, clear drinking glass
water
your finger, a spoon, a banana, etc.
Place the glass on a flat surface. Looking from the side, stick
your finger into the glass. OK, nothing unusual so far. Now
fill the glass with water. Again, stick your finger into the
glass. Looking from the side, this time you should see a
difference. Your finger looks bigger. Try the same thing
with a large spoon. An object that is about half as wide as
the glass will seem to fill it. Why?
The glass of water acts as a lens to magnify objects inside. The
thin layer of glass alone does not cause the magnification.
You need the water for it to work. Without the water, light
enters the glass and hits your finger. Some of the light is
absorbed, and some is reflected, spreading outwards. Some
of this light hits your eye and you see your finger.

26. With water in the glass, things start the same. Light still reflects
from your finger and spreads outwards. This time as the light
moves from the water to the glass and then to the air, something
happens. Its speed changes. Wait a minute! The speed of light is a
constant, right? 300,000 k/m per second. That speed is for light in
a vacuum. It travels through other substances (air, water, glass,
oil) at different speeds. As it changes speed, if it is traveling
perpendicular to the surface (straight through), nothing much
happens. If the boundary is at an angle to the direction the light is
traveling, the light is bent from its path.
The shape of the surface at the speed change also has an impact on
what you see. If the boundary between two different substances is
flat, then you don't notice much of a difference. The image may be
shifted to the side as the light is bent, but everything looks the
right size. If the boundary is curved, then the image is distorted.
Depending on the shape of the boundary and the speed of light in
each of the substances, the light waves can be spread apart or
bent together. If they are spread outwards, the image looks
bigger. If they are bent inwards, the image looks smaller.
This has other implications besides making fingers look larger. Would a
lens shaped to focus light on Earth (in air) work the same in space?
If you wear eye glasses, do you think they would work well if you
were underwater? For that matter, do your eyes work as well
underwater as in air? What would you see if you were in a room
filled with water and you stuck your finger into a glass of air?

27. DiffractionDiffraction of Lightof Light
Diffraction is
the bending,
spreading, and
interference
of waves when
they go
through a
narrow opening.

28. Diffraction PatternsDiffraction Patterns
• Radio waves can
diffract around hills,
mountains or even
the whole planet.
• Light waves can
diffract through tiny
slits.
• X-rays can diffract
around atoms.

29. Electromagnetic waves have aElectromagnetic waves have a
huge range of wavelengths.huge range of wavelengths.
If the wavelength is of a similar
size to a gap in a harbor wall, then
the wave will diffract as shown
below.

30. If the wavelength does not match
the size of the gap, then only a
little diffraction will occur at the
edge of the wave.

31. TransmissionTransmission of Lightof Light
Transmission is
the passing of
waves through
a medium.

32. Safety Rules for lights andSafety Rules for lights and
PrismPrism
Lights out of eyes
Handle objects with care
http://www.youtube.com/watch?v=NU2r-ECmPr4
http://www.youtube.com/watch?v=NU2r-ECmPr4

33. Prism LabPrism LabSeparating light with a prism experiment
Try It Out Inside the box, place the prism on a sheet of dark
paper. Shine the flashlight beam through the hole and adjust the
prism as shown in the diagram. Use coloured pencils or pens to
trace the individual bands of light that you see. In what order are
the colours? Can you come up with a mnemonic to help you memorise
the sequence of colours in prismatic light?
Make It
In order to create a clearly visible spectrum of light with a prism,
it's best to work in a darkened room with a single source of light. A
cardboard box (such as a file box) makes a great prism box. Simply
cut a small rectangular opening on the side of the box near the
bottom edge, about 5 mm in width.
Experiment
Finally, cut a second hole in the box and arrange two prisms so that
their spectra cross paths. What happens to the various colours of
light where they cross?
You will need:
· A prism (or two)
· A cardboard box (such as a file box)
· Coloured pencils or pens
· A sheet of plain white paper
· A flashlight or reading lamp

34. Questions for Written ReportQuestions for Written Report
Discuss visible light spectrum:
• Explain why does the prism make the spectrum
• How do you make the spectrum narrow or wide?
• When adding double plane mirrors with a prism,
describe what happens with the visible light
spectrum?
• Synthesis the two types of light concepts used
when there are prisms and mirrors in the
experiment.
• Consider a (What if question) using the prisms and
mirrors then analyze your response.

35. Be prepared to Report out your Lab findings
and how they relate to the standard.
S8P4a,bCharaacteristics of the E/M
Spectrum; describe the behavior of light
waves

36. What happens when lightWhat happens when light
hits these objects?hits these objects?
•Glass of water
•School bus window
•Notebook paper
•Waxed paper
•Plastic wrap
•Tissue paper
•Cardboard
•Textbook
•Hand lens…

37. Many materials are classified byMany materials are classified by
how well they transmit light.how well they transmit light.
• Three Types of
Materials:
– Transparent
– Translucent
– Opaque

38. TransparentTransparent
A material
that permits
light to pass
through

39. Transparent objects:Transparent objects:
– The windows on a school bus,
– A clear empty glass,
– A clear window pane,
– The lenses of some eyeglasses,
– Clear plastic wrap,
– The glass on a clock,
– A hand lens,
– Colored glass…
•ALL of these are transparent.
•Yes, we can see through them
because light passes through
each of them.

40. TranslucentTranslucent
A material that
transmits
some light but
also scatter
light in all
directions

41. Translucent objects:Translucent objects:
– Thin tissue paper,
– Waxed paper,
– Tinted car windows,
– Frosted glass,
– Clouds,
•All of these
materials are
translucent and allow
some light to pass
but the light cannot
be clearly seen
through.

42. OpaqueOpaque
A material
that allows
no light to
pass through

43. Opaque objects:Opaque objects:
– Heavy weight paper,
– Cardboard
– Aluminum foil,
– Mirror, bricks,
buildings,
– Your eyelids and hands,
– Solid wood door,
•All of these objects
are opaque because
light cannot pass
through them at all.
•They cast a dark
shadow.

44. Shadows
Shadows are places where light is “blocked”:
Rays of light

45. Compare and ContrastCompare and Contrast
Transparent objects
Translucent objects
Opaque objects
Explain why each group is the type of material and
how they are used in our daily lives.
Be prepared to Report out your answers and how
they relate to the standard.
. S8P4a,b describe the behavior of light waves

46. THANK You
THANK You