Transcript Physical Science - Central Davidson High School

Physical Science
Ch. 12 & 13:
Electromagnetic Waves and
Light
Electromagnetic Radiation
• Electromagnetic waves (E.M.) are
transverse waves produced by the motion
of electrically charged particles (photons).
• E.M. waves do not require a medium, and
are therefore able to travel at 186,000 mi/s
(300,000 km/s), the speed of light (which is
an E.M. wave).
Does Light Have Mass?
• Well…….maybe.
Electromagnetic Spectrum
• The different electromagnetic waves are
arranged in the electromagnetic
spectrum in order of increasing
frequency and decreasing wavelength.
• The higher the frequency, the more
photons (energy) per wave, and the
more potentially harmful the wave is.
Low energy
High energy
Radio Waves
• Radio waves are the lowest
frequency E.M. wave.
• They are used primarily for
communications, such as cell
phones, t.v. and radio
transmissions, and cordless
devices such as phones,
speakers, etc.
Microwaves
• Microwaves are a type of radio wave. They are
used in cell phones and microwave ovens.
• At normal levels, microwaves are harmless.
• Why shouldn’t you put metal objects (or CD’s) in
a microwave?
•
•
•
•
Metal foil
CD
Bulb
Chips
Infrared Radiation
• Infrared radiation transfers energy in the
form of heat.
• Examples include heat lamps and the
warmth from the sun. Special types of film
and cameras can show infrared radiation.
This is called thermography.
Visible Light
• Visible light can be separated into 7 different
colors. From lowest frequency to highest, they
follow the acronym ROY G. BIV
• When all 7 colors are combined together they
produce white light.
• When all 7 colors of the spectrum are
absent, then the “color” black is produced.
• What is a “black” light and how does it
work?
Colors
• When an object appears a
certain color, it is because that
is the color which is being
reflected back to your eye, just
like a mirror.
• A white object reflects all
colors, a black object reflects
no color.
Visible Light Spectrum
• A prism can separate visible light into the 7
different colors.
• Drops of moisture in the atmosphere can
act as a prism, and form a rainbow.
• A pigment is a colored material which is
used to change the color of other
materials.
• The 3 primary pigments are magenta, cyan, and
yellow (pg. 393). These colors can be combined to
produce any other color of pigment.
• So if you go to the store and pick
out a certain color of paint, odds
are they will not have that color
on the shelf. But they will mix
the correct proportions of the
primary pigments together to
create your color.
• Visible light can also
cause certain
chemical reactions to
occur.
• Examples:
photosynthesis, milk
spoiling, H2O2
breakdown
Is it possible to see in the dark?
Ultraviolet Light (U.V.)
• U.V. rays are potentially dangerous at high
levels or with prolonged exposure.
• U.V. rays can cause sunburns and skin
cancer, and kill bacteria and healthy cells.
• The ozone layer of the
atmosphere blocks most u.v.
rays from reaching the earth.
• Using sunscreens with high
S.P.F. ratings can also help
protect your skin from u.v.
rays.
X-Rays
• X-rays are high frequency
e.m. waves which are
potentially dangerous at
moderate levels.
• X-rays can penetrate many
materials such as skin,
muscle, and many fabrics.
• X-rays are used in dental
and medical procedures,
and can cause cancer and
decrease a persons life
expectancy with prolonged
exposure.
Gamma Radiation
• Gamma radiation is high frequency waves which
can be extremely dangerous.
• Potentially dangerous gamma rays may be
given off from radioactive materials, and are
present everywhere on earth at low safe levels.
• Gamma radiation can kill healthy cells,
but can also be used to kill cancerous
cells. This is called radiation therapy.
Classifications of Materials
• Different materials can be classified by how
they allow waves (usually light) to pass
through them.
• These classifications are opaque,
translucent, and transparent.
• Transparent materials allow
almost all visible light to pass
through.
Ex.: glass, plastic wrap
• Translucent materials allow a partial
amount of visible light to pass through.
Ex.: wax paper, shower doors, plastic milk
jugs
• Opaque materials stop almost all
visible light from passing through.
Ex.: drywall, thick curtains
Types of Lighting
• There are 2 main types of
artificial lighting.
1. Incandescent – a heated filament
excites the gases inside an
enclosed bulb.
2. Fluorescent – an electric current is
transferred through a glass tube filled with
a conductive gas. A small amount of
mercury inside emits u.v. rays when
energized. These rays excite phosphors
on the inside of the tube, producing light.
Polarized Light

Normal light will produce waves which
vibrate in many different planes.

