Download Let there be light!!!

Let there
be light!!!
Light Energy &
How light interacts with matter
What is light?
• Light is a form of radiant energy that
you can detect with your eyes. Light
energy comes from chemical energy,
electrical energy and nuclear energy.
• Light can pass through anything that is
transparent, sort of passes through
translucent objects (frosted window) but
doesn't make it through opaque objects
such as a brick wall.
Properties of Light
• Light travels in straight lines:
Laser
Light travels VERY FAST – around
300,000 kilometres per second.
At this speed it can
go around the world 8
times in one second.
• Light travels much faster than sound.
For example:
Thunder and
lightning start at
the same time, but
we will see the
lightning first.
We see things because they
reflect light into our eyes:
Homework
Luminous and non-luminous objects
A luminous object is one that produces light.
A non-luminous object is one that reflects light.
Luminous objects
Reflectors
•Sun
•Water
•Light bulbs
•Mirrors
•Fire
•Smooth shiny
surfaces
Shadows
Shadows are places where light is “blocked”:
Rays of light
Properties of Light summary
1) Light travels in straight lines
2) Light travels much faster than sound
3) We see things because they reflect
light into our eyes
4) Shadows are formed when light is
blocked by an object
Reflection
• Reflection from a mirror:
Normal
Reflected ray
Incident ray
Angle of
incidence
Angle of
reflection
Mirror
• The Law of Reflection
Angle of incidence = Angle of reflection
In other words, light gets reflected from a surface at
____ _____ angle it hits it.
The
same !!!
Clear vs. Diffuse Reflection
• Smooth, shiny
surfaces have a
clear reflection:
Rough, dull surfaces
have a diffuse
reflection.
Diffuse reflection is
when light is scattered
in different directions
Using mirrors
• Two examples:
2) A car headlight
1) A periscope
Color
• White light is not a single color; it
is made up of a mixture of the
seven colors of the rainbow.
We can demonstrate
this by splitting white
light with a prism:
This is how rainbows
are formed: sunlight is
“split up” by raindrops.
• A rainbow would form a complete circle,
not just an arc, if the ground didn't get in
the way
• Rainbows always face the observer. As the
observer moves, the rainbow moves.
• And sorry, no one can ever get to the "pot
of gold" at the end of the rainbow
Seeing color
• The color an object appears depends on
the colors of light it reflects.
For example, a red book only reflects red light:
White
light
Only red light
is reflected
A pair of purple shorts would reflect purple light (and
red and blue, as purple is made up of red and blue):
Purple light
A white hat would reflect all seven colors:
White
light
Take a ride on
the Magic School Bus!
Refraction
Refraction is when waves ____ __ or slow down due to
travelling in a different _________. A medium is
something that waves will travel through. When a ruler
is placed in water it looks like this:
In this case the light rays are slowed down by the water
and are _____, causing the ruler to look odd. The two
mediums in this example are ______ and _______.
Words – speed up, direction, water, air, bent
Key Vocabulary
Reflection – The light energy that
bounces off objects.
Refraction – The bending of light
rays when they pass through a
substance.
Convex and Concave Mirrors
Images in convex mirrors
are always smaller.
Images in concave mirrors
are always bigger.
Convex and Concave Lenses
• Convex Lenses are
used as a Magnifier
• Concave Lenses are
used as a De-magnifier
Convex Lenses
• People who are farsighted
have trouble seeing things
that are close to them
(reading) Glasses or
contacts with convex lenses
magnify the print
• Movie projectors use convex
lenses. As light from the
bulb shines through the film,
light rays spread apart. As
these rays pass through the
projector lens, they bend
toward each other again.
Concave Lenses
• Concave lenses help people
who are nearsighted. These
people have trouble seeing
distant objects. Concave
lenses bend light rays
outward just enough to
make distant objects seem
closer.
• Some cameras have a
concave lens in their
viewfinder, you see a small
version of what the final
photograph wil look like.
Key Vocabulary
 lens – a piece of clear material that bends,
or refracts, light rays passing through it.
 Convex lens – is thicker in the middle than
at the edges.
 Concave lens – is thicker at the edges
than in the middle.
Using Light, Lenses, and
Mirrors for space
exploration
Refracting Telescope
In Galileo's version, light
entering the far end (1)
passed through a convex
lens (2), which bent the
light rays until they came
into focus at the focal
point (f). The eyepiece (3)
then spread out (magnified)
the light so that it covered
a large portion the viewer's
retina and thus made the
image appear larger.
Reflecting Telescope
In Newton's version, light
streaming in one end (1)
reflected off a concave
mirror fixed inside the
other end (2), then off a
flat mirror set an angle (3).
The light came into focus
at the focal point (f) and
then was magnified for the
viewer by the eyepiece (4).
Take a ride on
the Magic School Bus!