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Light
In this unit:
1)
2)
3)
4)
Properties of light
Reflection
Colours
Refraction
Part 1 – Properties of Light
Light travels in straight lines:
Laser
Light travels VERY FAST – around
300,000 kilometres per second or
186,000 km/sec.
At this speed it can
go around the world 8
times in one second.
Light travels much faster than sound. For example:
1) Thunder and lightning
start at the same time,
but we will see the
lightning first.
2) When a starting pistol
is fired we see the
smoke first and then
hear the bang.
We see things because they
reflect light into our eyes:
Homework
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
What happens when light strikes
glass? Or waxed paper? Or a book?
If light travels through
an object it is
=transparent
If light is blocked by an
object and a dark
shadow is cast it is=
opaque.
If some light passes
through but not all and
a light shadow is
present it
is=translucent.
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.
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.
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.
Part 2 - 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 !!!
Using mirrors
Two examples:
2) A car headlight
1) A periscope
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 pen is
placed in water it looks like this:
QuickTime™ and a
decompressor
are needed to see this picture.
In this case the light rays are slowed down by the water
and are _____, causing the pen to look odd. The two
mediums in this example are ______ and _______.
Words – speed up, water, air, bent, medium
What is light really?
Electromagnetic radiation waves
Notice the wavelength is long(Radio waves) and gets shorter (Gamma Rays)
*Electromagnetic Radiation
The only difference amongst radio
waves, visible light, and gamma-rays
is the amount of energy of the
photons. Radio waves have photons
with low energies. Microwaves have a
little more energy than radio waves.
Gamma-rays and cosmic rays have
highest energy waves and are the
deadliest.
*Page info from NSTA Conference 2004
Diagram and label a representation of a
light wave (wavelength, peak, trough)
Radio
(Longest electromagnetic waves)
Emitted by
– Astronomical Objects
– Radio Station
Transmitters
Detected by
– Ground based radio
telescopes
– *If you turn on a radio,,
it will convert the radio
wave energy into sound
energy.
Television
Shorter than radio, also
used to carry messages
(pictures & sound) to our
TV sets.
*We can sense the TV
waves around us with our
televisions.
Microwave
Emitted by:
– Gas clouds collapsing
into stars
– Microwave Ovens
– Radar Stations
– Cell Phones
Detected by
– Microwave Telescopes
– Food (heated)
– Cell phones
– Radar (systems)
Infrared
(Heat or Thermal)
Are you a source of infrared? YES you are!
Emitted by
– Sun and stars (Near)
– TV Remote Controls
– Food Warming
Lights (Thermal)
– *Everything at room
temperature or
above,=HEAT
Detected by
– Infrared Cameras
– TVs, VCRs,
– Your skin
Visible
Each color is a different size wave.
Red the longest & violet the shortest
QuickTime™ and a
decompressor
are needed to see this picture.
Ultraviolet
Sunburn / black light
Emitted by
– Tanning booths (A)
– The sun (A)
– Black light bulbs (B)
– UV lamps
Detected by
– Space based UV
detectors
– UV Cameras
– Flying insects (flies)
X-ray
Emitted by
– Astronomical
objects
– X-ray machines
– CAT scan machines
– Older televisions
– Radioactive minerals
– Airport luggage
scanners
Detected by
– Space based X-ray
detectors
– X-ray film
– CCD detectors
Gamma Ray
(Short electromagnetic waves but more
energetic)
Emitted by
– Radioactive materials
– Exploding nuclear
weapons
– Gamma-ray bursts
– Solar flares
Detected by
--Geiger counters
– Gamma detectors and
astronomical satellites
– Medical imaging
detectors
Sources of g-ray Emission
• Black holes
• Active Galaxies
• Pulsars
• Diffuse emission
• Supernovae
• Gamma-ray bursts
• Unidentified
COSMIC Rays
(The highest energy waves and the
deadliest)
Cosmic rays come from
deep space and can pass
through the Earth.
A great question!
Radio waves= (Buildings to
human size);
Microwaves
(Humans-beetles);
Infrared waves
(Eye of a needle);
Visible waves
(microscopic size)!
WOW! All the rest are the size of
molecules, atoms, atomic nuclei
and smaller..