Polarized light is light which vibrates in only
1 plane. This is created by passing normal
light through a polarized lens.
• Polarized lenses block all light waves except
those moving in 1 particular plane.
• Think of polarized lenses like tines on a
comb. Normal light that passes through the
lens, like tangled hair through a comb, will
align in the same plane.
• Polarized glass and lenses are effective at
blocking out glare from the sun.
As a result they are used in car windshields,
sunglasses, and camera lenses.
Lasers & Coherent Light
• Coherent light is visible light traveling at only 1
specific wavelength (resulting in 1 color). This
wave has all of it’s crests and troughs aligned and
travels in only 1 direction. A laser is an example
of coherent light.
• A laser is a device used to create a
beam of coherent light.
Lasers

In a laser, an electric current excites a
material (like neon) and causes it to emit
photons. These photons are enclosed
inside the laser device where they
bounce back and forth between 2
mirrors and becomes perfectly aligned
(coherent light).

Some of these photons, if they are aligned
correctly, escape through a small portion of
one of the mirrors. This is the laser beam.
• Think of it like a piggy bank. If you want
to get some money out through the top
slit, the coins have to line up perfectly
before they will come out.
• Since laser beams are perfectly aligned and
move in the same exact direction, they spread
out very little.
Total Internal Reflections
• Normally, when a wave enters a medium it is
either reflected or re-emitted out of the medium.
However, when a wave entering a medium is
completely reflected back into the material
instead of out of it, this is called a total internal
reflection.
• Optical fibers (Fiber optics) produce
a total internal reflection. Such
fibers can be used for
communications, entertainment, and
surgeries.
Certain “fluorescent” plastics
produce internal reflections which
may make them appear to glow.
• A mirage is a visual distortion produced by
the refraction of light.
• Some mirages produce a mirror or a watery
image, and others may make an object
appear larger or smaller, nearer or further
away.
• This device produces a false image, but
not a true mirage.
• Paul bought a very bright LED flashlight. He
showed Dave how bright it was by shining a
regular light in his eyes, and then the LED. After
viewing the LED for a few seconds, the room
suddenly appeared darker to Dave. Why?
• Not to be outdone, Dave then pulls out a
laser pointer which he had and said, “Well
just look at how bright this one is.”
Bad idea. Why?
• I cdnuolt blveiee taht I cluod aulaclty
uesdnatnrd waht I was rdanieg. The
phaonmneal pweor of the hmuan mnid.
Aoccdrnig to rscheearch at Cmabrigde
Uinervtisy, it deosn't mttaer in waht oredr
the ltteers in a wrod are, the olny iprmoatnt
tihng is taht the frist and lsat ltteer be in
the rghit pclae. The rset can be a taotl
mses and you can sitll raed it wouthit a
porbelm. Tihs is bcuseae the huamn mnid
deos not raed ervey lteter by istlef, but the
wrod as a wlohe. Amzanig huh?
• How do you suppose they were able to
etch the image into the middle of the glass
cube?
• Todd was showing a
friend how his black
light worked, when
his white cat walked
in the room. What
color did the cat
appear under the
black light, and why?
• Les spilled a little bit of oil into the water as
he was working on his boat. This caused a
rainbow effect to appear. Why do you think
this occurred?
• Karen went to the beach last week, and
because it was a cloudy day she did not use any
sunscreen. To her dismay, she came back with
a slight sunburn. How is this possible?
• How is one universal remote able to
control all of the components in your
entertainment system (tv, DVD, cable box,
etc.) by itself)
»
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• In art class, Andy was mixing watercolors
together to obtain the right shades for his
project. He found that using the 3 primary
pigment colors, there were only 2 main “colors”
which he could not produce. What were they?
• When asked what he was doing outside on
the ground, Beaman replied, “Creating
constructive interference by simultaneous
refraction of mid-level electromagnetic
radiation through a convex lens, in order to
harness their combined energies and
thermally terminate formicidae hymenoptera
with extreme prejudice.”
What was he doing?