Remember
Remember
radioradio
waves
waves
are long…and
are long…and
gamma
gamma
rays rays
are small
are small
Radio-TV -Microwave- Infrared - VISIBLE -Ultraviolet -X-rays - Gamma- Cosmic
Radio-TV -Microwave- Infrared - VISIBLE -Ultraviolet -X-rays - Gamma- Cosmic
Convex Lens
A Convex lens
causes light to
converge, or
focus, producing
an image that is
smaller than the
original object.
Concave Lens
A Concave lens
causes light to
diverge, or spread
out, producing a
larger image than
the original
object.
Optical Tools
Identify some
common optical
tools, and describe
whether each has
lenses, mirrors,
and/or prisms in it.
These should
include:
– eyeglasses
– flashlights
– cameras
– binoculars
– microscopes
Essential Knowledge, Skills,
and Processes
Describe the contributions of these
scientists in creating and using optical
tools:
– Galileo Galilei
– Robert Hooke
– Anton van Leeuwenhoek
– Isaac Newton
Galileo Galilei
Italian
Lived from 1564-1642
Developed the refracting telescope
Developed the first known example of the
microscope
Robert Hooke
English
Lived from 1635-1703
Devised the compound
microscope and
illumination system
Discovered plant cells
Examined fossils with a
microscope
Anton van Leeuwenhoek
Dutch; born in Holland
Lived 1632-1723
Made over 500 simple microscopes
Discovered bacteria, free-living and parasitic
microscopic protists
Isaac Newton
English
Lived from 1643-1727
Discovered that white light was not a simple
entity, but splits into a range of colors
When he passed white light through a glass
prism, he noted that a spectrum of light
was formed; particle theory of light
Reflecting telescope
Colour
White light is not a single colour; it is made
up of a mixture of the seven colours 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.
The colours of the rainbow:
Red
Orange
Yellow
Green
Blue
Indigo
Violet
Adding colours
White light can be split up to make separate colours.
These colours can be added together again.
The primary colours of light are red, blue and green:
Adding blue and red
makes magenta
(purple)
Adding red
and green
makes yellow
Adding blue and
green makes cyan
(light blue)
Adding all
three makes
white again
Seeing colour
The colour an object appears depends on the colours
of light it reflects.
For example, a red book only reflects red light:
White
light
Only red light
is reflected
A pair of purple trousers 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 colours:
White
light
Using coloured light
If we look at a coloured object in coloured
light we see something different. For
example, consider a football kit:
Shirt looks red
White
light
Shorts look blue
In different colours of light this kit would look different:
Red
light
Shirt looks red
Shorts look black
Shirt looks black
Blue
light
Shorts look blue
Using filters
Filters can be used to “block” out different colours of light:
Red
Filter
Magenta
Filter
Sound – The basics
We hear things when they vibrate.
If something vibrates with a high frequency (vibrates very
______) we say it has a _____ pitch.
If something vibrates with a low frequency (vibrates
______) we say it has a ____ pitch.
The lowest frequency I could hear was…
Words – slowly, low, high, quickly
Drawing sounds…
This sound wave has a
_____ frequency:
This sound wave has a
___ _frequency:
Drawing sounds…
This sound wave has a
_____ amplitude
(loud):
This sound wave has a
_____ amplitude
(quiet):
Hearing problems
Our hearing range can be damaged by several
things:
1) Too much ear wax!
2) Damage to the auditory nerve
3) Illness or infections
4) Old age (not like Mr Richards)
Other sound effects…
Like light, sound can be…
1) Reflected – sound reflections are called
______.
2) Refracted – this is why you might sound
strange if you try talking underwater
The Ear
Label your diagram with the following:
These bones are vibrated by the eardrum
This tube carries the sound towards the eardrum
This part is used to help us keep our balance
This part “picks up” the vibrations
This part of the ear contains many small hairs with turn
vibrations into an electrical signal
This part connects the ear to the mouth
This part “channels” the sound towards the ear drum
Investigating filters
Colour of filter
Red
Green
Blue
Cyan
Magenta
Yellow
Colours that could be “seen”
Some further examples:
Object
Red socks
Blue teddy
Colour of light
Colour object
seems to be
Red
Red
Blue
Black
Green
Black
Red
Black
Blue
Green
Red
Green camel
Blue
Green
Red
Magenta book
Blue
Green
Red
Blue
Green
Yellow
Cyan
Magenta
White
The Ear